Tandem Favorskii Intermediate/Cyclization Leading to Tricyclo[4.4.0.0]decanediones

Abstract

The mechanism of dehydrobromination of the bromodiketone 8 leading to the unusual ring system of tricyclo[4.4.0.0]decanediones (9 and 10) is described. An entry into the ring system of the sesquiterpenoid hydrocarbons copaene and ylangene, 8 to 9, is achieved in three steps starting with enone 6. Compound 9 was either derived from a direct internal S_N2 cyclization of 8 or the Favorskii intermediate 8a. Formation of compound 10, on the other hand, can only occur via the Favorskii intermediate 8a. Structure assignments of 9 and 10 were determined using both one‐ and two‐dimensional NMR experiments.

Keywords:

• Copaene
• Favorskii intermediate
• Ylangene

Acknowledgment

We thank D. Locke of Queens College and Cliff Soll from Hunter College for the GC/MS analysis. Special thanks go to William. F. Berkowitz and Robert Bittman of Queens College for many helpful discussions and the Research Foundation of the City University of New York for financial support.