Studies on [PdH]- and [PdCl]-catalyzed intramolecular cyclization: The search for a better solution to selective enyne coupling

On the basis of the hydropalladation and chloropalladation of the carbon-carbon triple bond, [PdH] and [PdCl] active species were employed to catalyze the cyclization of homoallylic 2-alkynoates and omega-alken-2-ynoates. From homoallylic alkynoates, two kinds of alpha-alkylidene-delta-valerolactone derivatives showing different stereochemistries of the exocyclic alkylidene double bond were obtained using two catalytic systems, while from the latter, hydropalladation and chloropalladation showed opposite regioselectivity, giving bis(alkylidene)cycloalkane and cycloalkene derivatives, respectively.