Rhodium-Catalyzed Asymmetric Cycloisomerization of 1,6-Enynes

Significance

1,6-Enynes can be converted into bicyclo[4.1.0]heptene derivatives via 6-endo-dig cycloisomerization catalyzed by π-acidic metals. Despite the high synthetic utility of this transformation, there have been only few asymmetric variants reported so far. In this paper the authors describe a rhodium-catalyzed cycloisomerization of oxygen- and nitrogen-bridged 1,6-enynes proceeding with high yields (71-94%) and enantio­selectivities (68-99% ee). Substituted tetrafluoro­benzobarrelene (TFB, 1) was found to be the optimum ligand showing high catalytic activity presumably due to its high π-accepting ability. It can be expected that the unique catalyst design will be suitable for other applications of transition-metal catalysis.