The synthesis of strained bridgehead olefins by the intramolecular wittig reaction

Abstract

Bicyclo[4.2.llnon-l(8)-ene 1 has been synthesized previously in low yield together with its l(2)-isomer 2 from the corresponding bridgehead ammonium 3 hydroxide by pyrolysis and preparative vapor phase chromatography . The synthesis by the intramolecular Wittig reaction, however, is straightforward and gives the pure olefin 1 in 57 % yield. The use of a keto phosphonium salt as a precursor was developed in our laboratory 4 and successfully applied to the synthesis of bicyclo[3.3.l]non-1-ene 2 . Recently the preparation of the unstable bicyclo[3.2.l]oct-l(7)-ene 4 and the attempted formation of ene 5 by the same method was reported by Dauben and Robbins bicyclo[2.2.l]hept-l5 .