Bromination of sugar enones and enonolactones

• Published in: Carbohydrate research 1995-04, Vol.269 (1), p.99-109
• Main Authors: Di Nardo, Christían, Varela, Oscar, de Lederkremer, Rosa M., Baggio, Ricardo F., Vega, Daniel R., Garland, María T.
• Format: Article
• Language: English
• Subjects: Bromination; Enones; Enonolactones; Sugar enones and enonolactones
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/0008-6215(94)00352-G

Bromination of 2,4,6- tri-O- benzoyl-3- deoxy- d-erytro- hex-2- enono-1,5- lactone (1) took place diastereoselectively to afford a single product: 2,4,6- tri-O- benzoyl-2,3- dibromo-3- deoxy- d- altrono-1,5- lactone (2). The configuration of C-2 and C-3 was determined as R,R by NMR spectroscopy and taking into account considerations of the stereochemical course of the bromination. The configuration of 2 was confirmed by X-ray analysis, which also revealed that the conformation of the lactone ring consists of a 4H 3( d) distorted half-chair. The bromine addition to 2,5,6,7- tetra-O- benzoyl- d-arabino- hept-2- enono-1,4- lactone (5), readily prepared by DBU-promoted elimination from the perbenzoylated lactone derivative 4, was also diastereoselective and led to the dibromo derivative 6, whose configuration for C-2 and C-3 was assigned as S,S. Bromination of the α,β-unsaturated carbonyl system of 2-propyl 6-O- acetyl-3,4- dideoxy-α- d-glycero- hex-3- enopyranosid-2- ulose (7) afforded an unsaturated monobromo derivative: 2-propyl 6-O- acetyl-3- bromo-3,4- dideoxy-α- d-glycero- hex-3- enopyranosid-2- ulose (8), suggesting that dehydrobromination occurred after addition of bromine.