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THE SYNTHESIS OF R(+) or S(-) α-NAPHTHYLPHENYLMETHYLSILANE
516
THE SYNTHESIS OF R( + ) or S(-) oc-NAPHTHYLPHENYLMETHYLSILANE ROBERT J.P. CORRIU and JOEL J.E. MOREAU Institut de Chimie Fine - Universite des Sciences et Techniques du Languedoc 34060 Montpellier-cedex
L1AIH4 oc-NpPhSi(OMe) 2
MeVOH MeANHMe oc-NpPhSiH2
oc-NpPhSiH2
Et20
> (PPh3)3RhCl benzene
Ph I
Ph I + oc-Np - S i - H + H 2 I 0(-)Eph
I
1) MeMgBr 2) H 3 0 +
II
Ph
crystallization ->
oc-NpPhMeSi H
[
oc-Np - Si - Me
[«to + 34.5°
optical purity 96# yield W%
INTRODUCTION Stereochemistry at silicon has been widely studied over the past years. *■ The first functional organosilicon compound to be resolved was the oc— naphthylphenylmethylsilane by Sommer and coworkers ^. it gave rise to numerous other functional optically active organosilicon compounds and allowed many stereochemical studies. Recent developments in asymmetric synthesis at silicon 3 now permits one to conduct an easy one-pot preparation of Sommer's compound starting from oc-naphthylphenylsilane. The advantages of this route have already been pointed out.^ Moreover, this method can be applied to various prochiral dihydrosilanes and permits access to chiral organosilicon compounds enriched in one enantiomer. PROCEDURE A. oc-Naphthylphenylsilane, oc-NpPhSiH? To a suspension of lithium aluminum hydride (7»6g, 0.2 mole) in 200 ml of anhydrous diethyl ether at 0eC is added dropwise a solution of oc- naphthylphenyldimethoxysilane 5 (29.4g, 0.1 mole) in 100 ml of diethyl ether. After
517 the addition is complete, the reaction mixture is allowed to warm to room temperature and stirred for 2 hr. The reaction mixture is then slowly added to a mixture of 200g of ice and 200 ml of a 4N HC1 solution. After hydrolysis the organic layer is collected and the aqueous layer extracted with 2 x 75 ml of diethyl ether. The combined extracts are then washed twice with 75 ml of water and dried over anhydrous sodium sulfate. The solvent is removed in vacuo and the residue is distilled. The «-naphthylphenylsilane (21.3g, 91$) is collected at 197°C/l8 mm Hg. oc-Naphthylphenylsilane is very soluble in most organic solvents. Its IR spectrum (CCI4) shows an intense absorption at 2130 cm -1 (i>Si-H)· I t s N M R spectrum (CCI4) exhibits a singlet at & = 5·2 ppm (Si-H) B. R( + ) oenaphthylphenylmethylsilane, R( + ) «-NpPhMeSiH (note 1,2) To a solution of tris(triphenylphosphine)rhodium chloride " (0.0465 g, 0.05 mmole) in 100 ml of dry degassed benzene is rapidly added a solution of (-) ephedrine (8.25 g, 50 mmoles) in 100 ml of benzene.
518 NOTES (1) S(-)o(-NpPhMeSiH is obtained in the same way using ( + )ephedrine. (2) Conventional Schlenck-type glassware 7 is used in this procedure and unless otherwise stated, all manipulations are carried out under nitrogen. (3) The total conversion of the starting «-naphthylphenylsilane can easily be checked by analysis of an aliquot by thin layer chromatography (TLC), using silica gel plates and a pentane-benzene (9:1) mixture as eluent. (4) At this stage unequal amounts of distereomers (I) and (II) are formed in quantitative yield. Their ratio, which reflect the optical yield of the asymetric induction, can be determined by NMR spectroscopy of a crude sample in CgDß (Si-H diastereomer (I) S - 5.9 Ppm diastereomer (II) S : 5·8 Ppm)♦ (5) The course of the reaction can be followed by analyzing an acid hydrolyzed aliquot by TLC (see note 2). The oc-naphthylphenylmethylsilane has almost the same Rf value as that of oc-naphthylphenylsilane. (6) The extracted aqueous layer contains (-)ephedrine hydrochloride. By addition of a 10# NaOH solution up to pH 10, and extraction with ether, the starting (-)ephedrine can be recovered. After drying the extracts over magnesium sulfate and evaporation of ether, the residue is distilled. (- ) Ephedrine (6.7g, m.p 35-36eC) is collected at 110eC/0.2 mm Hg. (7) One crystallization is usually sufficient to obtain R( + )oc-NpPhMeSiH with a high optical purity. If required, the compound can be recrystallized from pentane. (8) The procedure has been scaled up successfully starting from 0.1 mole of ot-naphthylphenylsilane. About 10g of optically pure R(+) «-NpPhMeSiH are routinely obtained with a yield in the range 40 to 50%. Using ( + ) ephedrine, on a smaller scale, S(-)w-NpPhMeSiH was isolated in a slightly better yield .^
REFERENCES 1. 2. 3. 4. 5. 35. 6. 7. 8. 9.
