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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
Author(s) -
Gómez Ana M.,
Moreno Eduardo,
Valverde Serafín,
López J. Cristóbal
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300339
Subject(s) - chemistry , deoxygenation , stereochemistry , stereoselectivity , moiety , ozonolysis , double bond , total synthesis , mannose , yield (engineering) , organic chemistry , catalysis , materials science , metallurgy
The 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. Ozonolysis of the exocyclic double bond in the latter generated cyclohexanones which, upon stereoselective reduction of the carbonyl moiety followed by site‐selective deoxygenation either at position C‐4 or C‐5a (parent carbohydrate numbering), afforded the title carbasugars. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)