A deep feature mining method of electronic nose sensor data for identifying beer olfactory information

DOI: 10.1002/ejoc.201900706

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Cyclic N-Sulfonamide

B(C6F5)3-Catalyzed Reduction of Cyclic N-Sulfonyl Ketimines Lei Shi,*[a] Robert Li-Yuan Bao,[a] Limin Zheng,[a] and Rong Zhao [a] Abstract: A metal-free method for reduction of cyclic N-sulfonyl ketimines catalyzed by B(C6F5)3, using commercially available methylphenylsilane as a reducing reagent under mild conditions has been developed. This reductive protocol was effec-

tive, not only providing the expected cyclic N-sulfonamides in good to excellent yields, but also showing good functionalgroup tolerance.

Introduction

H2.[12,14–18] In 2000, Piers reported an effective hydrosilation of benzaldimines and ketimines which was catalyzed by B(C6F5)3 in presence of PhMe2SiH for the first time.[19] From then on, the system of silane and B(C6F5)3 has been utilized to reduce the substituted indoles,[15] quinolines[16] and pyridines gradually.[20] Actually, the basic conception of Lewis acid–base interaction has also rooted in other fields of chemistry. In a similar fashion, Ishihara has obtained some remarkable consequences in cooperative catalysis and asymmetric supramolecular methodology, in which the electrophilic boron center plays a key role in the Lewis acid-assisted Brønsted acid catalysts and the artificial enzyme-like supramolecular catalysts via the Lewis acid–base interaction.[21] Compounds containing a cyclic N-sulfonylamide moiety may have various biological activities, such as potential modulator of neurotransmitter, inhibitor of carbonic anhydrase, HIV protease inhibitor and so on (Figure 1).[22] On the other hand, the cyclic

Recently, boron catalysis has attracted significant attention since the frustrated Lewis pairs (FLPs) achieved great progress in the field of metal-free catalysis and activation of small molecules.[1,2] Indeed, that organic boron catalysts, usually combining low cost and low toxicity with an enhanced stability to moisture and air, can circumvent classical drawbacks of many metallic catalysts.[3] For example, while Stephan reported metalfree reductions of N-heterocycles via FLPs for the first time in 2010,[4] Du described the hydrogenations of unsaturated nitrogen-containing compounds in 2013.[5–8] The feasibility of FLPs systems to activate H2 and to hydrogenate unsaturated substrates, particularly heteroaromatic rings, has been examined.[9–13] As an alternative to H2 in the reduction, hydrosilanes always turn out to be more convenient and variable. In fact, the FLPs can also activate the Si–H bond apart from activating the

Figure 1. Selected examples of biologically active compounds, chiral auxiliary and chiral ligands. [a] School of Science, Harbin Institute of Technology, Shenzhen 518055, China E-mail: [email protected] http://homepage.hit.edu.cn/shilei Supporting information and ORCID(s) from the author(s) for this article are available on the WWW under https://doi.org/10.1002/ejoc.201900706. Eur. J. Org. Chem. 2019, 6550–6556

N-sulfonylamides are highly valuable synthons. In earlier study of the cyclic N-sulfonylamides, they were used as the chiral benzosultam auxiliaries (Figure 1) in the asymmetric alkylations, acylations and aldolizations.[23] Similarly, this strategy was employed to prepare the enantiomerically unnatural aryl glycinols

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Full Paper and aryl glycines in Kim's research.[24] Moreover, cyclic N-sulfonylamides have been used as key scaffolds to prepare the ligands (Figure 1) in the ruthenium(II)-catalyzed asymmetric dynamic kinetic resolutions.[25] Recently, Xu had a breakthrough on asymmetric arylation of cyclic ketimines[26] and cyclic diketimines[27] with using Rh as a catalyst. As for the synthesis of cyclic N-sulfonylamides, a series of asymmetric hydrogenation of cyclic N-sulfonyl ketimines catalyzed by palladium have been reported by zhou[28] and zhang.[29] In 2015, Zhou described an asymmetric transfer hydrogenation of cyclic N-sulfonyl ketimines in the presence of nickel catalyst.[30] In addition, the synthetic strategies of palladium-catalyzed intramolecular asymmetric reductive amination[31] and Rh-catalyzed C–H olefination[32] have also been applied for the synthesis of cyclic Nsulfonylamides. Comparatively speaking, the metal-catalyzed protocols dominated the synthesis of cyclic N-sulfonylamides. Here we describe a metal-free B(C6F5)3-catalyzed method as an alternative approach to prepare the cyclic N-sulfonylamides. We hope the method could promote the development of preparing structurally diverse and complex cyclic N-sulfonylamides with biologically activities or other functionalities.

