Condensed cyclic and bridged-ring systems. Part 13. Synthesis of the insect attractant hydrocarbon, 9a-carbamorphinan, and X-ray structural analyses of 9a-carbamorphinan-10-one and 9a-carba-14α-morphinan-10-one

Abstract

The insect attractant bridged hydrocarbon, (±)-9a-carbamorphinan (1) and its inactive epimer, (±)-9a-carba-14α -morphinan (2), have been synthesized through (±)-9a-carbamorphinan-10-one (3), and (±)-9a-carba-14α-morphinan-10-one (4), prepared by polyphosphoric acid-catalysed cyclization of the double-bond isomeric benzyloctalins (7), derived from Huang-Minlon reduction of 1-benzyl-4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one (6), followed by the benzylic oxidation with chromic acid. The reduction of the easily accessible (±)-9a-carbamorphinan-16-one (10), the orthophosphoric acid-induced cyclization product of (6), provides an efficient alternative route to (1). The structures of the epimeric ketones (3) and (4) have been established by X-ray analysis.