Organocatalytic, regioselective allylic- and 1,6-substitution of quinone monoketals with diaryl H-phosphine oxides

Journal of Organometallic Chemistry 885 (2019) 21e31

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Organocatalytic, regioselective allylic- and 1,6-substitution of quinone monoketals with diaryl H-phosphine oxides Biquan Xiong*, Gang Wang, Congshan Zhou, Yu Liu, Chang-An Yang, Panliang Zhang, Kewen Tang, Quan Zhou** Department of Chemistry and Chemical Engineering, Hunan Institute of Science and Technology, Yueyang, 414006, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 20 November 2018 Received in revised form 26 December 2018 Accepted 31 December 2018 Available online 7 February 2019

An efficient selective synthesis of C- and O-phosphoryl-substituted phenols from easily available diaryl H-phosphine oxides with quinone monoketals (QMAs) has been developed. With the assistance of opponent characteristic additives (e.g., H2O and Et3N), diaryl H-phosphine oxides could selectively proceed the allylic- and 1,6-substitution to conjugate with the C-/O- positions of QMAs. The reported protocol is green and practical, and represents an efficient method to functionalize C-/O-phosphorylsubstituted phenols with moderate to good yields. © 2019 Elsevier B.V. All rights reserved.

Keywords: Organocatalysis Quinone monoketals (QAMs) Allylic-substitution 1,6-substitution Diaryl H-phosphine oxides

1. Introduction Due to the importance of organophosphorus compounds in agrochemicals, pharmaceuticals and functional materials, designing effective and straightforward methods for the construction of P-C/P-Z (Z ¼ O, S, N, etc.) bonds has been the leading tasks in synthetic organic chemistry [1]. Especially some of the phosphine oxides or phosphinates, which contain special functional groups, are used as versatile chiral synthetic intermediates. Usually, the expected organophosphorus compounds could be obtained through the classical methods such as Michaelis-Arbuzov reaction and Atherton-Todd reaction [4c], but these methods always need nucleophilic reagents or phosphoryl chlorides [2], as well as the airsensitive and/or toxic reagents with the low tolerance of functional groups and strict substrate limitations [3,4]. The traditional methods for the preparation of phosphorylsubstituted phenols significantly depend on the rearrangement of ortho-lithiated phosphoryl-derivatives of phonols [5]. According to the previous studies, Melvin has investigated the migration of

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (B. Xiong), [email protected] (Q. Zhou). https://doi.org/10.1016/j.jorganchem.2018.12.020 0022-328X/© 2019 Elsevier B.V. All rights reserved.

phosphorus in the ortho-lithiated derivatives of (RO)2P(O)-O-aryl and (RO)(OAr)P(O)-O-aryl/alkyl phosphates in details in 1981 [5a]. Balram and co-workers explored the metalation-induced 1,3migration of a diphenylphosphinyl group from oxygen to carbon for the preparation of corresponding 2-(diphenylphosphinyl)phenols in 1988 [5b]. In 2004, the migration of phosphorus from oxygen to the aromatic carbon atom in the ortho-lithiated derivatives was reported by Gorobets and Wu [5c-d]. In addition, the reduction and reductive alkylation of ortho-lithiated diethyl arylphosphonates in the presence of an alkyl halide was disclosed by Heinicke and co-workers in 2007 [5e]. In 2014, Yin and Han have investigated the Cu-catalyzed stereospecific cross-coupling of P(O)-H compounds with 2-halides, where the (Rp)-/(Sp)-phosphorylsubstituted phenols could be selectively synthesized via the different procedures [6g]. Kita and co-workers have demonstrated that QMAs are wellappreciated intermediate for allylic/1,6-substitution reactions on account of their intrinsic electrophilic property [7b-c,7g]. To avoid the modification of reactants or the intermediates, the direct substitution of QMAs with organophosphorus compounds containing a P(O)-H moiety under environment-benign conditions becomes an efficient and promising strategy for the formation of phosphorylsubstituted phenols [6,7]. As an ongoing effort on the construction of P-C/P-O bonds, we herein report an efficient and simple allylic- and 1,6-substitution of diaryl H-phosphine oxides with

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QMAs under mild conditions using the cheap small molecule catalysts (e.g., H2O and Et3N). Compared with the traditional methods, the present method is green and efficient, and avoids the use of transition-metals and air-sensitive reagents [6,8,9]. 2. Results and discussion As a first examination, we investigated the reaction of 4,4dimethoxycyclohexa-2,5-dienone (1a) with Ph2P(O)H (2a) in CH2Cl2 at 40  C under N2 atmosphere; the corresponding product of (2-hydroxy-5-methoxy-phenyl)diphenylphosphine oxide (3a) was generated in 15% yield. The increase of the temperature within 40e100  C range is beneficial for the reaction, but a further increase from 100 to 120  C can not promote the yield significantly (Table 1 entries 1e5). We next examined the effects of different solvents (e.g., CH3CN, DCE, THF, toluene, 1,4-dioxane, DMF, EtOAc) on the reactions. To our delight, the 66% yield of 3a was obtained and significantly more excellent than the others when toluene was used as the solvent (Table 1, entries 6e12). Encouraged by the previous reports [6,10], we further considered the influences of the additives, among the Brønsted acids (e.g., benzoic acid, salicylic acid, acetic acid, diphenyl phosphinic acid and H2O). Accordingly, H2O gave the best result (Table 1, entries 13e17). And then the effect of H2O loading was studied. It can be found that the product yield decreases from 92% to 86% with the amount of H2O reduced from 10 to 5 mol %. The increase of H2O from 10 to 20 mol % causes the increase of the product yield from 92% to 99%, while the yield could not be promoted meaningfully with a further promotion of the H2O Table 1 Optimization of the allylic-substitution reaction conditions.a

Entry

Catalyst

Solvent

Temp.(oC)

Yieldb

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

e e e e e e e e e e e e PhC(O)OH Salicylic acid CH3C(O)OH Ph2P(O)OH H2O H2O

CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH3CN DCE THF Toluene 1,4-Dioxane DMF EtOAc Toluene Toluene Toluene Toluene Toluene Toluene

40 60 80 100 120 100 100 100 100 100 100 100 100 100 100 100 100 100

15% 22% 48% 53% 54% 35% 42% 35% 66% trace 22% 30% 82% 79% 85% 84% 92% 86%c

19 20

H2O H2O

Toluene Toluene

100 100

99%d 97%e

a Reagents and conditions: 4,4-dimethoxycyclohexa-2,5-dienone (0.6 mmol), Ph2P(O)H (0.5 mmol), and catalyst (10 mol%) in solvent (1.0 mL), under N2 atmosphere stirred at 100  C for 12 h. b Yield determined by GC analysis, using dodecane as the internal standard. c H2O (5 mol%). d H2O (20 mol%). e H2O (50 mol%).