Results and Discussion We began our investigation with reducing the 3-methylbenzo[d]isothiazole-1,1-dioxide 1a by using methylphenylsilane and catalytic amount of B(C6F5)3. To our delight, we obtained the expected 3-methyl-2,3- dihydrobenzo[d]isothiazole-1,1-dioxide 2a with the yield of 95 % in dry dichloromethane at room temperature (Table 1, entry 1). We further devoted our efforts to increase the yield by screening the solvents, tuning the kinds of hydrogen sources and the amount of methylphenylsilane. Here the results were summarized in Table 1. Then, we screened the typical solvents as showed in Table 1, entries 1–6. To our surprise, it gave a very satisfactory conversion with using toluene as solvent in the presence of methylphenylsilane (4 equiv.) at room temperature for 24 h (Table 1, entry 6). It was found that the solvent effect did play a very significant role in the reaction. After confirming toluene as solvent, we explored different kinds of reducing reagents. As shown in Table 1, when the ammonia borane 3c served as hydride donor, the yield of 2a reduced to 95 % (Table 1, entry 8) because of the poor solubility of 3c. Again, similar results were obtained with using phenylsilane 3b as the reductant (Table 1, entry 7). To our disappointment, when diethyl-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate 3d was selected as the reductant for the reaction, no target product was observed (Table 1, entry 9). We anticipated that higher temperature would be necessary to facilitate hydride abstraction, but 3d turned out to be reluctant to react at 60 °C. Up to this point, the data disclosed that methylphenylsilane could be selected as the reducing reagent in subsequent studies. Next, we also tested the amount of methylphenylsilane (Table 1, entries 6, 10–12) and the results showed that methylphenylsilane (1.1 equiv.) was the minimal amount for the reaction (Table 1, entry 12). As a comparison, the reductive reaction was performed in the absence of B(C6F5)3 resulting in a yield of Eur. J. Org. Chem. 2019, 6550–6556

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Table 1. Optimization of the reaction conditions.[a]

Entry

Hydrogen source (equiv.)

Solvent

Yield [%][b]

1 2 3 4 5 6 7 8 9 10 11 12 13[c] 14[d]

3a (4.0) 3a (4.0) 3a (4.0) 3a (4.0) 3a (4.0) 3a (4.0) 3b (4.0) 3c (4.0) 3d (4.0) 3a (2.0) 3a (1.5) 3a (1.1) 3a (1.1) H2

DCM DCE dioxane hexane iPrOH toluene toluene toluene toluene toluene toluene toluene toluene toluene

95 95 94 86 77 99 95 95 N.R. 99 99 99 9 N.R.

[a] Conditions: 1a (0.2 mmol), B(C6F5)3 (5.0 mol %), solvent (2.0 mL), 25 °C, 24 h. [b] Isolated yields. [c] No B(C6F5)3. [d] The reaction was carried out in toluene under H2 (1 atm.). DCM = Dichloromethane, DCE = 1,2-Dichloroethane. N.R. = No Reaction.

9 % (Table 1, entry 13), in which the B(C6F5)3 has proved to be a critical factor for the reductive transformation. Finally, we tried to use 1 atm of H2 as the reductant directly. But unfortunately, it was failed to reduce the ketimine 1a. In summary, the conditions of entry 12 in Table 1 were the best options. With the optimized reaction conditions in hand, a variety of cyclic N-sulfonyl ketimines 1 were subjected to the reduction. As shown in Table 2, it was pleased to find that all these reactions proceeded smoothly to afford the corresponding products in good to excellent yields. Gratifyingly, ketimines both containing electron-donating and electron-withdrawing groups were tolerated under the current reaction conditions. For example, ketimine 1i (R = (4-methoxy)phenyl) gave the corresponding product 2i in 76 % yield; Meanwhile, both 1p (R = (3,5-bis(trifluoromethyl)phenyl) and 1o (R = 4-(trifluoromethyl)phenyl) gave the expected products 2p and 2o in the yield of 90 % and 92 %, respectively. It was worth mentioning that bromo- and chloro-substituted cyclic N-sulfonyl ketimines afforded the corresponding products (2k and 2l) in moderate to high yields, which might be employed for further structure modification and might be useful in synthetic chemistry and pharmaceutical chemistry. After realizing the reduction of cyclic N-sulfonyl ketimines possessing five-membered rings, we then turned our attention to a further investigation of the reduction of six-membered cyclic sulfonyl ketimines. As expected, the reduction of the selected cyclic Nsulfonyl ketimines afforded the products (2t, 2u, 2v) with excellent yields up to 99 %.

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Full Paper Table 2. Reduction of various cyclic N-sulfonyl ketimines catalyzed by B(C6F5)3.[a,b]

most likely to affect the reduction. Obviously, the substituents with large steric hindrance could suppress the reduction, for example, in the reduction of 4a and 4b no products were obtained neither at room temperature nor at 110 °C. However, apart from the steric hindrance, the nitrogen atom in the substituents might also influence the reduction, which was confirmed by comparing the reductive results of 1g, 1s, and 4c. In the reduction of 4c, we only isolated the starting material, instead of the sulfonamide. In order to investigate the influence of electro-withdraw substituent, we prepared the cyclic N-sulfonyl ketimine 4d and 4e. But unexpectedly, it gave the complex product with using 4d as the starting material at 25 °C. Then we performed the reduction of 4e both at room temperature and at 110 °C, which provided the starting material instead of the sulfonamide by determination of GC–MS. So the experimental results revealed that the substituents would play an important role in the reduction of cyclic N-sulfonyl ketimines when considering their steric hindrance, electro-withdraw effect, and the nitrogen atoms in the (hetero)aryl substituents.

