Direct Conversion of 5,6-Unsaturated Hexopyranosyl Compounds to Functionalized Cyclohexanones

Abstract

Hexopyranoid glycosides and glycosyl esters that have an exocyclic double bond at C-5 (with or without an O-linked substituent at C-6) can be converted directly, efficiently and under mild conditions to cyclohexanone derivatives of the inosose or deoxyinosose categories. Usually mercury(II) salts are used to promote the process, but Pd(II) compounds can also be employed. Carbon-6 of the starting materials bonds to C-1 of aldehydic metal-containing intermediates, the initial anomeric centres become secondary alcohols, and the aglycone of the starting materials are lost during the reaction. The C-5 centre becomes a carbonyl group. Otherwise, titanium, aluminium or Grignard compounds can be used to promote the conversions but, very significantly, in these instances the products retain the C-1 substituents of the starting materials. Also, when triisobutylaluminium is used, the products isolated are the alcohols derived by reduction of the carbonyl groups of the initially formed cyclohexanones. The reactions have been used in the synthesis of a wide range of inositols, their derivatives, and other compounds containing functionalized cyclohexane rings.