L.H. Sommer, Stereochemistry, Mechanism and Silicon, Mc Graw Hill, NewYork, 1965 : R.J.P. Corriu, C.Guerin and J.J.E. Moreau, Topics in Stereochemistry, 1£ (1984) 43. L.H Sommer, C.L. Frye, G.A. Parkerand K.W. Michael, J. Amer. Chem. S o c , 86 (1964) 3271. R.J.P. Corriu and J.J.E.Moreau, J. Organometal. Chem., 8^ (1975) 19 ; ibid., 120 (1976) 337 ; Nouv. J.Chim., 1 (1977) 71. R.J.P. Corriu and J.J.E.Moreau, Bull. Soc. Chim. Fr., (1975) 901. R.J.P. Corriu, G.F. Lanneau and G. Royo, J. Organometal. Chem., 35 (1972) J.A. Osborn, F.H. Jardine, J.F. Young and G. Wilkinson, J. Chem. S o c , A, (1966) 1711. D.F. Shriver, The Manipulation of Air-sensitive compounds, Mc Graw Hill, New-York 1969. L.H. Sommer and H. Fujimoto, J. Am. Chem. S o c , 22 (1968) 982. Y. Okaya and T. Ashida, Acta Cryst., 20 (1966) 46l.
THE SYNTHESIS OF R( + ) or S(-) oc-NAPHTHYLPHENYLMETHYLSILANE ROBERT J.P. CORRIU and JOEL J.E. MOREAU Institut de Chimie Fine - Universite des Sciences et Techniques du Languedoc 34060 Montpellier-cedex
L1AIH4 oc-NpPhSi(OMe) 2
MeVOH MeANHMe oc-NpPhSiH2
oc-NpPhSiH2
Et20
> (PPh3)3RhCl benzene
Ph I
Ph I + oc-Np - S i - H + H 2 I 0(-)Eph
I
1) MeMgBr 2) H 3 0 +
II
Ph
crystallization ->
oc-NpPhMeSi H
[
oc-Np - Si - Me
[«to + 34.5°
optical purity 96# yield W%
INTRODUCTION Stereochemistry at silicon has been widely studied over the past years. *■ The first functional organosilicon compound to be resolved was the oc— naphthylphenylmethylsilane by Sommer and coworkers ^. it gave rise to numerous other functional optically active organosilicon compounds and allowed many stereochemical studies. Recent developments in asymmetric synthesis at silicon 3 now permits one to conduct an easy one-pot preparation of Sommer's compound starting from oc-naphthylphenylsilane. The advantages of this route have already been pointed out.^ Moreover, this method can be applied to various prochiral dihydrosilanes and permits access to chiral organosilicon compounds enriched in one enantiomer. PROCEDURE A. oc-Naphthylphenylsilane, oc-NpPhSiH? To a suspension of lithium aluminum hydride (7»6g, 0.2 mole) in 200 ml of anhydrous diethyl ether at 0eC is added dropwise a solution of oc- naphthylphenyldimethoxysilane 5 (29.4g, 0.1 mole) in 100 ml of diethyl ether. After
517 the addition is complete, the reaction mixture is allowed to warm to room temperature and stirred for 2 hr. The reaction mixture is then slowly added to a mixture of 200g of ice and 200 ml of a 4N HC1 solution. After hydrolysis the organic layer is collected and the aqueous layer extracted with 2 x 75 ml of diethyl ether. The combined extracts are then washed twice with 75 ml of water and dried over anhydrous sodium sulfate. The solvent is removed in vacuo and the residue is distilled. The «-naphthylphenylsilane (21.3g, 91$) is collected at 197°C/l8 mm Hg. oc-Naphthylphenylsilane is very soluble in most organic solvents. Its IR spectrum (CCI4) shows an intense absorption at 2130 cm -1 (i>Si-H)· I t s N M R spectrum (CCI4) exhibits a singlet at & = 5·2 ppm (Si-H) B. R( + ) oenaphthylphenylmethylsilane, R( + ) «-NpPhMeSiH (note 1,2) To a solution of tris(triphenylphosphine)rhodium chloride " (0.0465 g, 0.05 mmole) in 100 ml of dry degassed benzene is rapidly added a solution of (-) ephedrine (8.25 g, 50 mmoles) in 100 ml of benzene.
