1,2-Additions aldehydes/ketones, chlorotrimethylsilane

Hydroxyphosphonium salts and l-(trimethylsiloxy)phosphonium salts are obtained219 from the addition of small-sized phosphines (PMe3 and PEt3) to a carbonyl group of ketones and aldehydes, in the presence of chlorotrimethylsilane or of the mixture ace-tone/bromine, which is a source of anhydrous HBr. 

It should be noted that several procedures are available for the preparation of l-(trimethylsilyloxy)cyclohexene. In an original report252 it was prepared by heating a dimethylformamide solution of cyclohexanone under reflux with chlorotrimethylsilane in the presence of triethylamine. This procedure is generally satisfactory for aldehydes and symmetrical ketones, or ketones which can enolise in one direction only. The method described in Expt 5.214 employs lithium sulphide as an additive to increase the silylating power of the chlorotrimethylsilane, so that the reaction proceeds at room temperature acetonitrile is used as the solvent.253... 

The nucleophilic addition of a carbanion to an aldehyde or a ketone having a conjugated double bond and the subsequent dehydration sequence (Knoevenagei reaction) is a popular method for generating dienes and polyenes (equation 37). This reaction takes place efficiently and stereoselectively, when LDA is used as a base in the presence of chlorotrimethylsilane (equation 38). Knoevenagei condensation was a key reaction during many classical carotenoid syntheses. Recently, Seltzer and coworkers used the dimefiiyl acetal of acetylacetaldehyde for aldol condensation with a Cis-aldehyde, to generate the tetraenyl ketone acetal (equation 39). ... 

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