Synthesis of Fused Piperidines by Rhodium-Catalyzed Cyclization

Significance

The synthesis of six-membered azacycles by rhodium-catalyzed cycloisomerization of N-propargyl enamine derivatives in yields ranging from 53-99% is reported. The use of base enhances the yields of products. Both endo-diene A and exo-diene B products are formed depending on the nature of R and the product thermodynamic stability. Electron-withdrawing N-acyl groups appear to have minor impact on the yields of pro­ducts. Single diastereomers of products are obtained from substrates bearing a propargylic stereogenic center. Hydrogenation of the non-enamine double bond in the products obtained from monocyclic N-propargyl enamines leads to the basic 1-azabicyclo[4.4.0] and [4.3.0] skeletons.