Dual mechanisms of an organocatalytic homodimerization reaction

The l-proline organocatalytic homodimerization of 2-cyclohexenone has been studied and it is concluded that the mechanism of the reaction follows competing pathways involving either a two-step imine/enamine addition or a concerted Diels-Alder cycloaddition where the ultimate product distribution is dependent upon the ratio of the organocatalyst to 2-cyclohexenone and a base present.

An organocatalytic homodimerization reaction is shown to proceed via a cascade mechanism involving enamine-iminium ion intermediates in competition with a concerted Diels-Alder pathway.