518 NOTES (1) S(-)o(-NpPhMeSiH is obtained in the same way using ( + )ephedrine. (2) Conventional Schlenck-type glassware 7 is used in this procedure and unless otherwise stated, all manipulations are carried out under nitrogen. (3) The total conversion of the starting «-naphthylphenylsilane can easily be checked by analysis of an aliquot by thin layer chromatography (TLC), using silica gel plates and a pentane-benzene (9:1) mixture as eluent. (4) At this stage unequal amounts of distereomers (I) and (II) are formed in quantitative yield. Their ratio, which reflect the optical yield of the asymetric induction, can be determined by NMR spectroscopy of a crude sample in CgDß (Si-H diastereomer (I) S - 5.9 Ppm diastereomer (II) S : 5·8 Ppm)♦ (5) The course of the reaction can be followed by analyzing an acid hydrolyzed aliquot by TLC (see note 2). The oc-naphthylphenylmethylsilane has almost the same Rf value as that of oc-naphthylphenylsilane. (6) The extracted aqueous layer contains (-)ephedrine hydrochloride. By addition of a 10# NaOH solution up to pH 10, and extraction with ether, the starting (-)ephedrine can be recovered. After drying the extracts over magnesium sulfate and evaporation of ether, the residue is distilled. (- ) Ephedrine (6.7g, m.p 35-36eC) is collected at 110eC/0.2 mm Hg. (7) One crystallization is usually sufficient to obtain R( + )oc-NpPhMeSiH with a high optical purity. If required, the compound can be recrystallized from pentane. (8) The procedure has been scaled up successfully starting from 0.1 mole of ot-naphthylphenylsilane. About 10g of optically pure R(+) «-NpPhMeSiH are routinely obtained with a yield in the range 40 to 50%. Using ( + ) ephedrine, on a smaller scale, S(-)w-NpPhMeSiH was isolated in a slightly better yield .^
REFERENCES 1. 2. 3. 4. 5. 35. 6. 7. 8. 9.
L.H. Sommer, Stereochemistry, Mechanism and Silicon, Mc Graw Hill, NewYork, 1965 : R.J.P. Corriu, C.Guerin and J.J.E. Moreau, Topics in Stereochemistry, 1£ (1984) 43. L.H Sommer, C.L. Frye, G.A. Parkerand K.W. Michael, J. Amer. Chem. S o c , 86 (1964) 3271. R.J.P. Corriu and J.J.E.Moreau, J. Organometal. Chem., 8^ (1975) 19 ; ibid., 120 (1976) 337 ; Nouv. J.Chim., 1 (1977) 71. R.J.P. Corriu and J.J.E.Moreau, Bull. Soc. Chim. Fr., (1975) 901. R.J.P. Corriu, G.F. Lanneau and G. Royo, J. Organometal. Chem., 35 (1972) J.A. Osborn, F.H. Jardine, J.F. Young and G. Wilkinson, J. Chem. S o c , A, (1966) 1711. D.F. Shriver, The Manipulation of Air-sensitive compounds, Mc Graw Hill, New-York 1969. L.H. Sommer and H. Fujimoto, J. Am. Chem. S o c , 22 (1968) 982. Y. Okaya and T. Ashida, Acta Cryst., 20 (1966) 46l.