Palladium(O)-catalyzed allylic substitution with allylic alkoxides as substrates

Abstract

A new method has been developed which allows palladium(O)-catalyzed allylic substitution to occur between allylic alcohols and anionic C-nucleophiles: on reaction with Ph 3B, the allylic alkoxide 2 is first converted situ into the more reactive species 3 which then undergoes a Pd(O)-catalyzed reaction with lithio diethyl malonate via the η 3-complex 6. Allylic alkoxides can be generated in situ either by deprotonation of the corresponding alcohol ( 1 → 2, e.g. with BuLi), via a vinylmagnesium halide addition to the corresponding aldehyde ( 4 + 5 → 2), or by hydride reduction (DIBAH) of α,β-unsaturated ketones ( 31 → 32). The whole sequence can be carried out as a one-pot procedure and is suitable for sensitive allylic alcohols that might be difficult to handle in pure state. While allylic alcohols ( 7 and 18) and their allylic isomers ( 14 and 15) give mixtures of mono- and bis-allylated products with LiCH(CO 2Et) 2, exclusive monoallylation has been observed for secondary alcohols ( 21, 23, and 26).