loading to 50 mol% (Table 1, entries 18e20). As shown in Table 2, the H2O-catalyzed allylic substitution reaction can be applied to a variety of QMAs. Under the optimized reaction conditions, 4,4-dimethoxycyclohexa-2,5-dienone (1a) could react efficiently with Ph2P(O)H (2a) to afford the corresponding allylic-substitution product of 3a in 97% isolated yield. The use of unsymmetric QMAs was subsequently investigated. When 4-ethoxy-4-methoxycyclohexa-2,5-dienone (1b), 4methoxy-4-propoxycyclohexa-2,5-dienone (1c) and 4isopropoxy-4-methoxycyclohexa-2,5-dienone (1d) are applied, the reactions of them with diphenyl phosphine oxide (2a) could afford the corresponding products of 3b (with 3a at a ratio of 68/32), 3c (with 3a at a ratio of 83/17) and 3d (with 3a at a ratio of 92/8) in 61e83% yields, respectively. In addition, it is observed that o-QMAs of 4-allyl-6,6-dimethoxycyclohexa-2,4-dienone (1e), 4-allyl-6-ethoxy-6-methoxy-cyclohexa-2,4-dienone (1f) and 4allyl-6-isopropoxy-6-methoxycyclohexa-2,4-dienone (1g) also exhibit high reactivity toward the reactions, affording the corresponding products of 3e-3g (3f with 3e at a ratio of 79/21, 3g with 3e at a ratio of 91/9) in 72%e88% yield. Additionally, strong electron-withdrawing groups (e.g., -Cl) substituted QMAs were further investigated, such as 2-chloro-4,4-dimethoxycyclohexa2,5-dienone (1h), 2-chloro-4-ethoxy-4-methoxy-cyclohexa-2,5dienone (1i), 2-chloro-4-methoxy-4-propoxycyclohexa-2,5dienone (1j), and 2-chloro-4-isopropoxy-4-methoxycyclohexa2,5-dienone (1k). The corresponding products were only formed in 55e69% yields at 120  C (3i with 3h at a ratio of 69/31, 3j with 3h at a ratio of 76/24, 3k with 3h at a ratio of 92/8). This phenomenon may be ascribed to the deactivating effects of the electronwithdrawing group on the dienone ring of these substrates. The tendency for the leaving group of unsymmetric QMAs mainly depends on the steric hindrance. In addition, we have further checked the reaction of 4,4-diethoxycyclohexa-2,5-dienone (1l) with diphenyl phosphine oxide (2a), and the corresponding allylic substitution product of 3b was gained in 88% yield (Fig. 1). As depicted in Table 3, we have further investigated the reaction of different types of H-phosphine oxides (2b-2m) with 4,4dimethoxycyclohexa-2,5-dienone (1a) under the optimized conditions. It is worth noting that di-p-tolylphosphine oxide (2b), dim-tolylphosphine oxide (2c), bis(3,5-dimethylphenyl) phosphine oxide (2d), and bis(4-methoxyphenyl) phosphine oxide (2e) react efficiently with 4,4-dimethoxycyclohexa-2,5-dienone (1a) to give the corresponding allylic substitution products of 4a-d in 78e93% yields. In addition, (2-hydroxy-5-methoxyphenyl) bis(4-(trifluoromethyl)phenyl) phosphine oxide (4e) was also formed in 69% yield under the present reaction conditions. When di(naphthalen2-yl)phosphine oxide (2g) and di(naphthalen-1-yl)phosphine oxide (2h) were used, (2-hydroxy-5-methoxyphenyl)di(naphthalen2-yl) phosphine oxide (4f) and (2-hydroxy-5-methoxyphenyl) di(naphthalen-1-yl) phosphine oxide (4g) were obtained in 72% and 64% yield, respectively. 9,10-Dihydro-9-oxa-10phosphaphenanthrene 10-oxide (2i) was also tested for the reaction, but the expected product of 6-(2-hydroxy-5-methoxyphenyl)6H-dibenzo[c,e][1,2]oxaphosphinine -6-oxide (4h) was only formed in 26% yield. We have further used diphenyl phosphonate (2j), n-butyl phenyl phosphine oxide (2k), di-n-butyl phosphine oxide (2l), and dicyclohexyl phosphine oxide (2m) as the phosphorylation reagents in the allylic substitution reaction with 1a under the optimized reaction conditions. To our surprise, the corresponding substitution products were not detected after the reaction. This phenomenon may be ascribed to the low reactivity of these types of compounds for the present reaction conditions. Surprisingly, while we performed the reaction of 4dimethoxycyclohexa-2,5-dienone (1a) with 9,10-dihydro-9-oxa10-phosphaphenanthrene 10-oxide (2i) (DOPO) in the presence of

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Table 2 Allylic substitution: scope of the QMAs.a

a Reagents and conditions: QMAs (0.6 mmol), Ph2P(O)H (0.5 mmol), and H2O (20 mol%) in toluene (1.0 mL), under N2 atmosphere stirred at 100 oC for 12 h. The products from the reactions of diaryl phosphine oxides with unsymmetric QMAs could be easily separated by passing the crude product through a short silica gel column (Hexane/EtOAc (2:1-5:1)). b Isolated yield. c GC yield. d 120 oC.

Fig. 1. ORTEP drawing of compound 3a. Hydrogen atoms are omitted for clarity, ellipsoids are drawn at 50% probability. Selected bond lengths [Å] and angles [deg]: P1O3 1.488(2), P1-C1 1.795(3), P1-C8 1.801(3), P1-C14 1.795(3), O1-C2 1.354(3), O2-C5 1.370(3), O2-C7 1.415(5), O3-P1-C1 110.4(1), O3-P1-C8 109.8(1), C1-P1-C14 110.1(1), C8-P1-C14 106.7(1), P1-C14-C15 124.2(2), P1-C14-C19 117.3(2) [11].

an organic base (e.g. Et3N) instead of H2O at room temperature, the corresponding 1,6-substitution product of 5a was synthesized in 18% yield (Table 4, entry 1). With the increase of the use of Et3N from 10 mol% to 20 mol%, the yield of the expected 1,6-substitution product was increased to 34% accordingly. While we further increased the amount of Et3N from 20 mol% to 100 mol%, the yields did not change notably. Therefore, we chose 20 mol% of Et3N as the optimal amount of the catalyst (Table 4, entries 2e4). Increasing the reaction temperature from 25  C to 80  C could bring a sharp increase of the yield from 34% to 92%, and further increase of the temperature to 100  C could not alter the yield meaningfully (Table 4, entries 5e8). With the optimal reaction conditions in hand, we then next explored the selective 1,6-substitution of 9,10dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (2i) with the derivatives of QMAs. As described in Table 5, QMAs derivatives such as 4,4dimethoxycyclohexa-2,5-dienone (1a), 4-ethoxy-4-methoxycyclohexa-2,5-dienone (1b), 4-methoxy-4-propoxycyclohexa-2,5dienone (1c), 4-isopropoxy-4-methoxycyclohexa-2,5-dienone (1d) were employed. The desired products of 5a-5d were given in 76e90% yields (5b with 5a at a ratio of 81/19, 5c with 5a at a ratio of 87/13, 5d with 5a at a ratio of 91/9). Furthermore, other QMAs which were substituted with an electron-withdrawing group on the cyclohexa-2,5-dienone ring (e.g., 2-chloro-4,4dimethoxycyclohexa-2,5-dienone (1h), 2-chloro-4-ethoxy-4methoxycyclohexa-2,5-dienone (1i), 2-chloro-4-methoxy-4propoxycyclohexa-2,5-dienone (1j), 2-chloro-4-isopropoxy-4methoxycyclohexa-2,5-dienone (1k)) could also be tolerated with the reaction, and the corresponding products were obtained in

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Table 3 Allylic substitution: scope of the H-phosphine oxides.a

a Reagents and conditions: 4,4-dimethoxycyclohexa-2,5-dienone (0.6 mmol), H-phosphine oxides (0.5 mmol), and H2O (20 mol%) in toluene (1.0 mL), under N2 atmosphere stirred at 100 oC for 12 h. b Isolated yield.

Table 4 Optimization of the 1,6-substitution reaction conditions.a

Entry

Catalyst (mol%)

Temp. (oC)

Yield of 5ab

1 2 3 4 5 6 7 8

Et3N Et3N Et3N Et3N Et3N Et3N Et3N Et3N

25 25 25 25 40 60 80 100

18% 34% 36% 38% 85% 90% 92% 89%

(10 mol%) (20 mol%) (50 mol%) (100 mol%) (20 mol%) (20 mol%) (20 mol%) (20 mol%)

Yield determined by GC analysis, using dodecane as the internal standard. a Reagents and conditions: QMAs (0.6 mmol), 9,10-dihydro-9-oxa-10phosphaphenanthrene 10-oxide (0.5 mmol), and Et3N (20 mol%) in toluene (1.0 mL), under N2 atmosphere stirred at 80  C for 12 h. b Isolated yield.

