can undergo a thermal ring contraction after an in situ triflation. High yields of ring-contraction products are obtained with DBU when the migrating carbon is a methylene, while best results are obtained with Et3N for the migration of quaternary carbons. In some cases, the regiochemical outcome of the reaction can be controlled by changing the base. This novel thermalrearrangement complements a similar
Photochemical Rearrangement of <i>N</i>-Chlorolactams: A Route to <i>N</i>-Heterocycles through Concerted Ring Contraction
作者:Dana K. Winter、Alexandre Drouin、Jean Lessard、Claude Spino
DOI:10.1021/jo100181h
日期:2010.4.16
We report a novel ringcontraction allowing the direct conversion of N-chlorolactams to their corresponding ring-contraction N-heterocycles upon photolysis. Results show that the rearrangement occurs with a variety of N-chlorolactams and that the greater the substitution at the migrating carbon, the greater the yield of product. Importantly, stereochemistry at the migrating carbon is conserved in the
[Bis(trifluoroacetoxy)iodo]p-nitrobenzene and [Bis(trifluoroacetoxy)iodo]pentafluorobenzene as Lead Reagents for the Direct Ring Contraction of Lactams to Pyrrolidines