Regioselective Photochemical Rearrangement of N-Mesyloxylactams

A Photorearrangement To Construct the ABDE Tetracyclic Core of Palau'amine

A synthesis of the ABDE tetracyclic carbon core of palau'amine was achieved in 9 steps from commercial materials. The core's most notable feature, a highly strained trans cyclopenta[ c]pyrrolidine, was obtained in high yield using a ring contraction strategy starting from a much less strained trans bicyclic lactam derivative that is accessible in only 7 steps.

Converting cycloalkanones into N-heterocycles: formal synthesis of (-)-gephyrotoxin 287C

The photochemical rearrangement of N-activated lactams enables their ring contraction concomitant with the migration of a carbon onto a nitrogen atom. When coupled with the Beckmann rearrangement, this photochemical ring contraction converts cycloalkanones into N-heterocycles in a few steps and in a stereospecific manner. To showcase the method, we performed an efficient formal synthesis of (-)-gephyrotoxin 287C.

Photochemical and thermal ring-contraction of cyclic hydroxamic acid derivatives

Cyclic hydroxamic acids 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 Et(3)N for the migration of quaternary carbons. In some cases, the regiochemical outcome of the reaction can be controlled by changing the base. This novel thermal rearrangement complements a similar but photochemical rearrangement of N-mesyloxylactams.