69e79% yields with the selectivity of 5f with 5e at a ratio of 77/23, 5g with 5e at a ratio of 86/14, 5h with 5e at a ratio of 92/8. In order to demonstrate the practical application of this method, a large-scale reaction for the allylic substitution of diphenyl phosphine oxide (2a, 10 mmol) with 4,4-dimethoxycyclohexa-2,5dienone (1a, 12 mmol) was performed and generated 3a in 92% yield (Scheme 2). The competition reactions of diphenyl phosphine oxide (2a) with 4,4-dimethoxycyclohexa-2,5-dienone (1a) and 2-chloro-4,4dimethoxycyclohexa-2,5-dienone (1h) were carried out at the indicated temperatures, where 2a was used as the internal standard. When the reactions were treated at 100  C, the allylic substitution yields (31P NMR yield) of 3a and 3h were 78.6% and 16.2%, respectively. When we further increased the temperature from 100  C to 120  C, the yield of 3h was not increased significantly (3a: 71.5%, 3h: 24.7%). This phenomenon may be ascribed to the strong electron-withdrawing effect of the halogen atom (-Cl) on the dienone ring, leading to the low reactivity of this type of compounds (Scheme 3). When the H-phosphites (diethyl H-phosphite) and H-phosphinates (ethyl phenyl H-phosphinate) were employed for the allylic-/ 1,6-substitution reactions, the expected products of 7a-d could not be observed after the reaction. In addition, we have further used diphenyl phosphine oxide and di(naphthalen-2-yl) phosphine oxide as the substrates for the 1,6-substitution reactions, as monitored by GC-MS and 31P NMR, the corresponding 1,6-substitution

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25

Table 5 Scope for the 1,6-substitution.a

a

Reagents and conditions: QMAs (0.6 mmol), 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (0.5 mmol), and Et3N (20 mol%) in toluene (1.0 mL), under N2 atmosphere stirred at 80 oC for 12 h. The products from the reactions of DOPO with unsymmetric QMAs could be easily separated by passing the crude product through a short silica gel column (Hexane/EtOAc (2:1-5:1)). b Isolated Yield. c Yield determined by GC analysis, using dodecane as the internal standard.

Scheme 2. Large-scale production of 3a.

Scheme 3. Competition reaction.

Scheme 1. Strategies for the preparation of phosphoryl-substituted phenols.

products of 7e-f were not detected after the reaction (Scheme 4). As clearly depicted in Scheme 5, a plausible mechanism was proposed for the selective allylic substitution reaction of diaryl Hphosphine oxides with QMAs [6g,10]. Firstly, quinone monoketal (A) is attacked by Hþ to give the cation B with the release of

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Scheme 6. Plausible mechanism for the 1,6-substitution reaction. Scheme 4. Control experiments.

reaction, and Et3N is regenerated to the catalytic cycle. In summary, we have developed an efficient method for the selective allylic and 1,6-substitution of QMAs with diaryl H-phosphine oxides, yielding the corresponding C- and O-phosphorylsubstituted phenols with moderate to good yields. The approach avoids the use of transition metals and toxic reagents, and the reaction can be performed under mild conditions, making the experimental procedure simple. The synthetic method has high potential for the synthesis of functional group organophosphorus compounds, biologically active molecules, and catalytic ligands. 3. Experimental 3.1. General considerations

Scheme 5. Plausible mechanism for the allylic substitution reaction.

methanol. On the other hand, diaryl H-phosphine oxide (C) undergoes the tautomerization to generate the intermediate D. The intermediate D coordinates with B via the hydrogen bond to afford E, and then E undergoes the allylic substitution to afford the intermediate F. In the presence of OH, the hydrogen atom would be snatched from F to yield H2O. Thus, H2O acts as the catalytically active species in the catalytic cycle. Finally, with the aromatization, the allylic substitution product of G is formed. In contrast, the mechanism for 1,6-substitution is quite different with allylic substitution (Scheme 6). Firstly, a catalytic amount base

(Et3N, H) attacks the double bond of the quinone monoketal (A) to yield the corresponding adduct I. Then H would undergo the intermolecular tautomerization to afford the intermediate J. With the release of one molecule of R-OH, K is generated in-situ via the aromatization of J. In the presence of DOPO, K would be protonated by DOPO to afford the ionic adduct M. Finally, the 1,6-substitution product N is subsequently formed via the 1,6-substitution

All solvents used in the reactions were freshly distilled. The other reagents were recrystallized or distilled as necessary. All reactions were performed under an atmosphere of dry nitrogen unless specified otherwise. 1H (400 MHz), 13C (100 MHz), and 31P (162 MHz) spectra were recorded on a 400 MHz spectrometer in CDCl3. 1H NMR chemical shifts were reported using TMS as internal standard while 13C NMR chemical shifts were reported relative to CDCl3. The electron ionization method was used for HRMS measurements, and the mass analyzer type was double-focusing. 3.2. General procedure for preparation of quinone monoketals (QMAs) [12]

To a stirred solution of appropriate-methoxyphenol (1.0 equiv) in dry MeOH (200 mL) at 0  C under nitrogen atmosphere was added phenyliodonium diacetate (PIDA; 1 equiv) portionwise and the resulting mixture was stirred at 0  C for 45 min. The reaction was quenched with saturated NaHCO3 aqueous solution (300 mL) and was extracted with Et2O (3  400 mL). The combined organic layer was washed with brine, dried over MgSO4, and was

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concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (basified with 0.1% Et3N) using hexane/EtOAc (4:1 to 1:1) as eluent to afford the quinone as colorless oil. Compounds of 1b-1k were synthesized by the general procedure. 3.3. General procedure for the allylic-/1,6-substitution reaction A mixture of quinone monoketal (0.6 mmol), H-phosphine oxide (0.5 mmol), and catalyst (20 mol% of H2O for allylic substitution, 20 mol% of Et3N for 1,6-substitution) was dissolved in toluene under N2 atmosphere, stirred at 100  C or 80  C for 12 h. Upon completion of the reaction, the mixture was concentrated under vacuum. Removal of the solvent under a reduced pressure gave the crude product; pure product was obtained by passing the crude product through a short silica gel column using Hexane/EtOAc (2:1e5:1) as eluent. 3.3.1. Analytical data for compounds 3.3.1.1. (2-Hydroxy-5-methoxyphenyl)diphenylphosphine oxide (3a). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3a (157.3 mg, 0.486 mmol, 97%) as a white solid. Melting Point: 156e157  C.5c 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.65 (s, 1H), 7.67e7.73 (m, 4H), 7.56e7.61 (m, 2H), 7.47e7.51 (m, 4H), 7.00e7.03 (m, 1H), 6.92e6.95 (m, 1H), 6.46e6.50 (m, 1H), 3.65 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.8 (d, 1J (C,P) ¼ 2.5 Hz), 151.9 (d, 1J (C,P) ¼ 15.2 Hz), 132.6 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 10.3 Hz), 131.5 (d, 1J (C,P) ¼ 104.6 Hz), 128.8 (d, 1J (C,P) ¼ 12.4 Hz), 120.5 (d, 1J (C,P) ¼ 2.4 Hz), 119.5 (d, 1J (C,P) ¼ 9.1 Hz), 116.1 (d, 1J (C,P) ¼ 11.4 Hz), 111.2 (d, 1J (C,P) ¼ 103.1 Hz), 55.8 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.0. 3.3.1.2. (5-ethoxy-2-hydroxyphenyl)diphenylphosphine oxide (3b). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3b (103.1 mg, 0.304 mmol, 61%) as a white solid. Melting Point: 196e197  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.66 (s, 1H), 7.67e7.73 (m, 4H), 7.56e7.61 (m, 2H), 7.46e7.52 (m, 4H), 6.99e7.02 (m, 1H), 6.90e6.94 (m, 1H), 6.46e6.50 (m, 1H), 3.82e3.87 (m, 2H), 1.31 (t, 1 J ¼ 16.0 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.8 (d, 1J (C,P) ¼ 1.5 Hz), 151.2 (d, 1J (C,P) ¼ 15.2 Hz), 132.6 (d, 1J (C,P) ¼ 2.6 Hz), 132.0 (d, 1J (C,P) ¼ 10.3 Hz), 131.5 (d, 1J (C,P) ¼ 104.4 Hz), 128.8 (d, 1J (C,P) ¼ 12.4 Hz), 121.3 (d, 1J (C,P) ¼ 2.3 Hz), 119.4 (d, 1J (C,P) ¼ 9.0 Hz), 116.9 (d, 1J (C,P) ¼ 11.1 Hz), 111.2 (d, 1J (C,P) ¼ 103.2 Hz), 64.2 (s), 14.8 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.1. HRMS (ESI) m/z: calcd. for C20H19O3P [MþH]þ: 339.1150, found: 329.1147. 3.3.1.3. (2-hydroxy-5-propoxyphenyl)diphenylphosphine oxide (3c). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3c (139.2 mg, 0.395 mmol, 79%) as a white solid. Melting Point: 193e195  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.67 (s, 1H), 7.67e7.73 (m, 4H), 7.55e7.60 (m, 2H), 7.46e7.50 (m, 4H), 6.99e7.02 (m, 1H), 6.47e6.52 (m, 1H), 3.73 (t, 1J ¼ 64 Hz, 2H), 1.67e1.72 (m, 2H), 1.95 (t, 1 J ¼ 6.4 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.7 (d, 1J (C,P) ¼ 2.5 Hz), 151.4 (d, 1J (C,P) ¼ 15.2 Hz), 132.6 (d, 1J (C,P) ¼ 2.7 Hz), 132.1 (d, 1J (C,P) ¼ 10 Hz), 132.0 (d, 1J (C,P) ¼ 103.4 Hz), 128.7 (d, 1J (C,P) ¼ 12.3 Hz), 121.4 (d, 1J (C,P) ¼ 2.4 Hz), 119.4 (d, 1J (C,P) ¼ 9.1 Hz), 116.8 (d, 1J (C,P) ¼ 11.0 Hz), 111.1 (d, 1J (C,P) ¼ 103.1 Hz), 70.2 (s), 22.5 (s), 14.8 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.0. HRMS (ESI) m/z: calcd. for C21H21O3P [MþH]þ: 353.1307, found: 353.1305.

