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A convergent strategy for the synthesis of beta -carba-galacto-disaccharide
s is illustrated by the preparation of 1 and 4, from a central "glycone" co
mponent 22, and the corresponding "aglycone" segments, monosaccharide alcoh
ols, 23a or 23b, The key step is the formation of the carbasugar ring via a
n oxocarbenium ion-enol ether cyclization.