Hydrosilylation asymmetric syntheses

Yamano T, Taya N, Kawada M, Huang T, Imamoto T (1999) Tetrahedron Lett 40 2577 Brunner H, Nishiyama H, Itoh K (1993) Asymmetric hydrosilylation. In Ojima I (ed) Catalytic asymmetric synthesis. Wiley-VCH, New York, chap 6 Sawamura M, Kuwano R, Ito Y (1994) Angew Chem, Int Ed Engl 33 111 Kuwano R, Uemura T, Saitoh M, Ito Y (1999) Tetrahedron Lett 40 1327 Hayashi T (1993) Asymmetric allylic substitution and grignard cross-coupling. In Ojima I (ed) Catalytic asymmetric synthesis. WUey-VCH, New York, chap 7-1 Trost BM, Vranken DLV (1996) Chem Rev 96 395 Consiglio G,Waymouth RM (1989) Chem Rev 89 257... 

Asymmetric hydrosilylation can be extended to 1,3-diynes for the synthesis of optically active allenes, which are of great importance in organic synthesis, and few synthetic methods are known for their asymmetric synthesis with chiral catalysts. Catalytic asymmetric hydrosilylation of butadiynes provides a possible way to optically allenes, though the selectivity and scope of this reaction are relatively low. A chiral rhodium complex coordinated with (2S,4S)-PPM turned out to be the best catalyst for the asymmetric hydrosilylation of butadiyne to give an allene of 22% ee (Scheme 3-20) [59]. 

A hydrosilylation/cyclization process forming a vinylsilane product need not begin with a diyne, and other unsaturation has been examined in a similar reaction. Alkynyl olefins and dienes have been employed,97 and since unlike diynes, enyne substrates generally produce a chiral center, these substrates have recently proved amenable to asymmetric synthesis (Scheme 27). The BINAP-based catalyst employed in the diyne work did not function in enyne systems, but the close relative 6,6 -dimethylbiphenyl-2,2 -diyl-bis(diphenylphosphine) (BIPHEMP) afforded modest yields of enantio-enriched methylene cyclopentane products.104 Other reported catalysts for silylative cyclization include cationic palladium complexes.105 10511 A report has also appeared employing cobalt-rhodium nanoparticles for a similar reaction to produce racemic product.46... 

The asymmetric hydrosilylation that has been most extensively studied so far is the palladium-catalyzed hydrosilylation of styrene derivatives with trichlorosilane. This is mainly due to the easy manipulation of this reaction, which usually proceeds with perfect regioselectivity in giving benzylic silanes, 1-aryl-1-silylethanes. This regioselectivity is ascribed to the formation of stable 7t-benzylpalladium intermediates (Scheme 3).1,S Sa It is known that bisphosphine-palladium complexes are catalytically much less active than monophosphine-palladium complexes, and, hence, asymmetric synthesis has been attempted by use of chiral monodentate phosphine ligands. In the first report published in 1972, menthyldiphenylphosphine 4a and neomenthyldiphenylphosphine 4b have been used for the palladium-catalyzed reaction of styrene 1 with trichlorosilane. The reactions gave l-(trichlorosilyl)-l-phenylethane 2 with 34% and 22% ee, respectively (entries 1 and 2 in Table l).22 23... 

The palladium-catalyzed asymmetric hydrosilylation of styrenes has been applied to the catalytic asymmetric synthesis of l-aryl-l,2-diols from arylacetylenes (Scheme 6).46 Thus, ( )-l-aryl-2-(trichlorosilyl)ethenes, which are readily generated by platinum-catalyzed hydrosilylation of arylacetylenes, were treated with trichlorosilane and the palladium catalyst coordinated with MOP ligand 12f to give 1 -aryl-1,2-bis(silyl)ethanes, oxidation of which produced the enantiomerically enriched (95-98% ee) 1,2-diols. 

It is well documented that hydrosilylation of alkyl-substituted terminal olefins catalyzed by transition metal complexes proceeds with high regioselectivity in giving linear hydrosilylation products which do not possess a stereogenic carbon center.2 It follows that the asymmetric synthesis by use of the hydrosilylation of alkyl-substituted... 

In 2001, a palladium-catalyzed asymmetric hydrosilylation of 4-substituted-but-l-en-3-ynes (146) was reported by Hayashi and co-workers [115]. It was found that a monodentate bulky chiral phosphine, (S)-(R)-bisPPFOMe, was effective for the asymmetric synthesis of the axially chiral allenes 147 and up to 90% ee was achieved (Scheme 3.75). The bulky substituent at the 4-position in 146 is essential for the selective formation of the allene 147 the reaction of nC6H13C=CCH=CH2 gave a complex mixture of hydrosilylation products which consisted of <20% of the allenylsilane. 

Scheme 4.67 Asymmetric synthesis of allene 260 by rhodium-catalyzed hydrosilylation of diyne 258.

Until 1968, not a single nonenzymic catalytic asymmetric synthesis had been achieved with a yield above 50%. Now, barely 15 years later, no fewer than six types of reactions can be carried out with yields of 75-100% using amino acid catalysts, i.e., catalytic hydrogenation, intramolecular aldol cyclizations, cyanhydrin synthesis, alkylation of carbonyl compounds, hydrosilylation, and epoxidations. 

Certain imines (26) ketoximes (27) are hydrosilylated by a DIOP-Rh complex to give, after hydrolysis, cyclic or acyclic amines in moderate optical yield (Scheme 9). An asymmetric synthesis of 1,2,3,4-tetrahy-dropapaverine in 39% ee and related compounds is feasible. 

Nishiyama H, Itoh K (2000) Asymmetric hydrosilylation and related reactions. In Ojima I (ed) Catalytic asymmetric synthesis, chap 2,2nd edn. Wiley-VCH, New York... 

