title: Regioselective 1,4-Conjugate Addition of Grignard Reagents to α,β-γ,δ-Dienones and α,β-γ,δ-Dienyl Thiol Esters.
abstract: Alkyl Grignard reagents (Et,nBu,iPr, cyclohexyl), with the exception oftBuMgCl, undergo exclusive or exceptionally highly regioselective 1,4-addition reactions to α,β-γ,δ-unsaturated ketones, while aryl and heteroaryl Grignard reagents give mixed results ranging from exclusive 1,4-addition (1-naphthyl, 2-N-methylpyrrolyl) to regioselective 1,2-addition (2-furyl, 2:1). All alkyl, aryl, and heteroaryl Grignard reagents examined gave exclusive 1,4-addition reactions with α,β-γ,δ-unsaturated thiol esters, with the exception oftBuMgCl, which gave an 80:20 mixture of 1,4:1,6-addition products. The high chemo- and regioselectivity observed for these reactions is attributed to a radical or radical-like pathway for the alkyl Grignard reagents and possibly a carbanion pathway for aryl Grignard reagents. The α,γ-dienyl thiol esters provide for a one-pot tandem 1,4-addition-nucleophilic acyl substitution reaction sequence to afford 3-substituted 4-enone moieties.
authors.affiliation: Hunter Laboratory, Department of Chemistry, Clemson University , Clemson, South Carolina 29634-0973, United States.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Amoah
authors.affiliation: Hunter Laboratory, Department of Chemistry, Clemson University , Clemson, South Carolina 29634-0973, United States.
authors.forename: R Karl
authors.identifier: 0000-0002-9166-8895
authors.initials: RK
authors.lastname: Dieter