On the Mechanism of Carbohydroxypalladation of Enynes. Additional Insights on the Cyclization of Enynes with Electrophilic Metal Complexes

Different mechanisms have been proposed for the cyclization of enynes catalyzed by electrophilic metal halides or complexes. We present evidence to indicate that the previously reported “carbohydroxypalladation” and the “hydroxycyclization catalyzed by Pt II ” are closely related reactions. Thus, palladium complexes formed in situ from PdCl 2 and trisulfonated phosphane TPPTS or cyclic phosphite P(OCH 2 ) 3 CEt as the ligands catalyze the methoxy‐ or hydroxycyclization of enynes with selectivities similar to those observed with Pt II complexes. Deuteration studies indicate that activation of the alkyne by Pd II promotes an anti‐addition of the alkene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)