Figure 2. Unreactive substrates in the reduction.

Comparatively speaking, a gram-scale synthesis is an appropriate way to evaluate the efficiency and practicality of the reductive protocol. When the reduction of 1g was performed under a modified condition in the larger scale experiment, it provided 0.60 g of 2g in a depressed yield (59.5 %) (Scheme 1), due to the fact that the ketimine 1g in the reaction mixture did not converted completely within 24 hours.

Scheme 1. A gram-scale preparation.

[a] Reaction conditions: substrates (0.2 mmol, 1.0 equiv.) and methylphenylsilane (0.22 mmol, 1.1 equiv.) with B(C6F5)3 (5.0 mol %) in toluene (2.0 mL) at 25 °C for 24 h. [b] Isolated yields.

As an exploration of reductive protocol, its feasibility has been tested in a wealth of examples above. In fact, with the further development, the reduction suffered from several limiting factors as well (Figure 2). By comparing the results of reduction in two different substrates, such as 1p and 4a, 1u and 4b, we could identify the steric hindrance of substituent that is Eur. J. Org. Chem. 2019, 6550–6556

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As for the reduction, another significant point to be considered is the selectivity between ketimine and olefin in the cyclic N-sulfonyl ketimine. We prepared two types of ketimines, namely 1e and 5a, to evaluate the selectivity. The results of reductions revealed that the unconjugated C=C in the substituent was highly tolerable under the optimal reaction conditions. It provided 2e as the product when 1e was used as a starting material (Scheme 2). On the contrary, the conjugated C=C in the substituent would be preferred to react when 1.1 equivalent of methylphenylsilane was used as reducing reagent in the reduction of

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Full Paper Inspired by the work of Ishihara in the field of cooperative catalysis, we tried to construct a B(C6F5)3-assisted chiral catalyst with combination of chiral catalyst and B(C6F5)3 in our reduction. We initially examined the inductive effects of the chiral phosphoric acid catalyst 7a, chiral thiourea 7b and 7c (Table 3). The reaction was carried out with using 7a as catalyst at 50 °C resulting in the yield of 40 % with 2 % ee (Table 3, entry 1). Although the reaction proceeded smoothly in the presence of catalyst 7b, it only provided a racemic sulfonamide (Table 3, entry 2). While the chiral thiourea 7c was introduced into the Table 3. Screening of chiral catalysts.[a]

Scheme 2. The selectivity in the reduction of cyclic N-sulfonyl ketimines.

5a. As expected, it could provide the sulfonamide 2q directly when 2.2 equivalent of reducing reagent was used. Based on the Previous reports,[19, 33] we envision that B(C6F5)3 acted as a Lewis acid to catalyze the transformation (Scheme 3). Initially, the Si–H bond was activated by the interaction of methylphenylsilane with electrophilic boron center, which facilitated the attack of the nitrogen atom in cyclic N-sulfonyl ketimine to the silica atom in silane.

Entry

R

Cat.

Yield [%][b]

ee [%][c]

1 2 3 4[d]

CH3 CH3 CH3 C6H5

7a 7b 7c 7c

40 89 40 56

2.0 0 5.5 3

[a] Conditions: substrate (0.2 mmol), B(C6F5)3 (10.0 mol %), chiral catalyst (10.0 mol %), toluene (2.0 mL), 50 °C, 24 h. [b] Isolated yields. [c] ee was determined by chiral HPLC. [d] The reaction was carried out in toluene at 110 °C for 26 h.

Table 4. Optimization of reaction conditions in asymmetric reduction.[a]

Scheme 3. A proposed mechanism of the B(C6F5)3 - catalyzed reduction.

Next, the resulting unstable silylium intermediate 6a and the activated species [HB(C6F5)3]– formed an ion pair in the transition state. Then, the silyliminium/hydridoborate ion pair collapsed to the B(C6F5)3 and 6b, which might be highly unstable on silica gel. In consistent with Piers' report,[16] the desilated sulfonamide was isolated by column chromatography on silica gel. As for other details of the dihydrogen-type activation in FLPs, further explorations and discussions are still underway. Eur. J. Org. Chem. 2019, 6550–6556

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Entry

Temperature (°C)

Solvent

Yield [%][b] Ee [%][c]

1 2 3 3 4 5 6 7 8 9 11 13[d]

50 25 –78 25 25 25 25 25 25 25 25 25

toluene toluene toluene PhCF3 Et2O THF CHCl3 CH2Cl2 DMF PhCl CH3CN toluene/ THF

80 60 N.R. 11 11 11 55 16 N.R. 11 trace 15

5.5 8.4 – 8.3 0 9.4 2.0 3.6 – 6.0 – 9.0

[a] Conditions: 1a (0.2 mmol), B(C6F5)3 (10.0 mol %), 7c (10.0 mol %), toluene (2.0 mL), 34 h. [b] Isolated yields. [c] ee was determined by HPLC. [d] = Solvent: toluene/THF (V:V = 1: 1). DCM = Dichloromethane, Ph-CF3 = Benzotrifluoride, Et2O = Diethyl ether, THF = Tetrahydrofuran, DMF = N,N-Dimethylformamide, PhCl = Chlorobenzene. N.R. = No Reaction.