27

3.3.1.4. (2-hydroxy-5-isopropoxyphenyl)diphenylphosphine oxide (3d). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3d (146.4 mg, 0.416 mmol, 83%) as a white solid. Melting Point: 213e215  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.67 (s, 1H), 7.67e7.72 (m, 4H), 7.56e7.60 (m, 2H), 7.46e7.51 (m, 4H), 6.99e7.02 (m, 1H), 6.90e6.93 (m, 1H), 6.46e6.51 (m, 1H), 4.23e4.29 (m, 1H), 1.20 (d, 1J ¼ 4.0 Hz, 6H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.9 (d, 1J (C,P) ¼ 2.4 Hz), 150.0 (d, 1J (C,P) ¼ 5.2 Hz), 132.6 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 10.4 Hz), 131.5 (d, 1J (C,P) ¼ 104.0 Hz), 128.7 (d, 1J (C,P) ¼ 12.4 Hz), 123.3 (d, 1J (C,P) ¼ 2.4 Hz), 119.5 (d, 1J (C,P) ¼ 9.1 Hz), 119.0 (d, 1J (C,P) ¼ 10.1 Hz), 111.2 (d, 1J (C,P) ¼ 103.1 Hz), 71.2 (s), 21.9 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.0. HRMS (ESI) m/z: calcd. for C21H21O3P [MþH]þ: 353.1307, found: 353.1305. 3.3.1.5. (5-allyl-2-hydroxy-3-methoxyphenyl)diphenylphosphine oxide (3e). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3e (160.2 mg, 0.441 mmol, 88%) as a light yellow solid. Melting Point: 101e103  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.74 (s, 1H), 7.67e7.73 (m, 4H), 7.55e7.59 (m, 2H), 7.45e7.50 (m, 4H), 6.82 (d, 1J ¼ 2.0 Hz, 1H), 6.45e6.49 (m, 1H), 5.80e5.90 (m, 1H), 4.97e5.04 (m, 2H), 3.88 (s, 3H), 3.22e3.25 (m, 2H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 151.7 (d, 1J (C,P) ¼ 3.4 Hz), 148.8 (d, 1J (C,P) ¼ 11.7 Hz), 137.1 (d, 1J (C,P) ¼ 0.1 Hz), 132.5 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 10.4 Hz), 131.8 (d, 1J (C,P) ¼ 104.7 Hz), 130.8 (d, 1J (C,P) ¼ 3.8 Hz), 128.6 (d, 1J (C,P) ¼ 12.4 Hz), 122.4 (d, 1J (C,P) ¼ 7.5 Hz), 116.1 (s), 115.9 (d, 1J (C,P) ¼ 2.3 Hz), 111.1 (d, 1J (C,P) ¼ 103.6 Hz), 56.0 (s), 39.6 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 38.6. HRMS (ESI) m/z: calcd. for C22H21O3P [MþH]þ: 365.1307, found: 365.1304. 3.3.1.6. (5-allyl-3-ethoxy-2-hydroxyphenyl)diphenylphosphine oxide (3f). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3f (136.1 mg, 0.360 mmol, 72%) as a light yellow solid. Melting Point: 114e117  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.51 (s, 1H), 7.68e7.73 (m, 4H), 7.55e7.59 (m, 2H), 7.45e7.50 (m, 4H), 6.80e6.83 (m, 1H), 6.48e6.52 (m, 1H), 5.80e5.90 (m, 1H), 4.96e5.04 (m, 2H), 4.07e4.12 (m, 2H), 3.22e3.24 (m, 2H), 1.46 (t, 1J ¼ 16.0 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 151.6 (d, 1J (C,P) ¼ 3.3 Hz), 148.0 (d, 1J (C,P) ¼ 11.7 Hz), 137.2 (s), 132.4 (d, 1J (C,P) ¼ 3.0 Hz), 132.0 (d, 1J (C,P) ¼ 10.5 Hz), 131.9 (d, 1J (C,P) ¼ 105.7 Hz), 130.7 (d, 1J (C,P) ¼ 13.9 Hz), 128.6 (d, 1J (C,P) ¼ 12.4 Hz), 127.8 (d, 1J (C,P) ¼ 2.7 Hz), 122.6 (d, 1J (C,P) ¼ 9.1 Hz), 117.1 (d, 1J (C,P) ¼ 2.4 Hz), 116.0 (s), 113.9 (d, 1J (C,P) ¼ 8.7 Hz), 111.5 (d, 1J (C,P) ¼ 102.4 Hz), 64.5 (s), 39.6 (s), 14.8 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 37.9. HRMS (ESI) m/z: calcd. for C23H23O3P [MþH]þ: 379.1463, found: 379.1460. 3.3.1.7. (5-allyl-2-hydroxy-3-isopropoxyphenyl)diphenylphosphine oxide (3g). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3g (170.2 mg, 0.434 mmol, 87%) as a light yellow solid. Melting Point: 122e124  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.14 (s, 1H), 7.68e7.74 (m, 4H), 7.54e7.58 (m, 2H), 7.45e7.49 (m, 4H), 6.85 (d, 1J ¼ 8 Hz, 1H), 6.54e6.58 (m, 1H), 5.80e5.90 (m, 1H), 4.96e5.04 (m, 2H), 4.54e4.60 (m, 1H), 3.21e3.23 (m, 2H), 1.37 (d, 1J ¼ 4.0 Hz, 6H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 152.1 (d, 1J (C,P) ¼ 3.4 Hz), 146.6 (d, 1J (C,P) ¼ 12.5 Hz), 137.2 (s), 132.3 (d, 1J (C,P) ¼ 2.9 Hz), 132.0 (d, 1J (C,P) ¼ 10.5 Hz), 132.0 (d, 1J (C,P) ¼ 104.6 Hz), 130.7 (d, 1J (C,P) ¼ 14.1 Hz), 128.6 (d, 1J (C,P) ¼ 12.4 Hz), 123.3 (d, 1J (C,P) ¼ 9.0 Hz), 120.0 (d, 1J (C,P) ¼ 1.5 Hz), 116.0 (s), 112.1 (d, 1J (C,P) ¼ 102.4 Hz), 71.6 (s), 39.5

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B. Xiong et al. / Journal of Organometallic Chemistry 885 (2019) 21e31

