Enantioselective Synthesis of Bicyclo Compounds Catalyzed by Rhodium and Benzoic Acid

Tanaka et al. have reported the synthesis of bicyclo[3.1.0]hexanes by the enantioselective cycloisomerization of 1,6-enynes using rhodium and benzoic acid catalysts. According to their results, the enantioselective cycloisomerization of 1,6-enynes possessing carbonyl groups at the enyne linkage proceeds by using [Rh(cod)₂]BF₄, (S)-Segphos and benzoic acid as catalysts successfully giving 2-alkylidenebicyclo[3.1.0]hexanes. Bicyclo[3.1.0]hexane skeletons are found as core structures of natural products, so this reaction has attracted much attention as a useful synthetic method for these bicyclo compounds. Furthermore, they have also reported the one-pot synthesis of bicyclo lactones by the enantioselective cycloisomerization of 1,6-enynes followed by the tosyl acid-promoted lactonization.