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Full Paper reduction reaction, the product was obtained in 40 % yield with 5.5 % ee (Table 3, entry 3). To investigate the steric hindrance effect of different substituents, the phenyl-substituted ketimine was used in the reaction. Unfortunately, it afforded the sulfonamide with a poor enantioselectivity as well (Table 3, entry 4). Therefore, these results suggested that the catalyst 7c might show the best asymmetric inducing effect. Next, we tried to examine the effect of various solvents, but only a slightly elevated enantioselectivity (9.0 % ee) and a sharply depressed yield (15 %) was obtained when toluene/THF (V:V = 1:1) were used as the solvent (Table 4, entry 13).

Conclusions In conclusion, we have developed an efficient protocol to reduce the cyclic N-sulfonyl ketimines. The metal-free reduction reaction was catalyzed by the B(C6H5)3 to provide the sulfonamide moieties in good to excellent yields. A series of experiments were also performed to evaluate the practicality and selectivity. Moreover, a plausible mechanism was proposed to illustrate the pathway. With combination of achiral B(C6H5)3 and chiral catalysts, we tried to establish a Lewis acid-assisted Brønsted acid system for asymmetric reduction of cyclic N-sulfonyl ketimines and the preliminary results would be a good foundation for our further research in the enantioselective synthesis.

Experimental Section General Methods and Materials: Commercially available reagent, starting materials and solvents were used without further purification. All reactions were monitored by TLC and visualized by UV lamp (254 nm)/or by staining with a solution of 10 g phosphomolybdic acid and 100 mL of EtOH followed by heating. Flash column chromatography was performed using 200–300 mesh silica gels. HRMS (ESI) was recorded using Agilent 6520 accurate-Mass Q-TOF LC/MS system (1200–6520/Agilent). Low-resolution mass spectra were obtained from GC–MS system (7890A-5975C/Agilent). IR spectra were measured on a Thermo ScientificNicolet IS50 Spectrometer. Ee was determined by HPLC: Agilent Technologies 1260 Infinity II. 1H NMR (400 MHz) and 13C NMR (100 MHz or 150 MHz) spectra were obtained on Bruker 400 M or 600 M nuclear resonance spectrometers. The chemical shifts were given in parts per million (ppm) on the delta (δ) scale. Data for 1H-NMR spectra were reported as follows: chemical shift (ppm, referenced to protium; s = singlet, br s= broad singlet, d = doublet, t = triplet, dd = doublet of doublets, td = triplet of doublets, m = multiplet, coupling constant (Hz), and integration). General Procedure for the Reduction of Cyclic N-Sulfonyl Ketimines: A Schlenk tube equipped with a stir bar was charged with N-sulfonyl ketimines 1 (0.2 mmol, 1equiv.) and B(C6F5)3 (0.01 mmol, 5 mol-%) under nitrogen atmosphere. Then toluene (2 mL) was added via syringe and the resulting mixture was stirred for 5 minutes. The reaction was started by addition of methylphenylsilane and allowed to stir at 25 °C for 24 h. When the reaction was completed, the solvent was evaporated to give a crude product, which was purified with column chromatography on silica gel or prepared TLC. Procedure for the Gram-scale Preparation: A Schlenk flask equipped with a stir bar was charged with N-sulfonyl ketimines 1g (1.0 g, 4.1 mmol, 1.0 equiv.) and B(C6F5)3 (105 mg, 0.2 mmol, Eur. J. Org. Chem. 2019, 6550–6556

