Alkoxide-Induced Succinate Ester Formation from Alcohols and Bis(trimethylsilyl) 1,2-Bisketene.
Reaction of the 1,2-bisketene (Me(3)SiC=C=O)(2) (1) with alcohols (ROH) catalyzed by LiOR gives rapid and efficient conversion to mixtures of the meso and dl succinates (Me(3)SiCHCO(2)R)(2) (4). There is a change in selectivity with the dl/meso ratio varying from 18/82 with MeOH to 92/8 for t-BuOH. This procedure occurs with minimal desilylation, which is the predominant path in the uncatalyzed reaction. Preferential attack of lithium alkoxides on the carbonyl carbon of ketenes induced by lithium coordination to the ketenyl oxygen is proposed to account for the low extent of desilylation. The stereochemical assignments of the meso and dl configurations are based upon vicinal H,H coupling constants both from a mixed succinate ester and also from (13)C,(1)H satellite spectra and are confirmed by X-ray structure determinations. Reaction of 1 with catechols 10-12 catalyzed by n-BuLi leads to ortho esters 15-18, while reaction with the perhalo catechols 13 and 14 gives isolable hydroxaryl ketenyl esters 19 and 20.
Egle
Ian
I
Department of Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3H6.
Lai
Wing-Yan
WY
Moore
Patrick A.
PA
Renton
Paul
P
Tidwell
Thomas T.
TT
Zhao Dc
Da-chuan