(s), 22.1 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 37.1. HRMS (ESI) m/z: calcd. for C24H25O3P [MþH]þ: 393.1620, found: 393.1657. 3.3.1.8. (3-chloro-2-hydroxy-5-methoxyphenyl)diphenylphosphine oxide (3h). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3h (123.9 mg, 0.347 mmol, 69%) as a light colorless oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 11.27 (s, 1H), 7.66e7.72 (m, 4H), 7.56e7.60 (m, 2H), 7.46e7.51 (m, 4H), 7.11e7.13 (m, 1H), 6.46e6.50 (m, 1H), 3.64 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 153.1 (d, 1J (C,P) ¼ 3.2 Hz), 151.7 (d, 1J (C,P) ¼ 13.9 Hz), 132.9 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 5.1 Hz), 130.8 (d, 1J (C,P) ¼ 105.5 Hz), 128.9 (d, 1J (C,P) ¼ 12.4 Hz), 123.4 (d, 1J (C,P) ¼ 13.1 Hz), 120.4 (d, 1J (C,P) ¼ 2.2 Hz), 115.6 (d, 1J (C,P) ¼ 10.8 Hz), 113.1 (d, 1J (C,P) ¼ 100.9 Hz), 56.0 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.3. HRMS (ESI) m/z: calcd. for C19H16ClO3P [MþH]þ: 359.0604, found: 359.0601. 3.3.1.9. (3-chloro-5-ethoxy-2-hydroxyphenyl)diphenylphosphine oxide (3i). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3i (109.7 mg, 0.295 mmol, 59%) as a light colorless oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 11.27 (s, 1H), 7.67e7.72 (m, 4H), 7.59e7.61 (m, 2H), 7.48e7.53 (m, 4H), 7.11e7.12 (m, 1H), 6.45e6.48 (m, 1H), 3.74 (t, 1J ¼ 12 Hz, 2H), 1.67e1.73 (m, 2H), 0.96 (t, 1 J ¼ 12.0 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 153.2 (d, 1J (C,P) ¼ 3.2 Hz), 150.9 (d, 1J (C,P) ¼ 17.0 Hz), 132.9 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 10.4 Hz), 130.9 (d, 1J (C,P) ¼ 105.4 Hz), 128.9 (d, 1J (C,P) ¼ 12.5 Hz), 123.4 (d, 1J (C,P) ¼ 13.1 Hz), 121.0 (d, 1J (C,P) ¼ 2.3 Hz), 116.3 (d, 1J (C,P) ¼ 10.8 Hz), 112.9 (d, 1J (C,P) ¼ 101.0 Hz), 64.4 (s), 14.7 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.4. HRMS (ESI) m/z: calcd. for C20H18ClO3P [MþH]þ: 373.0760, found: 373.0757. 3.3.1.10. (3-chloro-2-hydroxy-5-propoxyphenyl)diphenylphosphine oxide (3j). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3j (106.2 mg, 0.275 mmol, 55%) as a light red oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 11.26 (s, 1H), 7.67e7.72 (m, 4H), 7.58e7.62 (m, 2H), 7.48e7.52 (m, 4H), 7.11e7.13 (m, 1H), 6.47e6.52 (m, 1H), 3.83e3.88 (m, 2H), 1.32 (t, 1J ¼ 16 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 153.1 (d, 1J (C,P) ¼ 3.3 Hz), 151.2 (d, 1J (C,P) ¼ 17.0 Hz), 132.9 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 10.5 Hz), 130.9 (d, 1J (C,P) ¼ 105.4 Hz), 128.9 (d, 1J (C,P) ¼ 12.6 Hz), 123.3 (d, 1J (C,P) ¼ 13.2 Hz), 121.0 (d, 1J (C,P) ¼ 2.5 Hz), 116.1 (d, 1J (C,P) ¼ 10.9 Hz), 112.9 (d, 1J (C,P) ¼ 101.0 Hz), 70.5 (s), 22.4 (s), 10.4 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.4. HRMS (ESI) m/z: calcd. For C21H20ClO3P [MþH]þ: 387.0917, found: 387.0914. 3.3.1.11. (3-chloro-2-hydroxy-5-isopropoxyphenyl)diphenylphosphine oxide (3k). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 3k (121.1 mg, 0.313 mmol, 63%) as a light red oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 11.29 (s, 1H), 7.67e7.72 (m, 4H), 7.59e7.63 (m, 2H), 7.48e7.53 (m, 4H), 7.11e7.12 (m, 1H), 6.41e6.45 (m, 1H), 4.11e4.28 (m, 1H), 1.22 (t, 1J ¼ 12.0 Hz, 6H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 153.3 (d, 1J (C,P) ¼ 0.2 Hz), 149.7 (d, 1J (C,P) ¼ 17.0 Hz), 132.9 (d, 1J (C,P) ¼ 2.9 Hz), 132.0 (d, 1J (C,P) ¼ 10.4 Hz), 130.9 (d, 1J (C,P) ¼ 105.4 Hz), 128.8 (d, 1J (C,P) ¼ 12.5 Hz), 123.3 (d, 1J (C,P) ¼ 12.3 Hz), 123.0 (d, 1J (C,P) ¼ 2.3 Hz), 118.1 (d, 1J (C,P) ¼ 10.7 Hz), 112.8 (d, 1J (C,P) ¼ 100.9 Hz), 71.5 (s), 21.8 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.3. HRMS (ESI) m/z: calcd. for C21H20ClO3P [MþH]þ: 387.0917, found: 387.0915.

3.3.1.12. (2-hydroxy-5-methoxyphenyl)di-p-tolylphosphine oxide (4a). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4a (136.4 mg, 0.464 mmol, 93%) as a white solid. Melting Point: 197e198  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.72 (s, 1H), 7.55e7.60 (m, 4H), 7.27e7.30 (m, 4H), 6.89e7.00 (m, 2H), 6.45e6.49 (m, 1H), 3.64 (s, 3H), 2.40 (s, 6H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.7 (d, 1J (C,P) ¼ 2.5 Hz), 151.8 (d, 1J (C,P) ¼ 15.2 Hz), 143.2 (d, 1J (C,P) ¼ 2.8 Hz), 132.0 (d, 1J (C,P) ¼ 10.8 Hz), 129.5 (d, 1J (C,P) ¼ 12.8 Hz), 128.4 (d, 1J (C,P) ¼ 107.0 Hz), 120.3 (d, 1J (C,P) ¼ 2.3 Hz), 119.3 (d, 1J (C,P) ¼ 9.0 Hz), 116.2 (d, 1J (C,P) ¼ 10.9 Hz), 111.8 (d, 1J (C,P) ¼ 103.0 Hz), 55.8 (s), 21.7 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.2. HRMS (ESI) m/z: calcd. for C21H21O3P [MþH]þ: 353.1307, found: 353.1304. 3.3.1.13. (2-hydroxy-5-methoxyphenyl)di-m-tolylphosphine oxide (4b). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4b (124.9 mg, 0.465 mmol, 85%) as a white solid. Melting Point: 225e227  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.68 (s, 1H), 7.55e7.58 (m, 2H), 7.35e7.45 (m, 6H), 6.99e7.02 (m, 1H), 6.91e6.94 (m, 1H), 6.47e6.52 (m, 1H), 3.65 (s, 3H), 2.37 (s, 6H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.8 (d, 1J (C,P) ¼ 2.5 Hz), 151.8 (d, 1J (C,P) ¼ 15.1 Hz), 138.8 (d, 1J (C,P) ¼ 12.3 Hz), 133.4 (d, 1J (C,P) ¼ 2.9 Hz), 132.4 (d, 1J (C,P) ¼ 9.9 Hz), 131.4 (d, 1J (C,P) ¼ 104.0 Hz), 129.1 (d, 1J (C,P) ¼ 10.7 Hz), 128.5 (d, 1J (C,P) ¼ 13.1 Hz), 120.3 (d, 1J (C,P) ¼ 2.3 Hz), 119.4 (d, 1J (C,P) ¼ 8.9 Hz), 116.3 (d, 1J (C,P) ¼ 10.2 Hz), 111.6 (d, 1J (C,P) ¼ 102.7 Hz), 55.8 (s), 21.5 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.4. HRMS (ESI) m/z: calcd. for C21H21O3P [MþH]þ: 353.1307, found: 353.1304. 3.3.1.14. bis(3,5-dimethylphenyl)(2-hydroxy-5-methoxyphenyl)phosphine oxide (4c). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4c (164.8 mg, 0.433 mmol, 87%) as a white solid. Melting Point: 248e251  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.74 (s, 1H), 7.19e7.30 (m, 6H), 6.90e7.01 (m, 2H), 6.49e6.53 (m, 1H), 3.67 (s, 3H), 2.32 (s, 12H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.7 (d, 1J (C,P) ¼ 2.3 Hz), 151.8 (d, 1J (C,P) ¼ 15.0 Hz), 138.5 (d, 1J (C,P) ¼ 11.9 Hz), 134.3 (d, 1J (C,P) ¼ 2.9 Hz), 131.3 (d, 1J (C,P) ¼ 103.5 Hz), 129.5 (d, 1J (C,P) ¼ 10.2 Hz), 120.1 (d, 1J (C,P) ¼ 2.4 Hz), 119.3 (d, 1J (C,P) ¼ 8.9 Hz), 116.6 (d, 1J (C,P) ¼ 11.1 Hz), 111.8 (d, 1J (C,P) ¼ 102.0 Hz), 55.8 (s), 21.4 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.7. HRMS (ESI) m/z: calcd. for C23H25O3P [MþH]þ: 381.1620, found: 381.1617. 3.3.1.15. (2-hydroxy-5-methoxyphenyl)bis(4-methoxyphenyl)phosphine oxide (4d). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4d (149.9 mg, 0.391 mmol, 78%) as a light yellow solid. Melting Point: 113e115  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.80 (s, 1H), 7.58e7.64 (m, 4H), 6.90e7.01 (m, 6H), 6.43e6.47 (m, 1H), 3.86 (s, 6H), 3.66 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 162.9 (d, 1J (C,P) ¼ 2.7 Hz), 157.7 (d, 1J (C,P) ¼ 2.6 Hz), 151.8 (d, 1J (C,P) ¼ 5.2 Hz), 134.0 (d, 1J (C,P) ¼ 11.7 Hz), 123.4 (d, 1J (C,P) ¼ 110.2 Hz), 120.1 (d, 1J (C,P) ¼ 2.4 Hz), 119.3 (d, 1J (C,P) ¼ 9.1 Hz), 116.2 (d, 1J (C,P) ¼ 11.2 Hz), 114.2 (d, 1J (C,P) ¼ 13.5 Hz), 112.3 (d, 1J (C,P) ¼ 103.8 Hz), 55.8 (s), 55.4 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 38.8. HRMS (ESI) m/z: calcd. for C21H21O5P [MþH]þ: 385.1205, found: 385.1202. 3.3.1.16. (2-hydroxy-5-methoxyphenyl)bis(4-(trifluoromethyl) phenyl)phosphine oxide (4e). According to the general procedure,