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5 mol%) under nitrogen atmosphere. Then toluene (41 mL) was added via syringe and the resulting mixture was stirred for 5 minutes. The reaction was started by addition of methylphenylsilane (551.3 mg, 4.5 mmol, 1.1 equiv.) within 10 minutes and allowed to stir at 25 °C for 24 h. Then the reaction solvent was evaporated to give a crude product, which was purified with column chromatography on silica gel. Procedure for the Enantioselective Reduction of Cyclic N-Sulfonyl Ketimines: A Schlenk tube equipped with a stir bar was charged with chiral catalyst (0.02 mmol, 10 mol%) and B(C6F5)3 (0.02 mmol, 10 mol%) under nitrogen atmosphere. Then toluene (2 mL) was added via syringe and the resulting mixture was stirred for 10 minutes. Next, the ketimines (0.2 mmol, 1 equiv.) were added to the reaction under nitrogen atmosphere. The reaction was started by addition of methylphenylsilane. The reaction was monitored by TLC. The reaction solvent was evaporated to give a crude product, which was purified with column chromatography on silica gel or prepared TLC. 1b, 15 % yield, 9 % ee. HPLC: OD-H column, iPrOH/hexane, 20:80, 0.8 mL/ min, 254 nm. t1 = 14.4 min, t2 = 18.1 min. 3-Methyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2a): White solid, 36.3 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.76 (d, J = 7.8 Hz, 1H), 7.62 (t, J = 7.6 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.39 (d, J = 7.7 Hz, 1H), 5.03 (s, 1H), 4.86–4.69 (m, 1H), 1.61 (d, 3H).13C NMR (150 MHz, CDCl3) δ = 141.8, 135.4, 133.23, 129.2, 123.9, 121.1, 53.4, 21.4. 3-Ethyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2b): White solid, 39.1 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.77 (d, J = 7.7 Hz, 1H), 7.62 (td, J = 7.5 Hz, 1H), 7.52 (t, J = 7.5 Hz, 1H), 7.38 (d, J = 7.8 Hz, 1H), 4.97 (s, 1H), 4.68 (s, 1H), 2.04 (s, 1H), 1.83–1.81 (m, J = 14.8, 7.6 Hz, 1H), 1.02 (t, J = 7.3 Hz, 3H). 13C NMR (100 MHz, CDCl3) 140.2, 135.7, 133.1, 129.2, 124.2, 121.3, 59.0, 28.7, 9.8. 3-Butyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2c): White solid, 44.6 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.72 (d, J = 7.8 Hz, 1H), 7.59 (t, J = 7.1 Hz, 1H), 7.48 (t, J = 7.5 Hz, 1H), 7.36 (d, J = 7.6 Hz, 1H), 5.21 (d, J = 4.7 Hz, 1H), 4.67 (dt, J = 8.7, 4.4 Hz, 1H), 1.98–1.90 (m, 1H), 1.73 (d, J = 9.7 Hz, 1H), 1.43–1.30 (m, 4H), 0.89 (t, J = 7.1 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ = 140.7, 135.5, 133.1, 129.1, 124.2, 121.2, 57.9, 35.5, 27.8, 22.3, 13.9. 3-Hexyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2d): White solid, 50.1 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.75 (d, J = 7.7 Hz, 1H), 7.61 (t, J = 7.5 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.38 (d, J = 7.8 Hz, 1H), 5.00 (s, 1H), 4.78–4.59 (m, 1H), 1.99–1.94 (m, 1H), 1.78–1.72 (m, 1H), 1.47–1.26 (m, 8H), 0.88 (t, J = 6.6 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ = 140.7, 135.6, 133.0, 129.1, 124.1, 121.3, 57.9, 35.8, 31.6, 28.9, 25.7, 22.5, 14.0. MS (EI, m/z): 253.1[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C13H19NSO2) requires m/z 276.1029, found m/z 276.1058. IR: ν 3236, 2973, 2922, 2862, 1652, 1539, 1467, 1399, 1333, 1299, 1278, 1152, 1133, 1075, 1058, 1010, 945, 906, 877, 814, 766, 715, 647, 614. 3-(Pent-4-en-1-yl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2e): White solid, 46.0 mg, 97 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.75 (d, J = 7.7 Hz, 1H), 7.61 (t, J = 7.5 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.37 (d, J = 7.8 Hz, 1H), 5.77 (d, J = 6.8 Hz,1H), 5.10 (s, 1H), 5.06–4.94 (m, 2H), 4.70 (s, 1H), 2.11 (d, J = 7.0 Hz, 2H), 1.98 (s, 1H), 1.76 (d, J = 9.1 Hz, 1H), 1.57 (d, J = 8.8 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ = 140.6, 137.9, 135.6, 133.1, 129.2, 124.2, 121.3, 115.3, 57.8, 35.1, 33.2, 24.8. MS (EI, m/z): 237.0[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C12H15NSO2) requires m/z 260.0716, found m/z 260.0703. IR: 3269, 2951, 2921, 2895, 2852, 1640, 1468, 1452,

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Full Paper 1393, 1319, 1292, 1273, 1244, 1207, 1159, 1142, 1056, 1007, 994, 949, 913, 874, 809, 756, 743, 715, 649, 601.

(100 MHz, CDCl3) δ = 164.2, 161.8, 139.6, 134.7, 133.4, 129.6, 129.5, 125.3, 121.2, 116.3, 116.1, 60.6.

3-Cyclohexyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2f): White solid, 49.7 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.77 (d, J = 7.8 Hz, 1H), 7.62 (t, J = 7.5 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.38 (d, J = 7.8 Hz, 1H), 4.96 (s, 1H), 4.63 (s, 1H), 1.87–1.80 (m, 3H), 1.69–1.67 (m, 2H), 1.34–1.11 (m, 6H). 13C NMR (100 MHz, CDCl3) δ = 138.9, 135.6, 132.9, 129.1, 124.3, 121.3, 77.3, 77.0, 76.7, 62.8, 42.6, 30.6, 26.3, 25.8, 25.7, 25.7. MS (EI, m/z): 251.1[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C13H17NSO2) requires m/z 274.0872, found m/z 274.0857.

