BROMINATION OF SUGAR ENONES AND ENONOLACTONES

Bromination of O-benzoyl-3-deoxy-D-erytro-hex-2-enono-1,5-lactone (1) took place diastereoselectively to afford a single product: benzoyl-2, 3-dibromo-3-deoxy-D-altrofio-1,5-lactone (2). The configuration of C-2 and C-3 was determined as R,R by NMR spectroscopy and taking into acc ount considerations of the stereochemical course of the bromination. T he configuration of 2 was confirmed by X-ray analysis, which also reve aled that the conformation of the lactone ring consists of a H-4(3)(D) distorted half-chair. The bromine addition to tetra-O-benzoyl-D-arabi no-hept-2-enone-1,4-lactone (5), readily prepared by DBU-promoted elim ination from the perbenzoylated lactone derivative 4, was also diaster eoselective and led to the dibromo derivative 6, whose configuration f or C-2 and C-3 was assigned as S,S. Bromination of the alpha,beta-unsa turated carbonyl system of 2-propyl -dideoxy-alpha-oglycero-hex-3-enop yranosid-2-ulose (7) afforded an unsaturated monobromo derivative: 2-p ropyl dideoxy-alpha-D-glycero-hex-3-enopyranosid-2-ulose (8), suggesti ng that dehydrobromination occurred after addition of bromine.