TMDS system

Tetrahedron 68 (2012) 3151e3155

Contents lists available at SciVerse ScienceDirect

Tetrahedron journal homepage: www.elsevier.com/locate/tet

Reduction of phosphine oxides to phosphines with the InBr3/TMDS system
tay a, Dominique Delbrayelle b, Ge
rard Mignani c, Marc Lemaire a, * Leyla Pehlivan a, Estelle Me Laboratoire de Catalyse et Synth ese Organique, Institut de Chimie et Biochimie Moleculaires et Supramoleculaires (ICBMS), CNRS, UMR5246, Universit
e Lyon 1, 43 Boulevard du 11 Novembre 1918, Bat CPE, 69622 Villeurbanne, France b Minakem SAS, 145 Chemin des Lilas, 59310 Beuvry la Foret, France c Rhodia, Lyon Research center, 85, Avenue des Freres Perret, BP 62, 69192 Saint-Fons Cedex, France a

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 November 2011 Received in revised form 14 February 2012 Accepted 26 February 2012 Available online 3 March 2012

An efficient method for the reduction of phosphine oxide derivatives into their corresponding phosphines is described. The system InBr3/TMDS allows the reduction of different secondary and tertiary phosphine oxides as well as aliphatic and aromatic phosphine oxides. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Reduction Phosphine oxide TMDS InBr3 Phosphine

1. Introduction Tertiary and secondary phosphines are important compounds in organic synthesis. They are widely used for metal ligation since many transition metal complexes contain phosphines and diphosphines as ligands.1 These ones used as catalysts allow hydrogenation, hydroformylation, hydrocyanation, allylic substitution, hydrosilylations or palladium-catalyzed coupling reactions. Phosphines such as triphenylphosphine (TPP), for example, are also used in various types of reactions: Wittig,2 Mitsunobu,3 Appel,4 Staudinger5 reactions etc. Triphenylphosphine oxide (TPPO) is generated as a by-product in these reactions and is considered as a waste even if some progress was made for a catalytic version of these reactions.6 Thus, finding an appropriate method to convert phosphine oxides derivatives into their corresponding phosphines appears to be a good solution. Indeed the initial phosphine could be regenerated and reused. Reduction of triphenylphosphine oxide has been performed under different conditions. Aluminum hydrides7 can be employed for this transformation but they are not appropriate for the industry: they are expensive, highly reactive with air and water, difficult to handle. Other systems have been developed for the direct reduction of TPPO. SmI2/HMPA,8 TiCp2Cl2/Mg,9 Bi/TiO2,10 hydrocarbon

* Corresponding Lemaire).

author.

E-mail

address:

[email protected]

0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2012.02.063

(M.

associated with activated carbon at 350
C,11 SiCl4 with a metal12 and sulfur derivatives13 can be cited. Another way to prepare phosphines is the electroreduction of triphenylphosphine oxides.14,15 The indirect reduction of TPPO to TPP via the corresponding triphenylphosphine dichloride has also been described. It includes a step with a chlorination agent. Then phosgene,16 oxalyl chloride associated with PbBr2 or other additives17 were used and the dichloride derivative requires to be reduced with a metal as sodium or aluminum. From a cost and/or safety point of view these cited methods are not recommended. Finally, silanes such as Ph2SiH,6 HSiCl3,18 (EtO)3SiH/Ti(OiPr)419 have been used and give the expected phosphines with good yields, but unfortunately several silanes have been demonstrated harmful since they generate a dangerous, pyrophoric and toxic SiH420 gas. As a consequence, more stable hydrosiloxanes (SieOeSi) are considered as being highly interesting as the ultimate waste is silica. Among these derivatives, PMHS (Polymethylhydrosiloxane), a 40-unit polymeric chain, was efficiently used with 1 equiv of Ti(OiPr)4 by Lawrence to give phosphines.19 TMDS (1,1,3,3-tetramethyldisiloxane) (Scheme 1) also constitutes a safe siloxane, which derives from a by-product of the industry and can be recycled for the water-repellent treatment of materials.

Scheme 1. TMDS structure.

3152

L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155

In that way our group previously described the reduction of tertiary and secondary phosphine oxides with the system Ti(OiPr)4/ TMDS (Scheme 2).21

Scheme 2.

