Enantioselective synthesis of cyclohexene nitro aldehydes via Diels–Alder reactions with sugar nitroolefins

Abstract

Uncatalysed Diets-Alder reactions between (E)-1-deoxy-1-nitroalkenes derived from sugars and 2,3-dimethylbuta-1,3-diene yielded an easily separable mixture of the two possible diastereoisomeric adducts, with good diastereofacial selectivity. In each case, preponderance of the major adduct has been rationalized in terms of the configuration of the chiral centre adjacent to the dienophilic double bond. Acid or alkaline deacetylation of the adducts, followed by degradative oxidation of the sugar side-chains, led to enantiomerically pure trans- or cis-cyclohexene nitro aldehydes. We also report on the easy elimination of the nitro group in nitro aldehydes, leading to cyclohexa-1,4-diene 11 or the aromatic aldehyde 12.