Mechanistic Studies on the Palladium-Catalyzed Cross Dehydrogenative Coupling of P(O)–H Compounds with Terminal Alkynes: Stereochemistry and Reactive Intermediates

The mechanism of the palladium-catalyzed cross dehydrogenative coupling of P­(O)–H compounds with terminal alkynes was studied. Successive ligand-exchange reactions of Pd­(OAc)₂ with a hydrogen phosphoryl compound and a terminal alkyne take place readily to replace the two acetates on palladium, producing the corresponding (phosphoryl) (alkynyl)palladium complexes, which upon heating decomposed to the corresponding alkynylphosphorus compound. It is also confirmed that in the stoichiometric reactions of the complexes, the configuration at phosphorus is retained. On the basis of these stoichiometric reactions, an efficient synthesis of <i>P</i>-chiral alkynylphosphoryl compounds via palladium-catalyzed stereoselective cross dehydrogenative coupling of <i>P</i>-chiral P­(O)–H compounds with terminal alkynes was developed. The key palladium complexes and the stereochemistry of the chiral phosphorus compounds are all unambiguously determined by single-crystal X-ray analysis