In this chapter, recent advances in asymmetric hydrosilylations promoted by chiral transition-metal catalysts will be reviewed, which attained spectacular increase in enantioselectivity in the 1990s [1], After our previous review in the original Catalytic Asymmetric Synthesis, which covered literature through the end of 1992 [2], various chiral Pn, Nn, and P-N type ligands have been developed extensively with great successes. In addition to common rhodium and palladium catalysts, other new chiral transition-metal catalysts, including Ti and Ru complexes, have emerged. This chapter also discusses catalytic hydrometallation reactions other than hydrosily-lation such as hydroboration and hydroalumination. 

Since the catalytic activity of the Wilkinson complex, RhCl(PPh3)3. for the hydrosilylation of ketones was discovered, the application of this reaction to asymmetric synthesis has been studied... 

Applications of the intramolecular hydrosilylation to catalytic asymmetric synthesis will be discussed in Section V (vide infra). 

Catalytic asymmetric intramolecular hydrosilylation of dialkyl- and diarylsilyl ethers of bis(2-propenyl)methanol (245) catalyzed by (R, R)-DIOP-Rh or (R)-binap-Rh complex, followed by Tamao oxidation, gives (2S, 3R)-2-methyl-4-pentene-l,3-diol (247) with 71-93% ee and excellent syn selectivity (syn/anti = 95/5- > 99/1) (equation 96)249. The enantioselectivity of this reaction depends on the bulkiness of the silyl moiety, i.e. the bulkier the substituent, the higher is the enantiopurity of the product, except for the case of 2-MeCgH4 R = Me, 80% ee (binap-Rh) R = Ph, 83% ee (DIOP-Rh) R = 2-McC.fiI I4, 4% ee (DIOP-Rh) R = 3-MeC6H4, 87% ee (DIOP-Rh) R = 3,5-Me2C6H3, 93% ee (DIOP-Rh). This methodology is successfully applied to the asymmetric synthesis of versatile poly oxygenated synthetic intermediate 249 (equation 97)249. 

Asymmetric Synthesis of Alcohols by Hydrosilylation of Ketones A Comparison of an Insolubilized (+) -DIOP Catalyst vs a Solution (+)-DIOP Catalysta... 

Review R. E. Merrill, Asymmetric synthesis using chiral Phosphine ligands, Reaction Design Corp., Hillside, N.J., 1979. This review covers the literature to mid-1979 (234 references). It discusses mechanisms and applications to asymmetric hydrogenation, hydrosilylation, hydroformylation and alkylation. 

The asymmetric hydrosilylation of a-methylstyrene with methyldi-chlorosilane has been catalyzed by (/ )-benzylmethylphenylphosphine complexes of platinum(II) 302) or nickel(II) 304) to give a 5 or 17.6% excess of one enantiomer in the addition product, 2-phenylpropyl-methyldichlorosilane. The corresponding palladium(II) complexes were, however, only slightly useful for asymmetric synthesis in hydrosilylation of olefins. Nevertheless, palladium(II) complexes of methyldiphenyl-phosphine or epimeric neomethyldiphenylphosphine, where the dissymmetry is remote from the phosphorus, are especially useful for the induction of asymmetry in the hydrosilylation of styrene and some cyclic conjugated dienes 199). A similar procedure has been used for... 

H. Takaya, T. Ohta, R. Noyori, in Asymmetric Hydrogenation in Catalytic Asymmetric Synthesis, I. Ojima, ed., VCH Publishers, New York, 1993, p. 1 H. Brunner, H. Nishiyama, K. Itoh, Asymmetric hydrosilylation in Catalytic Asymmetric Synthesis, I. Ojima, ed., VCH Publishers, New York, 1993, p. 303. 

This volume begins with two procedures in the area of catalytic asymmetric synthesis. The first procedure describes the synthesis of (R)-2-Dl PH ENYLPHOSPHI NO-2 -METHOXY-1,1 -BINAPHTHYL (MOP), a chiral ligand that has proven very useful in palladium-catalyzed hydrosilylation of olefins and palladium-catalyzed reduction of allylic esters by formic acid. The next procedure describes the catalytic asymmetric synthesis of nitroaldols using a chiral LANTHANUM-LITHIUM-BINOL COMPLEX, illustrated by the synthesis of (2S,3S)-2-NITRO-5-PHENYL-1,3-PENTANEDIOL. 

Asymmetric synthesis through a selective monofunctionalization of enantiotop-ic positions is considered as being one of the most attractive strategies for the one-step construction of multiple chiral carbon centers [34,35]. Asymmetric hydrosilylation of norbornene (21) was first attempted by use of a palladium catalyst coordinated with ferrocenylmonophosphine, (1 )-(S)-PPFA (15a) [28]. The... 

Palladium-catalyzed hydrosilylation of 1,3-dienes is one of the important synthetic methods for allylic silanes, and considerable attention has been directed to the asymmetric synthesis of the latter by catalytic methods [9]. Optically active allyhc silanes have been used as chiral allylating reagents in S reactions with electrophiles, typically aldehydes [38,39]. In the presence of Pd catalysts the reaction with hydrosilanes containing electron-withdrawing atoms or substituents on sihcon usually proceeds in a 1,4-fashion giving allyHc silanes [40,41]. Asymmetric hydrosilylation of cyclopentadiene (29) forming optically active 3-silylcyclopentene (30) has been most extensively studied (Scheme 13). In the first report, hydrosilylation of cyclopentadiene (29) with methyldichlorosilane in the presence of 0.01 mol % of palladium-(l )-(S)-PPFA (15a) as a catalyst gave... 

---