Pd-catalyzed selective tandem arylation–alkylation of 1,1-dihalo-1-alkenes with aryl- and alkylzinc derivatives to produce α-alkyl-substituted styrene derivatives

Trans-selective monoarylation of 1,1-dibromo- and 1,1-dichloro-1-alkenes (1) can be achieved in >80% yields and in ≥98–99% stereoselectivity with arylzinc bromides in the presence of a catalytic amount of Cl2Pd(DPEphos) or Cl2Pd(dppb), the former permitting cleaner and higher yielding reactions. Although THF is a generally satisfactory solvent, ether and toluene are superior to THF in some cases. The second substitution of (Z)-α-bromostyrenes (3) with alkylzincs in the presence of 2 mol% of Pd(tBu3P)2 proceeds to give the corresponding 2 in >90% yields and in ≥98–99% stereoselectivity. Although somewhat less satisfactory, the use of Cl2Pd(DPEphos) permits a one-pot tandem arylation–alkylation.