A mechanistic insight has revealed the presence of silicon radical species. Moreover, Sakai22 recently described the reduction of different functions in the presence of catalytic amount of InBr3 and silane. In these papers they propose the formation of radical species. As a consequence, it was interesting to study the reduction of phosphine oxide with the association of TMDS/Indium.

Table 2 Comparison with previous conditions of reduction

2. Results and discussion Herein, we describe the efficient reduction of phosphine oxide derivatives by the catalytic system InBr3/TMDS. We started our investigation by testing different sources of indium with PMHS or TMDS as hydride sources. Triphenylphosphine oxide was considered as the model substrate. All tests were performed with 1 mol % of indium III catalyst (Table 1). At 100
C with TMDS and indium triflate, the reduction of TPPO occurred with a conversion of 28% (Table 1, entry 1). Under the same conditions InBr3 gave a complete conversion into the desired TPP (Table 1, entry 2). In order to see the temperature effect on this reaction, the temperature was decreased to 60
C. We then observed a slight conversion of 10% after 18 h and after 3 days the reaction was still not complete (Table 1, entry 3). A test with PMHS (40 unit polymeric chain) under the optimal conditions allowed us to eliminate the PMHS as a potential reducing agent for this reduction since no TPP was obtained (Table 1, entry 4). This observation could be in agreement with the formation of a silyl radical species. Indeed the accessibility of the formed radical on a polymeric structure is limited. Other sources of indium such as indium acetate (Table 1, entry 5) or indium acetylacetonate (Table 1, entry 6) did not allow the conversion of TPPO into the attempted TPP. One more experiment was run to reduce triphenylphosphine oxide with 5 mol % of copper triflate instead of indium complexes. Only 80% conversion was reached in 23 h. This lower reactivity was confirmed again with the reduction of tributylphosphine oxide. After 20 h only 28% conversion was observed. Table 1 Reduction of TPPO with different sources of indium

Entry 1 2 3 4 5 6

Indium In(OTf)3 InBr3 InBr3 InBr3 In(OAc)3 In(acac)3

reduction of TPPO was tested in methylcyclohexane (MCH) (Table 2). In toluene at 100
C, the reaction was complete (Table 2, entry 1). However in MCH at 60
C the TPP was not obtained and only the initial TPPO was observed (Table 2, entry 2). During the previous study realized on the Ti/TMDS system, the formation of water during the reaction was supposed because the addition of dehydrating agent like sodium sulfate allowed a better conversion. This was in agreement with the proposed mechanism. Thus, the addition of Na2SO4 was considered but did not improve the reduction since the starting material remained intact (Table 2, entry 3). On the opposite of the titanium cluster it is known that InBr3 is more stable. When temperature was increased to 100
C and without the presence of a desiccant, the formation of the desired product was observed with a conversion of 79% (Table 2, entry 4). This result is however less interesting than the reduction in toluene. Reaction performed without solvent did not allow the formation of the phosphine (Table 2, entry 5).

SieH TMDS TMDS TMDS PMHS TMDS TMDS

Temperature


100 C 100
C 60
C 100
C 100
C 100
C

Conv.a (%) 28% >99% 10% (50%)b 0 <5% 0

a Conversions were determined by 31P NMR after 18 h except for entry 2 only 7 h were needed. b After 3 days.

Based on these results InBr3 was kept as catalyst with TMDS as hydride source. In order to compare these results with those obtained previously with the system Ti(OiPr)4/TMDS/Na2SO4,

Entry 1 2 3 4 5 a

Solvent Toluene MCH MCH MCH d

T (
C)

SieH (equiv) 3 2.5 3 3 3




(1.5) (1.25) (1.5) (1.5) (1.5)

Conversions were determined by

100 C 60
C 60
C 100
C 100
C 31

Desiccant

Conv.a (%)

ee ee Na2SO4 (10%) ee ee

>99% 0 0 79% 0

P NMR after 18 h.

