Formal cycloaddition reactions of vinylogous amides with alpha,beta-unsaturated iminiums. A strategy for constructing piperidinyl heterocycles

A formal [3 + 3] cycloaddition strategy for constructing piperidinyl hetero cycles from vinylogous amides and alpha,beta-unsaturated iminiums is descri bed here, These reactions proceed well, leading to various heterocycles tha t could serve as useful synthetic building blocks. Comparative studies betw een the reactivities of vinylogous amides and other 1,3-diketo systems have also been examined. Preferences for the nitrogen atom during the electrocy clic ring closure step are noted in these reactions, and preliminary calcul ations suggest that these preferences could result from electronic factors.