Opening of tartrate acetals using dialkylboron bromide: evidence for stereoselectivity downstream from ring fission.
Johnson-type acetals derived from dimethyl tartrate give, after opening with Me(2)BBr and cuprate displacement, secondary alcohols with high diastereoselectivity (>30:1). The mechanism proposed for the induction of diastereoselectivity is downstream from the ring fission. It implies a direct participation of the Lewis acid as a source of nucleophile and the stereospecific transformation of the resulting bromo acetal through an invertive and temperature-dependent process. The acetals are prepared by reaction of the desired aldehyde with dimethyl tartrate. Removal of the auxiliary is accomplished through SmI(2) reduction or by an addition-elimination protocol using methoxide.
Guindon
Yvan
Y
Boehringer Ingelheim (Canada) Ltd., Bio-Méga Research Division, 2100 rue Cunard, Laval Québec, Canada H7S 2G5.
Ogilvie
William W
WW
Bordeleau
Josée
J
Cui
Wei Li
WL
Durkin
Kathy
K
Gorys
Vida
V
Juteau
Hélène
H
Lemieux
René
R
Liotta
Dennis
D
Simoneau
Bruno
B
Yoakim
Christiane
C