When decreasing the SieH quantity (1 mol/mol of substrate) in 18 h the conversion reached only 90% whereas with 1.5 mol/mol the conversion was complete in 7 h. Best conditions (Table 2, entry 1) were then applied on different phosphine oxide derivatives. The scope and limitation of the system was then explored. Triphenylphosphine oxide was efficiently reduced after 7 h of reaction into the corresponding triphenylphosphine (Table 3, entry 1). The methyldiphenylphosphine oxide was also reduced completely and gave after 18 h the corresponding phosphine. However this phosphine is readily re-oxidized during the work-up, therefore it was necessary to protect it into phosphine borane. The corresponding phosphine borane was isolated with a quantitative yield (Table 3, entry 2). The system InBr3/TMDS allows the reduction of phosphine oxide derivatives, which contain a methoxy group since the substrate 1c was totally converted into 2c and isolated with a quantitative yield as the borane phosphine (Table 3, entry 3). However if the substrate contains a double bond, this one is also reduced. Indeed for the reduction of compound 1d both phosphine oxide and double bond were reduced to give the phosphine 2d. Although it was reduced with 98% conversion, 2d was isolated with only 21% yield (Table 3, entry 4). Indeed this product, even after protection, was not stable and was quickly re-oxidized. In order to check the selectivity between phosphine oxide the CeC double bond, reaction was performed with 1 mol/mol of substrate. After 18 h, the formation of 33% of the reduced phosphine oxide was noticed by NMR (keeping the double bond). However at higher conversions the CeC double bond was reduced. Same observation concerning the double bond was noticed on the 3-methyl-1-phenyl-2-phospholene oxide 1e since after 40 h both oxide and double bond were reduced. 2e was isolated with 95% yield (Table 3, entry 5). Concerning mechanistic consideration the formation of a radical species with the indium system seems correct as soon as the double bonds are reduced at the same time

L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155

3153

Table 3 Application on different phosphine oxides Entry

Substrates

Products

Reaction time (h)

Conv. (%)a

Isolated yield (%)b

1

1a

2a

7

>99%

84%

2

1b

2b

18

>99%

>99%

3

1c

2c

18

>99%

>99%

4

1d

2d

18

>98%

21%c

5

1e

2e

40

>95%

95%d

6

1f

2f

22

72%e

55%

7

1g

2g

22

>99%

8

1h

2h

24

0%

ee

9

1i

2i

30

>95%

>99%

10

1j

2j

18

86%

80%

11

1k

2k

18

>99%

96%

12

1l

2l

18

>92%

70%

13

1m

2m

17

>99%

ND

f

80%

Conditions: Substrate (5 mmol), InBr3 (1 mol %), TMDS (1.5 equiv), Toluene (1 M), 100
C. a Conversions were determined by 31P NMR. b Yield after flash chromatography. c Reoxidation of the phospshine was observed. d After 18 h phosphine oxide was completely reduced and the double bond was partially reduced. e Reaction required 10 mol % of InBr3. f 2 mol % of InBr3 and 3 equiv of TMDS were used.

and no products come from hydrosilylation were observed. The radical-based hydrosilylation of carbonecarbon double bonds was already described with silane.23 The reduction of cyclohexyldiphenylphosphine oxide 1f was particular since it required 10 mol % of InBr3. When 1 mol % of catalyst was used no reaction

occurred and only the starting material was detected. After 22 h and a conversion of 72%, product 2f was isolated with 55% (Table 3, entry 6). Conditions of reaction were then applied on dppp(O) 1g and the corresponding dppp 2g was obtained with a total conversion and isolated with 80% (Table 3, entry 7). It is interesting to

