Si4 Alkene synthesis Peterson olefination

P-Hydroxysilanes are key compounds in the application of organosilicon chemistry to the synthesis of alkenes. Three methods of generating them are described below. 

Note that the epoxide in Equation Si4.4 is opened at its most hindered end as the silyl group promotes substitution a to itself (see also Equations Si5.18 and 5.19). 

Addition of hydride sources or organometallic reagents to (3-ketosilanes 

The antiperiplanar relationship of the trimethylsilyl group and the hydroxy group places the bonds to be broken or formed in the same plane and thus maximizes orbital overlap. 

Recall that the Felkin-Anh model predicts the preferred approach of a nucleophile to a carbonyl group bearing a chiral centre. The model places the most bulky group on the chiral centre (L) perpendicular to the plane of the carbonyl and its substituent (R), and the least bulky group on the chiral centre (S) adjacent to the carbonyl substituent (R). The nucleophile then prefers to approach the carbonyl past the smallest substituent on the chiral centre. 

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