Nitrous acid elimination from 4-alkyl-5-formyl-4-nitrocyclohex-1-enes: synthesis of mono and bicyclic benzene and dihydrobenzene derivatives

Elimination of nitrous acid from 4-alkyl-5-formyl-4-nitrocyclohex-1-enes, b y treatment with silica gel or potassium carbonate, is described. Whereas i n the former case the product consisted in a mixture of the starting materi al, 2-alkyl-4,5dimethylcyclohexa-1,4-diene-1-carbaldehyde and 2-alkyl-4,5-d imethylbenzaldehyde, reaction with potassium carbonate at 60 degreesC yield ed exclusively aromatic compounds. Furthermore, when a ketone Function was present in the gamma -position of the ail;yl chain at C-4, the alkaline med ium promoted an intramolecular. aldol condensation, bring obtained bicyclic products. PM3 calculations have been made to justify the result of the cyc lization. (C) 2001 Elsevier Science Ltd. All rights reserved.