1.4- Hydrosilylation enol ether preparation

As an alternative to enolization and addition of a silyl halide or trillate, silyl enol ethers may be prepared by the 1,4-hydrosilylation of an a,3-unsaturated ketone. This can be done by using a silyl hydride reagent in the presence of a metal catalyst. Metal catalysts based on rhodium or platinum are most effective and provide a regiospecific approach to silyl enol ethers (1.25). 

E-Alkenylpentafluorosilicates [e.g. (31)], which are readily obtained from acetylenes by hydrosilylation, are useful intermediates for the preparation of -enol ethers (32)" and thiocyanates (33). Both processes are compatible with cyano and ester groups, and when terminal silicates are used stereoselectivity is very high (>99%). Primary alcohols give the highest yields of enol ethers, whereas tertiary alcohols do not react, and allylic alcohols give the particularly useful allyl vinyl ethers. 

Transition metal catalyzed hydrosilylation of a, -unsaturated ketones and aldehydes (78) proceeds in a 1,4- and/or 1,2-fashion to give enol silyl ethers (79) (or the saturated carbonyl compounds 80 after acidic work-up) and/or allyl silyl ethers (81) (or allyl alcohols 82), respectively (equation 54). Monohydrosilanes combined with a Pt or Rh catalyst prefer 1,4-addition. This reaction is an alternative meth for the preparation of enol silyl ethers (79). Diphenylsilane with [RhCl(PPh3)3] catalyst reduces the car-... 

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