B. Xiong et al. / Journal of Organometallic Chemistry 885 (2019) 21e31

work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4e (158.9 mg, 0.346 mmol, 69%) as a light yellow solid. Melting Point: 197e198  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.14 (s, 1H), 7.79e7.84 (m, 4H), 7.71e7.74 (m, 4H), 7.03e7.06 (m, 1H), 6.94e6.98 (m, 1H), 6.60e6.65 (m, 1H), 3.68 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 156.8 (d, 1J (C,P) ¼ 2.8 Hz), 152.4 (d, 1J (C,P) ¼ 15.3 Hz), 135.3 (d, 1J (C,P) ¼ 103.2 Hz), 134.6 (d, 1J (C,P) ¼ 2.9 Hz), 134.3 (d, 1J (C,P) ¼ 2.9 Hz), 132.4 (d, 1J (C,P) ¼ 10.8 Hz), 125.7 (m), 123.3 (d, 1J (C,P) ¼ 271 Hz), 121.4 (d, 1J (C,P) ¼ 2.5 Hz), 119.6 (m), 116.0 (d, 1J (C,P) ¼ 10.6 Hz), 110.5 (d, 1J (C,P) ¼ 105.5 Hz), 55.8 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 34.9. 19F NMR (376 MHz, CDCl3, 25  C): d ¼ 63.3. HRMS (ESI) m/z: calcd. for C21H15F6O3P [MþH]þ: 461.0741, found: 461.0738. 3.3.1.17. (2-hydroxy-5-methoxyphenyl)di(naphthalen-2-yl)phosphine oxide (4f). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4f (152.6 mg, 0.360 mmol, 72%) as a light yellow solid. Melting Point: 245e247  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.74 (s), 8.28e8.32 (m, 2H), 7.86e7.96 (m, 6H), 7.69e7.74 (m, 2H), 7.60e7.64 (m, 2H), 7.54e7.58 (m, 2H), 6.96e7.06 (m, 2H), 6.59e6.63 (m, 2H), 3.63 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.9 (d, 1J (C,P) ¼ 2.4 Hz), 152.0 (d, 1J (C,P) ¼ 15.3 Hz), 135.0 (d, 1J (C,P) ¼ 2.3 Hz), 134.3 (d, 1J (C,P) ¼ 10.1 Hz), 132.4 (d, 1J (C,P) ¼ 13.6 Hz), 129.1 (d, 1J (C,P) ¼ 0.5 Hz), 128.8 (s), 128.7 (d, 1J (C,P) ¼ 1.4 Hz), 128.5 (d, 1J (C,P) ¼ 105.2 Hz), 127.9 (d, 1J (C,P) ¼ 0.3 Hz), 127.2 (d, 1J (C,P) ¼ 0.3 Hz), 126.5 (d, 1J (C,P) ¼ 10.8 Hz), 120.7 (d, 1J (C,P) ¼ 2.5 Hz), 119.6 (d, 1J (C,P) ¼ 9.1 Hz), 116.3 (d, 1J (C,P) ¼ 11.2 Hz), 111.4 (d, 1J (C,P) ¼ 103.4 Hz), 55.9 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 39.3. HRMS (ESI) m/z: calcd. for C27H21O3P [MþH]þ: 425.1307, found: 425.1305. 3.3.1.18. (2-hydroxy-5-methoxyphenyl)di(naphthalen-1-yl)phosphine oxide (4g). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4g (135.9 mg, 0.321 mmol, 64%) as a light yellow solid. Melting Point: 228e230  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.89 (s, 1H), 8.76 (s, 2H), 8.05e8.08 (m, 2H), 7.93e7.96 (m, 2H), 7.52e7.58 (m, 4H), 7.37 (s, 4H), 7.03e7.05 (m, 2H), 6.18e6.22 (m, 1H), 3.51 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 158.1 (d, 1J (C,P) ¼ 2.6 Hz), 151.8 (d, 1J (C,P) ¼ 15.4 Hz), 134.1 (d, 1J (C,P) ¼ 9.1 Hz), 133.9 (d, 1J (C,P) ¼ 3.0 Hz), 133.6 (d, 1J (C,P) ¼ 8.1 Hz), 133.4 (d, 1J (C,P) ¼ 12.5 Hz), 129.0 (d, 1J (C,P) ¼ 1.0 Hz), 127.8 (d, 1J (C,P) ¼ 0.3 Hz), 127.5 (d, 1J (C,P) ¼ 102.8 Hz), 127.4 (d, 1J (C,P) ¼ 4 Hz), 126.8 (s), 124.3 (d, 1J (C,P) ¼ 15.3 Hz), 120.7 (d, 1J (C,P) ¼ 2.3 Hz), 119.7 (d, 1J (C,P) ¼ 9.0 Hz), 116.5 (d, 1J (C,P) ¼ 11.2 Hz), 111.3 (d, 1J (C,P) ¼ 103.8 Hz), 55.6 (s). 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 48.6. HRMS (ESI) m/z: calcd. for C27H21O3P [MþH]þ: 425.1307, found: 425.1305. 3.3.1.19. 6-(2-hydroxy-5-methoxyphenyl)-6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide (4h). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 4h (44.1 mg, 0.131 mmol, 26%) as a light yellow solid. Melting Point: 97e98  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 10.32 (s, 1H), 8.03e8.10 (m, 2H), 7.66e7.76 (m, 2H), 7.41e7.50 (m, 2H), 7.06e7.09 (m, 2H), 6.97e7.01 (m, 1H), 6.38e6.43 (m, 1H), 3.56 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.3 (d, 1J (C,P) ¼ 5.1 Hz), 152.2 (d, 1J (C,P) ¼ 16.8 Hz), 148.9 (d, 1J (C,P) ¼ 8.5 Hz), 135.6 (d, 1J (C,P) ¼ 5.8 Hz), 133.7 (d, 1J (C,P) ¼ 2.5 Hz), 131.3 (d, 1J (C,P) ¼ 12.7 Hz), 130.8 (s), 128.6 (d, 1J (C,P) ¼ 14.6 Hz), 125.8 (d, 1J (C,P) ¼ 3.3 Hz), 124.6 (s), 123.6 (d, 1J (C,P) ¼ 10.0 Hz), 121.4 (d, 1J (C,P) ¼ 11.2 Hz), 120.7 (d, 1J (C,P) ¼ 6.2 Hz), 116.6 (d, 1J (C,P) ¼ 236 Hz), 114.9 (d, 1J (C,P) ¼ 11.0 Hz), 109.2 (d, 1J

(C,P) ¼ 143.3 Hz), 55.8 (s).

