Activation of silicon-hydrogen, silicon-oxygen, silicon-nitrogen bonds in heterogeneous phase : Some new methods in organic synthesis

Abstract

Anionic activation of Si-H, Si-O and Si-N bonds by fluoride ions under heterogeneous conditions is reported: Si-H activated by KF or CsF is a very powerful and selective reducing reagent; the carbonyl group of aldehydes, ketones or esters can be reduced without reduction of other functional groups (C&z.dbnd;C, NO 2, Br, amido). Furthermore, selective reductions of aldehydes in the presence of ketones and ketones in the presence of carboxylic esters are also possible. CsF in the presence of Si(OR) 4 is found to be very efficient in promoting Michael additions of monoketones and arylacetonitriles on different kinds of Michael acceptors such as ⇌, β unsaturated ketones, esters, nitriles and even amides. This constitutes an extension of Michael reaction since the addition occurs even with crowded ketones. N, N bis(silyl)enamines activated by fluoride ions react with carbonyl compounds and provide an interesting route to 2-aza-1, 3 dienes.