A NEW SYNTHESIS OF SUBSTITUTED FULVENES

A new fulvene synthesis results from the palladium-catalyzed [2 + 2 + 2] annulation of 1 mol of a β-substituted vinyl iodide and 2 mol of a monosubstituted acetylene. This variant of the Heck reaction tolerates a wide range of substrate substituents with the best results obtained by using the catalyst, Pd(CH3CN)2Cl2. Addition of Cu'I to the reaction affords high yields of 1,3-enyne and no fulvene. A [6.5]spiro system is formed from 4-tert-butyl-1-cyclohexenyl triflate and a biphenyl is formed from I-aryl-1-bromoethene under these conditions. A mechanism for this novel fulvene synthesis is proposed. © 1990, American Chemical Society. All rights reserved.