Homoallylic ketones and pyrroles by way of copper-catalyzed cascade additions of alkyl-substituted vinyl Grignard reagents to esters

Abstract

Exploring the scope of the copper-catalyzed cascade addition of vinyl Grignard reagents to carboxylic esters, a set of substituted homoallylic ketones (γ,δ-unsaturated ketones) have been synthesized in 11%–94% yields from treatment of methyl 4-methoxybenzoate and methyl N-Boc-β-alaninate with different methyl-, dimethyl-, and phenyl-substituted vinyl Grignard reagents in the presence of catalytic amounts of CuCN in THF. The respective 2,4-di-, 2,3,5-tri-, and 2,3,4,5-tetrasubstituted pyrroles were obtained in 47%–93% yields from the homoallylic ketones by a sequence featuring ozonolysis followed by Paal–Knorr condensation with ammonium formate.Key words: copper-catalyzed cascade addition, homoallylic ketone, alkyl-substituted vinyl Grignard reagents, ozonolysis, pyrrole, γ,δ-unsaturated ketone.