Stereoselective Homoallylation of Aldehydes and Ketones

Significance

In the presence of catalytic Ni(acac)₂ and stoichiometric Et₃B or Et₂Zn, 1,3-dienes are added to aldehydes and ketones to stereoselectively afford homoallylation products. Aromatic aldehydes react in the presence of Et₃B with 1,3-anti selectivity whereas aliphatic aldehydes react in the presence of Et₂Zn to give exclusively 1,3-anti products. Terminally substituted dienes generally afford 1,2-anti products, except hydroxyterminal dienes which afford 1,2-syn products. Less reactive moieties such as ketones and cyclohexadiene required Et₂Zn, and afforded the product in moderate yields, with cyclohexadiene affording allylation, not homallylation products. Catalyst loadings as low as 1 mol% were used on a 50-mmol scale and the diene loading was decreased to 1.1 equivalents. The method was applied to a 10-g scale reaction of isoprene and dehydrocinnamaldehyde, affording product in 80% yield.