[2+2] cycloadditions of electron-poor acetylenes to endocyclic enaminones : ring expansion reactions

Reactions of cyclic enaminones, derived from cyclic five- and six-membered 1,3-diones, and dimethyl acetylenedicarboxylate (DMAD) under microwave irradiation produced a mixture of two products: ring-expansion products as a result of a [2+2] cycloaddition and Michael adducts. Reaction between 4-(dimethylamino)-2H-chromen-2-one and DMAD leads to three products: 2-(4-(dimethylamino)-2-oxo-2H-chromen-3-yl)maleate as a Michael adduct, dimethyl 1-(dimethylamino)naphthalene-2,3-dicarboxylate as the product of the [2+2] cycloaddition followed by 6π disrotatory electrocyclization and elimination of CO₂ and 4-(dimethylamino)naphthalene-1,2-dicarboxylate as the product of the [4+2] cycloaddition followed by elimination of CO₂.

Read article: Tetrahedron, 2015, 71, 7209-7215.