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Synlett 1992; 1992(7): 577-578
DOI: 10.1055/s-1992-21421
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Stereocontrolled Radical Mediated Ring-Opening Reactions of Vinylcyclopropanes: Concise Syntheses of Cembrene, Cembrenene, Neocembrene and Isocembrene from Casbene

Gerald Pattenden* , J. Smithies
  • *Department of Chemistry, The University, Nottingham NG7 2RD, England
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Publication Date:
08 March 2002 (online)

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Treatment of casbene 1 with an ethanethio radical results in regioselective 1,4-addition to the vinylcyclopropane moiety in 1, producing the cembrane sulphide 7 in 67-75% yield. Oxidation of 7 to 8, followed by thermolysis then produces isocembrene 9. When casbene 1 was heated for 10 minutes in the presence of N-bromosuccinimide-2,2′-azobisisobutyronitrile it underwent oxidative rearrangement, via the allylic radical 11, to cembrenene 13 (60%). Hydrogenation of cembrenene using Wilkinson's catalyst and palladium on carbon then led to cembrene 14 and neocembrene 15, respectively.

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