Formation of Spirocyclic Compounds from Heck Cyclizations Invoking Cyclic Enamides

The palladium-mediated transformation of 3,4-dihydro-2(1H)-pyridinones 12 featuring a (2-bromophenyl)ethyl substituent in the 5-position produces spirocyclic products, imides 14 and amides 15. The formation of these products can be explained by insertion of the enamide double bond into the initial aryl-Pd bond followed by oxidation or reduction of the organopalladium intermediate. Alternatively, formation of these spiro compounds might proceed via acyliminium ion intermediates.