Unexpected solvent-free cycloadditions of 1,3-cyclohexanediones to 1-(pyridin-2-yl)-enones mediated by manganese(III) acetate in a ball mill.

Under solvent-free ball-milling conditions, manganese(III) acetate dihydrate-mediated cycloadditions of 5,5-dimethyl-1,3-cyclohexanedione and 1,3-cyclohexanedione to various 1-(pyridin-2-yl)-enones proceeded efficiently to afford trans-2-acyl-3-aryl/alkyl-2,3,6,7-tetrahydro-4(5H)-benzofuranone derivatives. The cyclization reactions exhibited good to excellent yields, as well as extremely high diastereoselectivity and unexpected regioselectivity. Manganese(III) acetate behaved both as an oxidant and as a Lewis acid.