A Stereodivergent Approach to 5a‐Carba‐α‐D‐gluco‐, ‐α‐D‐galacto and ‐β‐L‐gulopyranose Pentaacetates from D‐Mannose, Based on 6‐exo‐dig Radical Cyclization and Barton−McCombie Radical Deoxygenation

Abstract

Keywords: Carbohydrates / Radical cyclization / Radical deoxygenation / Synthesis design / -MannoseThe three carbasugars, 5a-carba-α-D-gluco-, -α-D-galacto and -β-L-gulopyranose pentaacetates 42, 35 and 28 respectively, have been prepared in a stereodivergent manner from D-mannose. Alkynyl derivatives of 2,3:4,6-di-O-isopropylidene-D-mannopyranose, which are homologated at C-1 by reaction with trimethylsilylacetylide, undergo a 6-exo-dig radical cyclization, from a radical located at C-5, to yield a mixture of highly functionalized exo-methylenecyclohexanes.

Synthesis and Conformational and Biological Aspects of Carbasugars

“…Along these lines, Gómez et al applied their methodology to the preparation of three carbasugars from a single polyoxygenated cyclohexanone ( A , Scheme ). They exploited the deoxygenation (either at C 5a or at C 4 ) of the two diastereoisomers ( B , C , Scheme ) originating from the stereoselective reduction of the C 5a ketone in compound A .…”

Site-Selective Catalysis of Phenyl Thionoformate Transfer as a Tool for Regioselective Deoxygenation of Polyols

“…The deoxygenation of alcohols is a fundamental transformation in organic synthesis . The development of catalysts that could selectively remove a hydroxyl group from a polyol structure would be a particularly advantageous method in medicinal chemistry settings because one might use the technique to obtain deoxyanalogs of polyol agents without elaborate syntheses or complicated protecting group schemes (Scheme ) . To develop such methodology, we began an investigation of site-selective transfer of the thiocarbonyl group as a prelude to substrate deoxygenation, utilizing the venerable Barton−McCombie reaction .…”

Synthesis of chiral cyclohexanes and carbasugars by 6-exo-digradical cyclisation reactions

“…With the availability of the iodides 7a and 7b we investigated their radical cyclisation reactions. Treatment of 7a with tri- n -butyltin hydride and AIBN in refluxing benzene afforded ( Scheme 2 ) the 6- exo -cyclisation [ 25 – 28 ] products 10 in 93% yield as an inseparable mixture of E and Z geometric isomers in a ratio of 1:1.6 as determined by 1 H NMR analysis. The diastereomer 7b on similar treatment underwent a 6- exo -cyclisation and afforded the corresponding cyclohexanes 11 and 12 in 61% yield.…”