29 31

P NMR (160 MHz, CDCl3, 25  C):

d ¼ 32.8. HRMS (ESI) m/z: calcd. for C19H15O4P [MþH]þ: 339.0786, found: 339.0783. 3.3.1.20. 6-(4-methoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5a). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5a (145.2 mg, 0.451 mmol, 90%) as a colorless solid. Melting Point: 85e88  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.94e8.02 (m, 3H), 7.72e7.76 (m, 1H), 7.49e7.54 (m, 1H), 7.38e7.42 (m, 1H), 7.22e7.32 (m, 2H), 6.92e6.96 (m, 2H), 6.73e6.77 (m, 2H), 3.73 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 156.9 (d, 1J (C,P) ¼ 1.5 Hz), 150.0 (d, 1J (C,P) ¼ 8.2 Hz), 143.2 (d, 1J (C,P) ¼ 8.6 Hz), 137.1 (d, 1J (C,P) ¼ 7.0 Hz), 133.9 (d, 1J (C,P) ¼ 2.5 Hz), 130.8 (d, 1J (C,P) ¼ 9.2 Hz), 130.7 (s), 128.3 (d, 1J (C,P) ¼ 15.5 Hz), 125.3 (d, 1J (C,P) ¼ 1.4 Hz), 125.0 (s), 124.1 (d, 1J (C,P) ¼ 12.3 Hz), 122.5 (d, 1J (C,P) ¼ 0.6 Hz), 121.7 (d, 1J (C,P) ¼ 191.1 Hz), 121.6 (d, 1J (C,P) ¼ 4.1 Hz), 120.3 (d, 1J (C,P) ¼ 6.7 Hz), 114.6 (d, 1J (C,P) ¼ 1.7 Hz), 55.6 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 6.8. HRMS (ESI) m/z: calcd. for C19H15O4P [MþH]þ: 339.0786, found: 339.0783. 3.3.1.21. 6-(4-ethoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5b). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5b (128.3 mg, 0.382 mmol, 76%) as a white solid. Melting Point: 99e101  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.94e8.02 (m, 3H), 7.70e7.76 (m, 1H), 7.49e7.53 (m, 1H), 7.38e7.45 (m, 1H), 7.29e7.35 (m, 1H), 7.22e7.28 (m, 1H), 6.90e6.94 (m, 2H), 6.72e6.76 (m, 2H), 3.92e3.97 (m, 2H), 3.37(t, 1J ¼ 12 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 156.3 (d, 1J (C,P) ¼ 1.1 Hz), 150.0 (d, 1J (C,P) ¼ 8.3 Hz), 143.1 (d, 1J (C,P) ¼ 8.6 Hz), 137.1 (d, 1J (C,P) ¼ 6.9 Hz), 133.9 (d, 1J (C,P) ¼ 2.5 Hz), 130.8 (d, 1J (C,P) ¼ 9.2 Hz), 130.6 (s), 128.4 (s), 128.2 (s), 125.3 (d, 1J (C,P) ¼ 1.3 Hz), 125.0 (s), 124.1 (d, 1J (C,P) ¼ 12.3 Hz), 122.5 (d, 1J (C,P) ¼ 2.2 Hz), 121.7 (d, 1J (C,P) ¼ 111.2 Hz), 121.6 (d, 1J (C,P) ¼ 4.1 Hz), 120.3 (d, 1J (C,P) ¼ 6.9 Hz), 115.2 (d, 1J (C,P) ¼ 0.9 Hz), 63.8 (s), 14.8 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 6.8. HRMS (ESI) m/z: calcd. for C20H17O4P [MþH]þ: 353.0943, found: 353.0940. 3.3.1.22. 6-(4-ethoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5c). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5c (143.6 mg, 0.411 mmol, 82%) as a white solid. Melting Point: 116e118  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.94e8.02 (m, 3H), 7.71e7.75 (m, 1H), 7.48e7.53 (m, 1H), 7.37e7.42 (m, 1H), 7.22e7.31 (m, 2H), 6.91e6.93 (m, 2H), 6.73e6.75 (m, 2H), 3.83 (t, 1 J ¼ 12 Hz, 2H), 1.73e1.78 (m, 2H), 1.00 (t, 1J ¼ 12 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 156.5 (d, 1J (C,P) ¼ 2 Hz), 150.0 (d, 1 J (C,P) ¼ 8 Hz), 143.0 (d, 1J (C,P) ¼ 8 Hz), 137.1 (d, 1J (C,P) ¼ 7 Hz), 133.8 (d, 1J (C,P) ¼ 3 Hz), 130.8 (d, 1J (C,P) ¼ 9 Hz), 130.6 (s), 128.3 (d, 1 J (C,P) ¼ 16 Hz), 125.3 (d, 1J (C,P) ¼ 1 Hz), 125.0 (s), 124.1 (d, 1J (C,P) ¼ 12 Hz), 122.5 (d, 1J (C,P) ¼ 4 Hz), 121.5 (d, 1J (C,P) ¼ 188 Hz), 121.5 (d, 1J (C,P) ¼ 4 Hz), 120.3 (d, 1J (C,P) ¼ 7 Hz), 115.2 (d, 1J (C,P) ¼ 2 Hz), 69.9 (s), 22.5 (s), 10.5 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 6.8. HRMS (ESI) m/z: calcd. for C21H19O4P [MþH]þ: 367.1099, found: 367.1096. 3.3.1.23. 6-(4-isopropoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5d). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5d (148.8 mg, 0.425 mmol, 85%) as a white solid. Melting Point: 102e105  C. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.94e8.04 (m, 3H), 7.72e7.77 (m, 1H), 7.49e7.54 (m, 1H), 7.37e7.42 (m, 1H), 7.22e7.31 (m, 2H), 6.89e6.94 (m, 2H), 6.71e6.77 (m, 2H), 4.39e4.45 (m, 1H), 1.28 (d, 1J ¼ 8.0 Hz, 6H); 13C NMR (100 MHz, CDCl3, 25  C,