3154

L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155

notice that no conversion was observed on dppb(O) 1h. Indeed dppb(O) is not soluble in toluene and in this way it prevents the reaction to occur (Table 3, entry 8). In MCH the same problem of solubility was noticed and no conversion was observed. The reduction was then tested on aliphatic phosphine oxides. A first conclusive test on tricyclohexylphosphine 1i allowed us to conclude that both aromatic and aliphatic phosphine oxides could be reduced. Then 2i was isolated with 95% yield after a conversion of 95% (Table 3, entry 9). Tri-n-butylphosphine oxide 1j was converted into 2j with 86% conversion and isolated with a good yield of 80% (Table 3, entry 10). With a longer alkyl chain (C8), the conversion was total and 1k was isolated with 96% yield to give the protected phosphine borane 2k (Table 3, entry 11).The reduction of secondary phosphine oxides was also considered. Conditions were applied on diphenylphosphine oxide 1l and after 18 h 92% of 1l was converted. The diphenylphosphine was then protected and isolated with 70% yield (Table 3, entry 12). As for compound 2d, the protective step is delicate since the reoxidation is fast. Finally, the reaction can also be applied for the reduction of phosphinic acids. An example on diphenylphosphinic acid 1m was done and was successfully converted into 2m (Table 3, entry 13). From all data in Table 3, the system TMDS/InBr3 can be compared to the results obtained with TMDS/Ti(OiPr)4. More precisely, secondary, tertiary phosphine oxide and diphosphine oxide can be reduced. The only noticed difference was the difficulty to reduce the diphenylphosphinobutane oxide, which is not soluble in the reaction media. Several experiments were also made for the reduction of BINAP oxide but no reaction occurred, probably because of the low solubility of BINAP oxide in toluene and in most of low polar organic solvents. However, even if double bonds are also reduced, concerning mechanistic consideration the formation of a radical species with the indium system could be considered. The mechanism will be further studied. 3. Conclusion In conclusion we have developed an efficient method to reduce phosphine oxides into their corresponding phosphines. The system InBr3/TMDS has proven to be efficient to reduce aromatic and aliphatic phosphine oxides, to reduce tertiary and secondary phosphine oxides and finally to reduce phosphinic acids. This new methodology can constitute an alternative to the current methods to reduce phosphine oxides or recycle phosphine engaged in organic reactions. 4. Experimental part

argon atmosphere. The reaction mixture was stirred at 100
C during 7e40 h depending on the substrate (the reaction was monitored by 31P NMR). After complete consumption of the reagent the mixture was kept under argon in the sealed tube and cooled to 0
C. A solution of BH3.SMe2 (2 M in THF, 1 equiv) was then slowly added. After 1 h at room temperature, 31P NMR analysis of an aliquot indicates complete conversion to phosphine borane adduct. The crude was poured in an erlenmeyer flask and silica gel was carefully added while stirring. When silica gel was added in the reaction mixture, a slightly exothermic reaction was observed. The reaction mixture was then filtered on silica gel and washed several times with ethyl acetate. After evaporation of the ethyl acetate, the residue was purified by flash chromatography on silica gel with pure cyclohexane to afford the desired phosphineeborane. Compounds 2a, 2g, 2h are purified without the BH3 protection. 4.2.1. Triphenylphosphine [603e35-0] 2a. White solid. 1H NMR (300 MHz, CDCl3): d¼7.30e7.36 (m, 15H). 13C NMR (75 MHz, CDCl3): d¼137.5 (s, JCP¼10.5 Hz), 134.1 (d, JCP¼19.1 Hz), 128.9 (d, JCP¼19.1 Hz), 128.8 (s). 31P NMR (121 MHz, CDCl3): d¼-4.3. 4.2.2. Methyldiphenylphosphine-borane [54067-17-3] 2b. Colorless oil. 1H NMR (300 MHz, CDCl3): d¼7.51e7.58 (m, 4H), 7.26e7.34 (m, 6H), 1.72 (d, J¼10.2 Hz, 3H). 13C NMR (75 MHz, CDCl3): d¼131.9 (d, JCP¼9.2 Hz), 131.3, 130.2, 129.0 (d, JCP¼9.8 Hz), and 12.0 (d, JCP¼40 Hz). 31P NMR (121 MHz, CDCl3): d¼11.2. 4.2.3. Diphenyl(methoxymethyl)phosphineeborane 2c. White oil. 1H NMR (300 MHz, CDCl3): d¼7.73e7.80 (m, 4H), 7.42e7.54 (m, 6H), 4.27 (s, 2H), 3.42 (s, 3H). 13C NMR (75 MHz, CDCl3): d¼133.3 (d, JCP¼9.2 Hz), 131.7 (d, JCP¼2.5 Hz), 129.0 (d, JCP¼10.5 Hz), 127.8 (d, JCP¼55.9 Hz), 70.4 (d, JCP¼43.8 Hz), 62.1 (d, JCP¼8.6 Hz). 31P NMR (121 MHz, CDCl3): d¼16.5. 4.2.4. n-Propyldiphenylphosphine-borane [1013636-31-1] 2d. White viscous oil. 1H NMR (300 MHz, CDCl3): d¼7.65e7.72 (m, 4H), 7.40e7.51 (m, 6H), 2.15e2.24 (m, 2H), 1.46e1.62 (m, 2H), 1.01 (t, J¼7.1 Hz, 3H). 13C NMR (75 MHz, CDCl3): d¼132.4 (d, JCP¼8.6 Hz), 131.3 (d, JCP¼2.5 Hz), 130.3, 129.1 (d, JCP¼9.9 Hz), 28.0 (d, JCP¼36.4 Hz), 17.0, and 16.1 (d, JCP¼14.5 Hz). 31P NMR (121 MHz, CDCl3): d¼16.9. 4.2.5. 3-Methyl-1-phenylphospholane-borane [313478e78-3] 2e. Colorless oil. 1H NMR (300 MHz, CDCl3): d¼7.64e7.71 (m, 2H), 7.39e7.41 (m, 3H), 1.92e2.30 (m, 5H), 1.50e1.64 (m, 2H), 1.13 (t, J¼6.6 Hz, 3H). 13C NMR (75 MHz, CDCl3): d¼131.5 (d, JCP¼9.2 Hz), 131.3 (d, JCP¼2.5 Hz), 129.1 (d, JCP¼9.2 Hz), 38.7, 36.6, 28.4 (d, JCP¼36.4 Hz), 27.2, and 21.4. 31P NMR (121 MHz, CDCl3): d¼31.6.

