Stereodivergent synthesis of 5a-carba-hexopyranoses from carbohydrates via 6-exo-dig radical cyclization: preparation of 5a-carba-β-d-manno-, α-d-allo-, β-l-talo- and α-l-gulopyranose pentaacetates from d-mannose

✍ Scribed by Ana M. Gómez; Eduardo Moreno; Gerardo O. Danelón; Serafı́n Valverde; J.Cristóbal López

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 878 KB
• Volume: 14
• Category: Article
• ISSN: 0957-4166
• DOI: 10.1016/s0957-4166(03)00532-9

✦ Synopsis

Four carbasugars, 5a-carba-b-D-manno-, a-D-allo-, b-L-taloand a-L-gulopyranose pentaacetates, have been prepared in a stereodivergent manner from D-mannose. Alkynyl derivatives of 2,3:4,6-di-O-isopropylidene-D-mannopyranose, which are prepared by homologation at C-1, by reaction with phenyl acetylide, undergo a 6-exo-dig radical cyclization, from a radical located at C-5, to yield a mixture of highly functionalized cyclohexanes. Some of these compounds, after transformation of their exocyclic double bond in a hydroxy function, were correlated with polyhydroxylated cyclohexanes, which were then selectively deoxygenated either at position C-4 or C-5a (carbohydrate numbering) to afford carbasugars of the D-or L-series.