Intramolecular ene reactions. Stereo- and enantioselective synthesis of spirolactams through thermolysis of enamino carboxamides

A new and facile access to spirolactams based on the thermal rearrangement of tertiary and secondary enamino carboxamides has been developed. The enamine group of an enamino carboxamide, in which no electron-withdrawing group is present in the enophile, can be involved in the ene reaction and the enamino carboxamide can be transformed into enamino or imino spirolactams. In the case of secondary carboxamido enamines, the diastereoselectivity is higher than 98%. If chiral nonracemic analogs are utilized, 50-54% enantiomeric excesses can be achieved in the final products.