Iridium complex-catalyzed allylic alkylation

An iridium complex was found to be an efficient catalyst for allylic alkylation of allylic acetates with a stabilized carbon nucleophile. Two unique features of iridium complex catalysis are found. (1) Regioselective alkylation at the substituted allylic terminus: the reaction of (E)-2-alkenyl acetates or 1-substituted 2-propenyl acetates with sodium salt of diethyl malonate in the presence of a catalytic amount of [Ir(COD)Cl](2)/P(OPh)(3) (P/Ir = 1-2) gave products alkylated at the substituted allylic terminus with 95-99% selectivities. P-31 NMR and C-13 NMR revealed that a catalytically active species is Ir(COD) (P(OPh)(3))Cl. The pi-acceptor property of P(OPh)(3) promotes a carbonium ion character at the substituted allylic terminus. Therefore, the nucleophile is directed to this position. (2) Retention of Z geometry in the allylic alkylation of (Z) -2-alkenyl acetates; the reaction of (Z)-2-alkenyl acetates gave a product alkylated at the unsubstituted allylic terminus with the retention of Z geometry predominantly. Retention of Z geometry in allylic alkylation is also possible by iridium catalysis. (C) 2000 Elsevier Science Ltd All rights reserved.