3-(3-Fluorophenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2n): White solid, 47.4 mg, 90 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.81 (d, J = 7.3 Hz, 1H), 7.56 (t, J = 5.9 Hz, 2H), 7.40–7.31 (m, 1H), 7.17 (dd, J = 14.4, 7.4 Hz, 2H), 7.12–7.00 (m, 2H), 5.73 (d, J = 4.2 Hz, 1H), 5.41 (s, 1H). 13C NMR (100 MHz, CDCl3) δ = 161.8, 141.4, 139.0, 134.4, 133.5, 130.9, 129.7, 125.3, 123.2, 121.2, 116.1, 114.6, 60.63.

3-Phenyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2g): White solid, 48.6 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.80 (d, J = 7.2 Hz, 1H), 7.62–7.44 (m, 2H), 7.36 (s, 5H), 7.13 (d, J = 7.8 Hz, 1H), 5.71 (s, 1H), 5.17 (s, 1H). 13C NMR (100 MHz, CDCl3) δ = 139.8, 138.7, 134.6, 133.3, 129.4, 129.2, 129.0, 127.5, 125.3, 121.1, 61.3. 3-(4-(tert-Butyl)phenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2h): White solid, 59.7 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.84–7.82 (m, 1H), 7.58–7.53 (m, 2H), 7.41–7.39 (m, 2H), 7.29–7.27 (m, 2H), 7.18–7.16 (m, 1H), 5.70 (d, J = 4.0 Hz, 1H), 4.89 (d, J = 3.6 Hz, 1H), 1.31 (s, 9H). 13C NMR (100 MHz, CDCl3) δ = 152.3, 140.0, 135.5, 135.0, 133.2, 129.4, 127.3, 126.2, 125.4, 121.1, 61.1, 34.6, 31.2. MS (EI, m/z): 301[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C17H19NSO2) requires m/z 324.1029, found m/z 324.1012. IR: 3234, 2968, 2873, 1620, 1446, 1401, 1305, 1268, 1148, 1007, 934, 852, 763, 719, 680. 3-(4-Methoxyphenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2i): White solid, 41.8 mg, 76 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.84v7.82 (m, 1H), 7.58–7.54 (m, 2H), 7.29–7.27 (m, 1H), 7.16– 7.13 (m, 1H), 6.92–6.90 (m, 2H), 5.69 (d, J = 4.0 Hz, 1H), 5.06 (d, J = 4.0 Hz, 1H), 3.82 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 159.5, 143.9, 135.2, 133.2, 129.4, 129.0, 126.5, 121.4, 113.9, 71.9, 55.3. 3-(Naphthalen-2-yl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2j): White solid, 53.1 mg, 90 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.89–7.83 (m, 5H), 7.54–7.53 (m, 4H), 7.36 (d, J = 8.5 Hz, 1H), 7.13 (d, J = 4.9 Hz, 1H), 5.87 (s, 1H), 5.16 (s, 1H). 13C NMR (100 MHz, CDCl3) δ = 139.6, 135.9, 134.8, 133.4, 133.3, 133.1, 129.5, 128.0, 127.8, 127.2, 126.8, 126.8, 125.4, 124.4, 121.2, 61.5. MS (EI, m/z): 295[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C17H13NSO2) requires m/z 318.0559, found m/z 318.0551. 3-(4-Bromophenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2k): White solid, 62.2 mg, 96 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.79 (d, J = 7.7 Hz, 1H), 7.45–7.37 (m, 4H), 7.15 (d, J = 8.5 Hz, 2H), 7.01 (d, J = 6.9 Hz, 1H), 5.69 (d, J = 3.9 Hz, 1H), 5.27–5.26 (m, 1H). 13 C NMR (100 MHz, CDCl3) δ = 139.1, 137.9, 134.5, 133.4, 132.3, 129.6, 129.2, 125.2, 123.0, 121.2, 60.5. MS (EI, m/z): 322[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C13H10NSO2) requires m/z 345.9508, found m/z 345.9510. IR: 3282, 3064, 3040, 1483, 1454, 1389, 1280, 1234, 1191, 1164, 1140, 1068, 1005, 918, 872, 843, 795, 754, 717, 695, 645. 3-(4-Chlorophenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2l): White solid, 52.6 mg, 94 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.83 (d, J = 7.6 Hz, 1H), 7.57–7.55 (m, 2H), 7.37–7.30 (m, 4H), 7.12 (d, J = 6.7 Hz, 1H), 5.71 (d, J = 3.9 Hz, 1H), 5.13 (s, 1H). 13C NMR (100 MHz, CDCl3) δ = 139.2, 137.3, 135.0, 134.6, 133.4, 129.7, 129.4, 128.9, 125.2, 121.2, 60.6. 3-(4-Fluorophenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2m): White solid, 47.4 mg, 90 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.81 (d, J = 7.6 Hz, 1H), 7.59–7.52 (m, 2H), 7.36–7.33 (m, 2H), 7.12–7.04 (m, 3H), 5.72 (d, J = 3.9 Hz, 1H), 5.22 (br, 1H). 13C NMR Eur. J. Org. Chem. 2019, 6550–6556

