Trialkylsilanes, chiral

Hydrosilylation of 1,6-dienes accompanied by cyclization giving a five-membered ring system is emerging as a potential route to the synthesis of functionalized carbocycles.81,81a,81b 82 As its asymmetric version, diallylmalonates 86 were treated with trialkylsilane in the presence of a cationic palladium catalyst 88, which is coordinated with a chiral pyridine-oxazoline ligand. As the cyclization-hydrosilylation products, //ww-disubstituted cyclopentanes 87 were obtained with high diastereoselectivity (>95%), whose enantioselectivity ranged between 87% and 90% (Scheme 25).83 83a... 

Kumada et al. have examined a number of chiral ferrocenylphosphines as ligands for asymmetric reactions catalyzed by transition metals. They are of interest because they contain a planar element of chirality as well as an asymmetric carbon atom. They were first used in combination with rhodium catalysts for asymmetric hydrosilylation of ketones with di- and trialkylsilanes in moderate optical yields (5-50%). High stereoselectivity was observed in the hydrogenation of a-acetamidoacrylic acids (equation 1) with rhodium catalysts and ferrocenylphosphines. ... 

It has also been demonstrated that trialkylsilanes, which are poor radical-based reducing agents due to their low hydrogen donation abilities [79], can reduce alkyl halides and xanthates (equation (36)) to the corresponding hydrocarbons in the presence of a catalytic amount of an alkanethiol [80]. The reaction consists of a chain process in which the key propagation step is the hydrogen transfer from the silane to the alkanethiyl radical. This approach has also been used for the hydrosilylation of chiral alkenes by Ph2SiH2 [81]. 

In parallel with the developments involving chiral allylation reagents, there have been a number of exciting reports of catalytic enantioselective processes [24, 30, 32, 119]. To date, these have most efficiently been achieved for chiral Lewis acid catalysts combined with type 2 allyl trialkylsilanes and trialkyl-stannanes. In addition, there have also been recent impressive reports of the use of Lewis basic catalysts with aUyl trihalosilanes. 

---