SYNTHESIS AND REACTIONS OF 1,2-CYCLOPROPANATED SUGARS

Diastereospecific cyclopropanation of glycals 1, 2, 3, 4, and 41 was c arried out using either dihalocarbene addition or zinc-carbenoid addit ion to yield 1,2-cyclopropanated sugars. Dichloro- and dibromocarbenes added stereoselectively anti to the C-3 benzyloxy group, whereas (und er Simmons-Smith conditions) the cyclopropanes were formed syn to the same substituent. The reactions of these 1,2-cyclopropanated sugars to provide either ring expanded glycosides or C-2-branched chain glycosi des were explored. Solvolytic ring expansion of 1,2-dibromocyclopropan ated sugars with K2CO3 in refluxing methanol yielded the corresponding chiral oxepins 20-22. Electrophilic ring openings of parent cycloprop anes (14 and 17 derived from glucal 1) were carried out with different electrophiles to give functionalized 2-deoxy-2-C-branched chain glyco sides. The ring openings of 14 in different solvents resulted in both alpha- and beta-anomers, whereas 17 gave exclusively the alpha-anomer.