4.1. General All reagents were obtained commercially. Tetramethyldisiloxane, 97% (TMDS) was purchased from Aldrich, anhydrous Toluene from Acros, indium bromide (III), 99.999% from Aldrich and the phosphine oxide derivatives from Aldrich and Alfa Aesar. All reagents and reactants were used without further purification. All reactions were performed under an inert atmosphere (argon) in a sealed tube. 1H NMR, 13C NMR and proton coupled 31P NMR spectra were recorded on a BRUKER DRX 300 or BRUKER ALS 300 and measurements are given in parts per million. Chemical shifts are given in ppm.

4.2.6. Diphenylcyclohexylphosphine borane [127686-90-2] 2f. White solid. 1H NMR (300 MHz, CDCl3): d¼7.70e7.77 (m, 4H), 7.41e7.48 (m, 6H), 2.33e2.46 (m, 1H), 1.56e1.85 (m, 5H), 1.40e1.53 (m, 2H), 1.23e1.30 (m, 3H). 13C NMR (75 MHz, CDCl3): d¼132.9 (d, JCP¼8.6 Hz), 131.2 (d, JCP¼2.4 Hz), 128.9 (d, JCP¼9.9 Hz), 33.9 (d, JCP¼35.8 Hz), 26.0e30.0 (m, Cy). 31P NMR (121 MHz, CDCl3): d¼22.3.

4.2. General procedure for the preparation of compounds 2b to 2f and 2i to 2l

4.2.7. 1,3-Bis(diphenylphosphino)propane [6737-42-4] 2g. White viscous oil. 1H NMR (300 MHz, CDCl3): d¼7.34e7.40 (m, 8H), 7.26e7.28 (m, 12H), 2.20 (m, t, J¼7.7 Hz, 4H), 1.57e1.68 (m, 2H). 13C NMR (75 MHz, CDCl3): d¼138.8 (d, JCP¼12.9 Hz), 132.9 (d, JCP¼18.5 Hz), 128.7 (d, JCP¼11.7 Hz), 128.67, 29.8 (t, JCP¼12.3 Hz), and 27.2. 31P NMR (121 MHz, CDCl3): d¼-16.2.

