摘要:
Mannosylations using the new conformationally restricted donor phenyl 2,3-di-O-benzyl-4,6-O-(di-tert-butylsilylene)-1-thio-alpha-D-mannopyranoside (6) have been found to be beta-selective with a variety of activation conditions. The simplest activation conditions were NIS/TfOH, in which case it is proposed that the beta-mannoside is formed from beta-selective glycosylation of the oxocarbenium ion 25 in a B-2,B-5 conformation.