OXIDATIVE COUPLING OF THE ENOLATE ANION OF (1R)-(+)-VERBENONE WITH FE(III) AND CU(II) SALTS - 2 MODES OF CONJOINING THIS BICYCLIC KETONE ACROSS A BENZENE

The regioselectivity of the oxidative coupling of the enolate anion of (1R)-(+)-verbenone (97% ee) has been examined with CuCl2 and FeCl3 as catalysts. With Cu(II), selective formation of the gamma,gamma-product is observed. An increase in temperature above -40 degrees C results in further oxidation of the intra-ring ethano bridge to a trans double bond, provided that excess LDA has been added. In the presence of Fe(III), the coupling is partially diverted to the alpha,gamma-product, which has proven amenable to direct conversion to that C-2-symmetric ''dimer'' having the carbonyl groups in a para relationship. The second C-2 ''dimer'' featuring meta orientation of the ketone functionalities has been conveniently prepared from the trienedione or its derived diol by thermal or photochemical trans --> cis equilibration, thermal 6 pi electrocyclization with concurrent aromatization, and PCC oxidation. Some potential applications of this conformationally rigid benzenoid system to enantioselective synthesis are outlined.