Electrophilic activation of lactams with Tf2O and pyridine: expedient synthesis of (+/-)-tetraponerine T4.

[reaction: see text] The electrophilic activation of lactams with triflic anhydride in the presence of pyridine was investigated by NMR. It was found that 2-pyrrolidone led to the clean formation of the corresponding pyridinium imidate in 89% isolated yield. The subsequent nucleophilic addition of organometallic reagents led to 2-substituted dihydropyridines. A synthesis of (+/-)-tetraponerine T4 with three simple building blocks was accomplished in 3 steps (38% yield).