Influence of aluminum Lewis acids on the diastereoselectivity of the nickel-catalyzed [2+2+2] cycloaddition of norbornadiene and electron deficient alkenes

The stereoselective formation of 8-substituted deltacyclanes by homo Diels–Alder (HDA) reaction using a phosphine modified nickel catalyst generated by reduction of Ni(acac)2 with alkylaluminums is discussed. Depending on the nature of the alkene and on the nickel catalytic system, fair to excellent exo selectivity are observed. A switch in selectivity favoring the endo-cycloadduct is observed when the polar methoxycarbonyl group substituted alkene is activated with aluminum species.