Aza-Baylis−Hillman Reactions of <i>N</i>-Tosylated Aldimines with Activated Allenes and Alkynes in the Presence of Various Lewis Base Promoters

The attempted aza-Baylis−Hillman reactions of N-tosylated aldimines with ethyl 2,3-butadienoate, ethyl penta-2,3-dienoate, penta-3,4-dien-2-one, methyl propiolate, and but-3-yn-2-one have been systematically investigated in the presence of various nitrogen or phosphine Lewis base promoters. We found that a series of nitrogen-containing heterocyclic compounds, as “abnormal” aza-Baylis−Hillman reaction products, can be formed in the presence of an appropriate Lewis base promoter. The Lewis base and solvent effects in these reactions have been discussed along with the corresponding plausible mechanism.