In a sealed tube containing a solution of the phosphine oxide derivative (5 mmol) in anhydrous toluene (1 M) was added InBr3 (1 mol %, 0.05 mmol) and the TMDS (1.5 equiv, 7.5 mmol) under an

4.2.8. Tricyclohexylphosphineeborane [101965-91-7] 2i. White solid. 1H NMR (300 MHz, CDCl3): d¼1.71e1.84 (m, 18H), 1.23e1.41 (m, 15H). 13C NMR (75 MHz, CDCl3): d¼31.2 (d, JCP¼30.2 Hz), 28.2 (d,

L. Pehlivan et al. / Tetrahedron 68 (2012) 3151e3155

JCP¼1.8 Hz), 27.6 (d, JCP¼10.5 Hz) and 26.5. CDCl3): d¼29.3.

31

P NMR (121 MHz,

4.2.9. Tri-n-butylphosphine-borane [4259-20-5] 2j. Colorless oil. 1H NMR (300 MHz, CDCl3): d¼1.38e1.58 (m, 18H), 0.93 (t, J¼7.2 Hz, 9H). 13C NMR (75 MHz, CDCl3): d¼24.6 (d, JCP¼2.5 Hz), 24.2 (d, JCP¼12.3 Hz), 22.8 (d, JCP¼34.5 Hz), and 13.5 (s). 31P NMR (121 MHz, CDCl3): d¼15.6. 4.2.10. Tri-n-octylphosphine-borane [101965-92-8] 2k. Colorless oil. H NMR (300 MHz, CDCl3): d¼1.39e1.54 (m, 12H), 1.21e1.37 (m, 30H), 0.85 (t, J¼6.8 Hz, 9H). 13C NMR (75 MHz, CDCl3): d¼32.0, 29.3 (d, JCP¼3.7 Hz), 22.8 and 14.3. 31P NMR (121 MHz, CDCl3): d¼15.6. 1

4.2.11. Diphenylphosphine-borane [41593-58-2] 2l. White solid. 1H NMR (300 MHz, CDCl3): d¼7.50e7.57 (m, 4H), 7.27e7.37 (m, 6H). 13 C NMR (75 MHz, CDCl3): d¼133.1 (d, JCP¼9.2 Hz), 131.8 (d, JCP¼2.5 Hz), 129.2 (d, JCP¼10.5 Hz), and 126.3 (d, JCP¼56.7 Hz). 31P NMR (121 MHz, CDCl3): d¼2.2 (d). Acknowledgements
riel This work was supported by the Fond Unique Interministe ‘REDSUP’. Supplementary data Supplementary data related to this article can be found online at doi:10.1016/j.tet.2012.02.063. References and notes 1. (a) Comprehensive Asymmetric Catalysis IeIII; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin, 1999; (b) Buchwald, S. L.; Mauger, C.; Mignani, G.; Scholz, U. Adv. Synth. Catal. 2006, 348, 23e39; (c) Berthod, M.; Mignani, G.; Woodward, G.; Lemaire, M. Chem. Rev. 2005, 105, 1801e1836. 2. (a) Wittig, G.; Geissler, G. Liebigs Ann. 1953, 580, 44e57; (b) Maryanoff, B. E.; Reitz, A. B. Chem. Rev. 1988, 89, 863e927. 3. (a) Mitsunobu, O.; Yamada, M.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1967, 40, 935e939; (b) But, T. Y. S.; Toy, P. H. Chem. Asian J. 2007, 2, 1340e1355.

