Hydroxylated C-branched pyrrolidines, C-branched prolines and C-branched piperidines from a 2-C-methyl sugar lactone; efficient azide displacement of a tertiary triflate with inversion of configuration

The versatility of 3,4-O-isopropylidene-2-C-methyl-d-arabinonolactone [from d-erythronolactone] as a chiron for complex piperidines and pyrrolidines is illustrated by the synthesis of (2R,3S,4S)- and (2R,3S,4R)-dihydroxy-2-C-methyl prolines, 1,4-dideoxy-1,4-imino-4-C-methyl-l-ribitol and 1,4-dideoxy-1,4-imino-4-C-methyl-l-arabinitol, and isofagomine derivatives; the enantiomeric series is equally accessible from l-erythronolactone.