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3-(4-(Trifluoromethyl)phenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2o): White solid, 57.6 mg, 92 % yield. 1 H NMR (400 MHz, CDCl3) δ = 7.79 (d, J = 8.6 Hz, 1H), 7.62 (d, J = 8.2 Hz, 2H), 7.56–7.51 (m, 4H), 7.13 (d, J = 6.6 Hz, 1H), 5.80 (s, 1H), 5.59 (s, 1H). 13C NMR (100 MHz, CDCl3) δ = 142.9, 138.7, 134.3, 133.5, 131.5, 131.2, 130.9, 130.6, 129.8, 127.8, 126.1, 125.2, 122.4, 121.2, 60.5. MS (EI, m/z): 313[M + ]. HRMS (ES + ) exact mass calculated for [M + Na]+(C14H10F3NSO2) requires m/z 336.0227, found m/z 336.0261. IR: 3265, 2929, 2852, 1618, 1473, 1415, 1393, 1324, 1284, 1234, 1188, 1167, 1130, 1108, 1067, 1014, 917, 876, 852, 797, 754, 739, 712, 645, 618. 3-(3,5-Bis(trifluoromethyl)phenyl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2p): White solid, 68.6 mg, 92 % yield. 1H NMR (400 MHz, [D6]DMSO) δ = 8.88 (s, 1H), 8.24 (s, 2H), 8.11 (s, 1H), 7.92 (d, J = 7.6 Hz, 1H), 7.67 (dt, J = 23.0, 7.4 Hz, 2H), 7.46 (d, J = 7.6 Hz, 1H), 6.22 (s, 1H). 13C NMR (100 MHz, [D6]DMSO) δ = 144.5, 139.1, 135.0, 134.1, 131.4, 131.1, 130.7, 130.5, 128.1, 126.1, 124.9, 122.6, 122.2, 121.3, 58.8. MS (EI, m/z): 381[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C15H9F6NSO2) requires m/z 404.0150, found m/z 404.0105. IR: 3238, 3088, 2798, 1476, 1456, 1404, 1374, 1328, 1290, 1234, 1174, 1125, 1068, 1031, 1005, 925, 906, 848, 814, 778, 761, 729, 706, 703, 681, 652, 633, 600. 3-Phenethyl-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2q): White solid, 42.6 mg, 78 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.76 (d, J = 7.7 Hz, 1H), 7.63–7.55 (m, 1H), 7.53–7.47 (m, 1H), 7.36–7.27 (m, 3H), 7.23–7.18 (m, 3H), 5.07 (q, J = 5.9 Hz, 1H), 4.68 (ddd, J = 9.1, 5.3, 3.6 Hz, 1H), 2.81 (t, J = 7.7 Hz, 2H), 2.32–2.24 (m, 1H), 2.15– 2.03 (m, 1H). 13C NMR (100 MHz, CDCl3) δ = 140.4, 135.6, 133.2, 129.3, 128.7, 128.5, 126.4, 124.2, 121.4, 57.2, 37.5, 32.1. 3-(Benzo[d][1,3]dioxol-5-yl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2r): White solid, 57.2 mg, 99 % yield. 1 H NMR (400 MHz, CDCl3) δ = 7.81 (d, J = 6.9 Hz, 1H), 7.61–7.49 (m, 2H), 7.15 (d, J = 7.2 Hz, 1H), 6.86 (d, J = 8.0 Hz, 1H), 6.81–6.73 (m, 2H), 5.95 (d, J = 2.7 Hz, 2H), 5.64 (d, J = 4.0 Hz, 1H), 5.12 (d, J = 3.7 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ = 148.6, 148.4, 139.8, 134.9, 133.3, 132.3, 129.6, 125.3, 121.6, 121.2, 108.5, 107.6, 101.5, 77.3, 77.0, 76.7, 61.2. MS (EI, m/z): 289[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C14H11NSO4) requires m/z 312.0301, found m/z 312.0280. IR: 3220, 3001, 2915, 2789, 1498, 1478, 1396, 1379, 1314, 1293, 1256, 1186, 1152, 1127, 1110, 1059, 1037, 930, 868, 821, 765, 741, 709, 692, 645, 623. 3-(Thiophen-2-yl)-2,3-dihydrobenzo[d]isothiazole 1,1-Dioxide (2s): White solid, 37.7 mg, 75 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.83 (d, J = 7.1 Hz, 1H), 7.66–7.54 (m, 2H), 7.36–7.29 (m, 2H), 7.16 (d, J = 3.2 Hz, 1H), 7.05–6.99 (m, 1H), 6.03 (s, 1H), 5.04 (s, 1H). 13C NMR (100 MHz, CDCl3) δ = 141.4, 139.2, 135.0, 133.38, 129.9, 127.2, 126.9, 125.4, 121.2, 56.5. MS (EI, m/z): 251[M+]. HRMS (ES+) exact mass calculated for [M + H]+(C11H10NS2O2) requires m/z 252.01475, found m/z 252.01486. IR: 3256, 2975, 2854, 1567, 1493, 1418, 1317, 1305, 1166, 1129, 913, 857, 799, 773, 743, 725, 663. 3,4-Dihydrobenzo[e][1,2,3]oxathiazine 2,2-Dioxide (2t): White solid, 36.7 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.30 (t, J =