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TMS): d ¼ 155.2 (d, 1J (C,P) ¼ 1.4 Hz), 150.0 (d, 1J (C,P) ¼ 8.2 Hz), 143.0 (d, 1J (C,P) ¼ 8.6 Hz), 137.2 (d, 1J (C,P) ¼ 7.0 Hz), 133.9 (d, 1J (C,P) ¼ 2.5 Hz), 130.8 (d, 1J (C,P) ¼ 8.2 Hz), 130.6 (s), 128.3 (d, 1J (C,P) ¼ 15.6 Hz), 125.3 (d, 1J (C,P) ¼ 1.3 Hz), 125.0 (s), 124.2 (d, 1J (C,P) ¼ 12.1 Hz), 122.5 (d, 1J (C,P) ¼ 2.6 Hz), 121.7 (d, 1J (C,P) ¼ 189.6 Hz), 121.6 (d, 1J (C,P) ¼ 4.0 Hz), 120.3 (d, 1J (C,P) ¼ 6.9 Hz), 116.2 (d, 1J (C,P) ¼ 1.3 Hz), 70.5 (s), 22.0 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 6.8. HRMS (ESI) m/z: calcd. for C21H19O4P [MþH]þ: 367.1099, found: 367.1097. 3.3.1.24. 6-(2-chloro-4-methoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5e). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5e (140.6 mg, 0.395 mmol, 79%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.94e8.06 (m, 3H), 7.73e7.77 (m, 1H), 7.49e7.54 (m, 1H), 7.38e7.42 (m, 1H), 7.24e7.33 (m, 3H), 6.71e6.81 (m, 2H), 3.73 (s, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 157.0 (d, 1J (C,P) ¼ 1.6 Hz), 149.9 (d, 1J (C,P) ¼ 8.3 Hz), 139.5 (d, 1J (C,P) ¼ 8.4 Hz), 137.3 (d, 1J (C,P) ¼ 7.3 Hz), 134.0 (d, 1J (C,P) ¼ 2.5 Hz), 130.8 (d, 1J (C,P) ¼ 9.3 Hz), 130.6 (s), 128.3 (d, 1J (C,P) ¼ 15.7 Hz), 126.4 (d, 1J (C,P) ¼ 5.7 Hz), 125.3 (d, 1J (C,P) ¼ 1.3 Hz), 124.1 (d, 1J (C,P) ¼ 12.4 Hz), 122.9 (d, 1J (C,P) ¼ 2.8 Hz), 122.5 (d, 1J (C,P) ¼ 12.1 Hz), 121.3 (d, 1J (C,P) ¼ 180.6 Hz), 120.3 (d, 1J (C,P) ¼ 6.9 Hz), 115.5 (d, 1J (C,P) ¼ 0.9 Hz), 113.3 (d, 1J (C,P) ¼ 1.8 Hz), 55.8 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 7.3. HRMS (ESI) m/z: calcd. for C19H14ClO4P [MþH]þ: 373.0396, found: 373.0393. 3.3.1.25. 6-(2-chloro-4-ethoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5f). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5f (133.4 mg, 0.362 mmol, 72%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.95e8.06 (m, 3H), 7.73e7.78 (m, 1H), 7.50e7.55 (m, 1H), 7.38e7.43 (m, 1H), 7.25e7.32 (m, 3H), 6.70e6.80 (m, 2H), 3.91e3.96 (m, 2H), 1.37 (d, 1J ¼ 16.2 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 156.4 (d, 1J (C,P) ¼ 1.6 Hz), 149.9 (d, 1J (C,P) ¼ 8.3 Hz), 139.4 (d, 1J (C,P) ¼ 8.4 Hz), 137.3 (d, 1J (C,P) ¼ 7.3 Hz), 134.0 (d, 1J (C,P) ¼ 2.5 Hz), 130.9 (d, 1J (C,P) ¼ 9.3 Hz), 130.6 (s), 128.4 (s), 128.2 (s), 126.3 (d, 1J (C,P) ¼ 5.7 Hz), 125.3 (d, 1J (C,P) ¼ 1.3 Hz), 124.1 (d, 1J (C,P) ¼ 12.4 Hz), 122.9 (d, 1J (C,P) ¼ 2.8 Hz), 122.6 (d, 1J (C,P) ¼ 12.1 Hz), 121.4 (d, 1J (C,P) ¼ 180.6 Hz), 120.4 (d, 1J (C,P) ¼ 6.9 Hz), 116.1 (d, 1J (C,P) ¼ 0.9 Hz), 113.8 (d, 1J (C,P) ¼ 1.7 Hz), 64.1 (s), 14.1 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 7.3. HRMS (ESI) m/z: calcd. for C20H16ClO4P [MþH]þ: 387.0553, found: 387.0550. 3.3.1.26. 6-(2-chloro-4-propoxyphenoxy)-6H-dibenzo[c,e][1,2]oxaphosphinine (5g). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5g (132.5 mg, 0.345 mmol, 69%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.95e8.06 (m, 3H), 7.74e7.78 (m, 1H), 7.50e7.55 (m, 1H), 7.38e7.43 (m, 1H), 7.25e7.32 (m, 3H), 6.80e6.81 (m, 1H), 6.70e6.74 (m, 1H), 3.83 (t, 1J ¼ 12.0 Hz, 2H), 1.72e1.81 (m, 2H), 1.00 (t, 1J ¼ 16 Hz, 3H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 156.6 (d, 1J (C,P) ¼ 1.3 Hz), 149.9 (d, 1J (C,P) ¼ 8.4 Hz), 139.3 (d, 1J (C,P) ¼ 8.4 Hz), 137.3 (d, 1J (C,P) ¼ 7.2 Hz), 134.0 (d, 1J (C,P) ¼ 2.5 Hz), 130.9 (d, 1J (C,P) ¼ 9.4 Hz), 130.6 (s), 128.3 (d, 1J (C,P) ¼ 15.7 Hz), 126.3 (d, 1J (C,P) ¼ 5.5 Hz), 125.3 (s), 125.0 (s), 124.1 (d, 1J (C,P) ¼ 12.3 Hz), 122.8 (d, 1J (C,P) ¼ 2.8 Hz), 122.4 (d, 1J (C,P) ¼ 18.6 Hz), 121.5 (d, 1J (C,P) ¼ 211.3 Hz), 116.1 (d, 1J (C,P) ¼ 0.9 Hz), 113.8(d, 1J (C,P) ¼ 1.8 Hz), 76.7 (s), 22.4 (s), 10.5 (s); 31 P NMR (160 MHz, CDCl3, 25  C): d ¼ 7.3. HRMS (ESI) m/z: calcd. for C21H18ClO4P [MþH]þ: 401.0709, found: 401.0706.

3.3.1.27. 6-(2-chloro-4-isopropoxyphenoxy)-6H-dibenzo[c,e][1,2] oxaphosphinine (5h). According to the general procedure, work-up and flash column chromatography (Hexane/EtOAc: 2:1) gave product 5h (140.2 mg, 0.365 mmol, 73%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25  C, TMS): d ¼ 7.95e8.07 (m, 3H), 7.74e7.78 (m, 1H), 7.50e7.55 (m, 1H), 7.38e7.43 (m, 1H), 7.25e7.32 (m, 3H), 6.79e6.81 (m, 1H), 6.69e6.72 (m, 1H), 4.39e4.45 (m, 1H), 1.29 (d, 1 J ¼ 8.0 Hz, 6H); 13C NMR (100 MHz, CDCl3, 25  C, TMS): d ¼ 155.4 (d, 1J (C,P) ¼ 1.5 Hz), 149.9 (d, 1J (C,P) ¼ 8.3 Hz), 139.3 (d, 1J (C,P) ¼ 8.7 Hz), 137.3 (d, 1J (C,P) ¼ 7.2 Hz), 134.0 (d, 1J (C,P) ¼ 2.6 Hz), 130.9 (d, 1J (C,P) ¼ 9.2 Hz), 130.6 (s), 128.3 (d, 1J (C,P) ¼ 15.8 Hz), 126.3 (d, 1J (C,P) ¼ 5.8 Hz), 125.3 (s), 125.0 (s), 124.1 (d, 1J (C,P) ¼ 13.4 Hz), 122.8 (d, 1J (C,P) ¼ 2.9 Hz), 122.4 (d, 1J (C,P) ¼ 18.0 Hz), 121.4 (d, 1J (C,P) ¼ 180.9 Hz), 120.3 (d, 1J (C,P) ¼ 6.9 Hz), 117.6 (d, 1J (C,P) ¼ 0.9 Hz), 115.1 (d, 1J (C,P) ¼ 1.8 Hz), 76.7 (s), 21.9 (s); 31P NMR (160 MHz, CDCl3, 25  C): d ¼ 7.3. HRMS (ESI) m/z: calcd. for C21H18ClO4P [MþH]þ: 401.0709, found: 401.0706. Acknowledgments This work was supported by National Natural Science Foundation of China (21606080), Scientific Research Fund of Hunan Provincial Education Department (16B111). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jorganchem.2018.12.020. References [1] a) L.D. Quin (Ed.), A Guide to Organophosphorus Chemistry, Wiley, New York, 2000; b) F. Palacios, C. Alonso, J.M. Santos, Chem. Rev. 105 (2005) 899e932; c) A. Sakakura, A. Ukai, K. Ishihara, Nature 445 (2007) 900e903; d) T.H. Lee, C.K. Lee, W.L. Tsou, S.Y. Liu, M.T. Kuo, W.C. Wen, Planta Med. 73 (2007) 1412e1415; e) S. Vassiliou, A. Grabowiecka, P. Kosikowska, A. Yiotakis, P. Kafarski, Ł. Berlicki, J. Med. Chem. 51 (2008) 5736e5744; f) D. Gilheany (Ed.), Novel Organophosphorus Compounds for Materials and Organic Synthesis, 2017. Uppsala; g) P.S. Hammond, J.S. Forster, C.N. Lieske, H.D. Durst, J. Am. Chem. Soc. 111 (1989) 7860e7866; h) X.-S. Li, Y.-P. Han, X.-Y. Zhu, M. Li, W.-X. Wei, Y.-M. Liang, J. Org. Chem. 82 (2017) 11636e11643; i) L. Li, J.-J. Wang, G.-W. Wang, J. Org. Chem. 81 (2016) 5433e5439; j) N. Tian, X. Wen, J. Gong, L. Ma, J. Xue, T. Tang, Polym. Adv. Technol. 24 (2013) 653e659; k) R. Schmutzler, Angew. Chem. Int. Ed. 28 (1989) 1716e1717;
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