Preparation of enantiomerically pure 4-alkyl-5-formyl-4-nitrocyclohex-1-enes from 5-glyco-4-nitrocyclohex-1-enes

Base-catalyzed (TMG, DBU or TEA) asymmetric Michael reactions between 5-glyco-4-nitrocyclohex-1-enes 1a or 1b and a number of mono- or alpha,beta-disubstituted electron-deficient alkenes yielded, in all cases, adducts in which the sugar side-chain and the added group on C-4 of the cyclohexene ring showed a trans-relationship. Furthermore, some of the adducts have been used to prepare enantiomerically pure 4-alkyl-5-formyl-4-nitrocyclohex-1-enes by a two-step process involving base-catalyzed (NaOMe) deacetylation of their respective sugar side-chains and subsequent oxidative cleavage (NaIO4). When reactions of la or 1b with dimethyl maleate, dimethyl fumarate or methyl trans-4-oxopentenoate were carried out with DBU (instead of TMG) as catalyst, there was in situ elimination of nitrous acid. (C) 2002 Elsevier Science Ltd. All rights reserved.