Nickel-catalyzed intramolecular homoallylation of omega-dienyl aldehyde.

[reaction: see text] In the presence of a catalytic amount of Ni(acac)(2), Et(3)B and Et(2)Zn nicely promote a reductive homoallylic cyclization of omega-dienyl aldehydes and provide 2-allylcyclopentanols and -cyclohexanols with high stereoselectivity in excellent yield. The reaction requires only two kinds of commercially available, inexpensive reagents, Ni(acac)(2) and Et(2)Zn or Et(3)B, and completes at room temperature within 30 min with Et(2)Zn and 1-2 days with Et(3)B. No ligand additives (e.g., phosphine, nitrogen compounds) are required.