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Full Paper 7.7 Hz, 1H), 7.15 (dt, J = 15.5, 7.5 Hz, 2H), 6.96 (d, J = 8.3 Hz, 1H), 4.91 (s, 1H), 4.63 (d, J = 7.9 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ = 151.6, 129.3, 126.5, 125.2, 118.6, 118.2, 46.4. 4-Methyl-3,4-dihydrobenzo[e][1,2,3]oxathiazine 2,2-Dioxide (2u): White solid, 39.4 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.29 (t, J = 7.0 Hz, 1H), 7.19 (d, J = 6.0 Hz, 2H), 6.95 (d, J = 8.2 Hz, 1H), 4.87 (d, J = 7.1 Hz, 1H), 4.76 (s, 1H), 1.69 (d, J = 6.7 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ = 150.9, 129.4, 126.3, 125.4, 123.6, 118.7, 52.9, 20.1. 6-Fluoro-3,4-dihydrobenzo[e][1,2,3]oxathiazine 2,2-Dioxide (2v): White solid, 40.2 mg, 99 % yield. 1H NMR (400 MHz, CDCl3) δ = 7.07–6.97 (m, 2H), 6.86 (dd, J = 8.0, 2.6 Hz, 1H), 4.77 (s, 1H), 4.65 (s, 2H). 13C NMR (100 MHz, CDCl3) δ = 160.4, 157.9, 147.4, 120.2, 119.5, 116.4, 116.1, 113.1, 112.9, 46.2. MS (EI, m/z): 203[M+]. HRMS (ES+) exact mass calculated for [M + Na]+(C7H6FNSO3) requires m/z 225.9945, found m/z 225.9990. IR: 3266, 3130, 2973, 2870, 1635, 1488, 1450, 1435, 1374, 1288, 1249, 1205, 1169, 1145, 1099, 1048, 1012, 945, 855, 809, 775, 752, 710, 660, 618.

Acknowledgments We are grateful for the financial support from the National Natural Science Foundation of China (Grant No.21871067), the Natural Science Foundation of Guangdong Province (Grant No. 2018A030313038), Shenzhen Fundamental Research Projects (Grant No. JCYJ20180306171838187), and Harbin Institute of Technology (Shenzhen) (Talent Development Starting Fund from Shenzhen Government). We also acknowledge Prof. Dr. Feng Cao (School of Science, Harbin Institute of Technology, Shenzhen) for the IR spectra analysis. Keywords: Cyclic sulfonamide · B(C6F5)3 · Metal-free · Reduction · Cooperative catalysis [1] G. C. Welch, R. R. S. Juan, J. D. Masuda, D. W. Stephan, Science 2006, 314, 1124–1126. [2] a) M. Khandelwal, R. J. Wehmschulte, Angew. Chem. Int. Ed. 2012, 51, 7323–7326; Angew. Chem. 2012, 124, 7435–7439; b) S. N. Riduan, Y. Zhang, J. Y. Ying, Angew. Chem. Int. Ed. 2009, 48, 3322–3325; Angew. Chem. 2009, 121, 3372–3375; c) C. D.Das Neves Gomes, O. Jacquet, C. Villiers, P. Thuery, M. Ephritikhine, T. Cantat, Angew. Chem. Int. Ed. 2012, 51, 187–190; Angew. Chem. 2012, 124, 191–194; d) C. D. Gomes, E. Blondiaux, P. Thuery, T. Cantat, Chem. Eur. J. 2014, 20, 7098; e) E. Blondiaux, T. Cantat, Chem. Commun. 2014, 50, 9349–9352; f) J.-M. Yang, Z.-Q. Li, S.-F. Zhu, Chin. J. Org. Chem. 2017, 37, 2481–2497; g) D. W. Stephen, J. Am. Chem. Soc. 2015, 137, 10018–10032. [3] E. J. Corey, Angew. Chem. Int. Ed. 2009, 48, 2100–2117; Angew. Chem. 2009, 121, 2134–2151. [4] S. J. Geier, P. A. Chase, D. W. Stephan, Chem. Commun. 2010, 46, 4884– 4886. [5] Z. Zhang, H. Du, Angew. Chem. Int. Ed. 2015, 54, 623–626; Angew. Chem. 2015, 127, 633–636. [6] Y. Liu, H. Du, J. Am. Chem. Soc. 2013, 135, 12968–2971. [7] Z. Zhang, H. Du, Org. Lett. 2015, 17, 2816–2819. [8] Z. Zhang, H. Du, Org. Lett. 2015, 17, 6266–6269. [9] S. J. Geier, D. W. Stephen, J. Am. Chem. Soc. 2009, 131, 3476–3477. [10] G. Eros, H. Mehdi, I. Pápaie, T. A. Rokob, P. Király, G. Tárkányi, T. Soós, Angew. Chem. Int. Ed. 2010, 49, 6559–6563; Angew. Chem. 2010, 122, 6709–6713.

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