De novo synthesis of racemic spirocyclopropane-annelated 2-deoxyhexose derivatives

High-pressure-induced inverse-electron-demand hetero-Diels-Alder reactions of ethyl trans-4-ethoxy-2-oxo-3-butenoate (2a) and methyl trans-4-benzyloxy-2-oxo-3-butenoate (2b) with benzyl (cyclopropylidenemethyl) ether (1) each yielded mixtures of two separable diastereomeric esters 7a (64%) and 7b (80%) which, in three subsequent steps, led to the 3-ethylated and 3-benzylated alpha- and beta-anomeric benzyl spiro[2-deoxy-(D,L)-arabino-hexopyranoside-2,1'-cyclopropanes] alpha-10a,b and beta-10a,b, respectively. The relative configuration of beta-10a was proved by an X-ray crystal structure analysis. Deprotection of beta-10b was achieved by Pd-catalyzed hydrogenation in dimethylacetamide leading to spiro[2-deoxy-alpha/beta-2-(D,L)-arabino-hexopyranoside-2,1'-cyclopropane] (4).