REGIOCONTROLLED AND STEREOCONTROLLED FORMATION OF CHIRAL EPOXY OXAZOLIDINES VIA BROMOCARBAMATION OF N-BOC ALKENYL OXAZOLIDINES - APPLICATION TO ASYMMETRIC-SYNTHESIS
C. Agami et al., REGIOCONTROLLED AND STEREOCONTROLLED FORMATION OF CHIRAL EPOXY OXAZOLIDINES VIA BROMOCARBAMATION OF N-BOC ALKENYL OXAZOLIDINES - APPLICATION TO ASYMMETRIC-SYNTHESIS, Journal of organic chemistry, 62(7), 1997, pp. 2106-2112
Treatment of alpha-alkenyl N-Boc oxazolidines with N-bromosuccinimide
leads to epoxy oxazolidines via a bromocyclocarbamation reaction which
is completely stereoselective. Action of sodium azide an these epoxid
es, followed by a few functional group manipulations, eventually affor
ds chiral beta-amino alcohols which are intermediates for the enantios
elective synthesis of bioactive products: the anti side chain of taxol
and a hydroxyethylamine isostere. Both the bromocarbamation cyclizati
on and the nucleophilic cleavage of epoxides are totally regioselectiv
e. AM1 calculations suggest that this selectivity is controlled by the
positive charge distribution at the electrophilic centers.