3155

4. Appel, R. Angew. Chem. 1975, 87, 863e874; Green. Chem. 1975, 14, 801e811; Buchanan, J. G.; Sable, H. Z. In; Thyagarajan, B. S., Ed. Selective Organic Transformations; Wiley-Interscience: New York, 1972; vol. 2, pp 1e95. 5. Staudinger, H.; Meyer, J. Helv. Chim. Acta 1919, 2, 635e646. 6. Van Kalkeren, H. A.; Leenders, S. H. A. M.; Hommersom, C. R. A.; Rutjes, F. P. J. T.; Van Delft, F. L. Chem.dEur. J. 2011, 17, 11290e11295. 7. (a) Imamoto, T.; Takeyama, T.; Kusumoto, T. Chem. Lett. 1985, 1491e1492; (b) Busacca, C. A.; Raju, R.; Grinberg, N.; Haddad, N.; James-Jones, P.; Lee, H.; Lorenz, J. C.; Saha, A.; Senanayake, C. H. J. Org. Chem. 2008, 73, 1524e1531; (c) Malpass, D. B.; Yeargin, G. S. U.S. patent 4,133,783, 1978; Bootle-Wilbraham, A.; Head, S.; Longstaff, J.; Wyatt, P. Tetrahedron Lett. 1999, 40, 5267e5270; (d) Cernia, E.; Giongo, G. M.; Marcati, F.; Marconi, W.; Palladino, N. Inorg. Chim. Acta 1974, 11, 195e200; (e) Griffin, S.; Heath, L.; Wyatt, P. Tetrahedron Lett. 1998, 39, 4405e4406. 8. Handa, Y.; Inanaga, J.; Yamaguchi, M. J. Chem. Soc., Chem. Commun. 1989, 298e299. 9. Mathey, F.; Maillet, R. Tetrahedron Lett. 1980, 21, 2525e2526. 10. Hagemeyer, A.; Rieker, C. W.; Lautensack, T.; Hermeling, D. U.S. 5,689,005A, 1997. 11. Dockner, T. U.S. 4,727,193 A, 1988. 12. Fritzsche, H.; Hasserodt, U.; Van Olmen, J. U.S. 3,280,195, 1966. 13. (a) Petersson, M. J.; Loughlin, W. A.; Jenkins, I. D. Chem. Commun. 2008, 4493e4494; (b) Townsend, J. M.; Valentine, D. H. U.S. 4,008,282B, 1977. 14. Tanaka, H.; Yano, T.; Kobayashi, K.; Kamenoue, S.; Kuroboshi, M.; Kawakubo, H. Synlett 2011, 582e584. 15. Griesbach, U.; Weiskopf, V.; Maase, M.; WO 2005/031040, 2005. 16. Hermeling, D.; Randolf, H.; Peter, L.; Gerhard, R.; Hardo, S. DE 19532310 A1, 1997. 17. (a) Tanaka, H.; Kuroboshi, M.; Yano, T.; Hoshino, M.; Kawakubo, H. EP2278048, 2009; (b) Yano, T.; Hoshino, M.; Kuroboshi, M.; Tanaka, H. Synlett 2010, 801e803. 18. (a) Segall, Y.; Granoth, I.; Kalir, A. J. Chem. Soc., Chem. Commun. 1974, 501e502; (b) Davis, W. R.; Gordon, M D. U.S. 4,131,624, 1978. 19. Coumbe, T.; Lawrence, N. J.; Muhammad, F. Tetrahedron Lett. 1994, 35, 625e628. 20. Berk, S. C.; Buchwald, S. L. J. Org. Chem. 1993, 58, 3221.
guillon, A.; Mohamad, J.; Mignani, G.; Docherty, G.; 21. (a) Berthod, M.; Favre-Re
guillon, A.; Mignani, Lemaire, M. Synlett 2007, 1545e1548; (b) Petit, C.; Favre-Re
guillon, G.; Lemaire, M. Green. Chem. 2010, 12, 326e330; (c) Petit, C.; Favre-Re A.; Albela, B.; Bonneviot, L.; Mignani, G.; Lemaire, M. Organometallics 2009, 28, 6379e6382. 22. (a) Sakai, N.; Moriya, T.; Konakahara, T. J. Org. Chem. 2007, 72, 5920e5922; (b) Sakai, N.; Fujii, K.; Konakahara, T. Tetrahedron Lett. 2008, 49, 6873e6875; (c) Sakai, N.; Moriya, T.; Fujii, K.; Konakahara, T. Synthesis 2008, 3533e3536; (d) Sakai, N.; Moritaka, K.; Konakahara, T. Eur. J. Org. Chem. 2009, 4123e4127; (e) Sakai, N.; Kawana, K.; Ikeda, R.; Nakaike, Y.; Konakahara, T. Eur. J. Org. Chem. 2011, 3178e3183; (f) Sakai, N.; Nagasawa, K.; Ikeda, R.; Nakaike, Y.; Konakahara, T. Tetrahedron Lett. 2011, 52, 3133e3136; (g) Sakai, N.; Usui, Y.; Ikeda, R.; Konakahara, T. Adv. Synth. Catal. 2011, 353, 3397e3401.
e, J. Molecules 2012, 17, 527e550. 23. Chatgilialoglua, C.; Laleve