Sequence of intramolecular carbonylation and asymmetric hydrogenation reactions: highly regio- and enantioselective synthesis of medium ring tricyclic lactams

The intramolecular cyclocarbonylation reaction with palladium-complexed dendrimers on silica is a very effective method for the regioselective synthesis of methylene 8-, 9-, and 10-membered rings. The heterogeneous dendritic catalysts are easily recovered by simple filtration and reused for up to 10 cycles with only a slight loss of activity. Asymmetric hydrogenation of the resulting unsaturated heterocycles affords optically active tricyclic lactams in excellent yields and in high enantiomeric excess. This process can tolerate a wide array of functional groups, including halide, ether, nitrile, ketone, and ester. Moreover, the variation of heteroatom on the rings does not have any influence on the efficiency and enantioselectivity of the reaction.