TOTAL SYNTHESIS OF (+ -)-SILPHINENE - NON PHOTOCHEMICAL CYCLOBUTENIC ROUTE TO A CRUCIAL INTERMEDIATE/

The cyclobutenic ester 1, readily available by thermal [2+2] cycloaddi tion of the silyl enol ether derived from cyclopentanone with ethyl pr opynoate, is easily transformed into the diquinanic alcohol 3 via the bicycle [2.1.0] pentane intermediate 2. After protection as the thexyl dimethylsilyl ether, an allylic oxidation stereospecifically introduce s a hydroxyl group at position 8. Following formation of the benzyl et her, the diquinane 9 was then transformed in four steps into the triqu inane 20 using a silyl-assisted Nazarov type cyclisation. From this in termediate, (+/-)-silphinene has previously been synthesized. (C) 1997 , Elsevier Science Ltd.