Iridium-Catalyzed Hydrohydroxyalkylation of Butadiene: Carbonyl Crotylation

Exposure of alcohols 1a-1i to butadiene in the presence of a cyclometallated iridium catalyst derived from allyl acetate, 4-methoxy-3-nitrobenzoic acid and 2,2'-bis(diphenylphosphino) biphenyl (BIPHEP) results in hydrogen transfer to generate aldehyde-allyliridium pairs, which engage in C-C coupling to form products of carbonyl crotylation. Under related conditions using 1,4-butanediol as hydrogen donor, butadiene reductively couples to aldehydes 2e-2g and 2i to furnish carbonyl crotylation products 3e-3g and 3i. Thus, butadiene-mediated carbonyl crotylation occurs with equal facility from the alcohol or aldehyde oxidation level with complete levels of branched regioselectivity.