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Abstract

Enamines of cyclodecanone and cyclododecanone (1a-d) react with dimethyl acetylenedicarboxylate (DMAD) in an apolar solvent via (2 + 2) cycloaddition and conrotatory opening of the cyclobutene ring in 3 to give the cis,trans-cycloalkadienes 5a-d in yields of 44–85%. The compounds 5 do not undergo further thermal or photochemical transformation of the cis,trans moiety. In methanol, the enamines react with DMAD to give bicyclo[7.2.1]dodecene (8a) or bicyclo[9.2.1]tetradecene (8b and 8c) derivatives. These reactions take place via intramolecular nucleophilic addition of the enamine moiety to the α-methoxycarbonyl group in 10, which is formed from the intermediate Michael adduct 9. The structure of 8b was determined by single-crystal X-ray analysis.