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 P-chiral alkynylphosphoryl
compounds via palladium-catalyzed stereoselective cross dehydrogenative
coupling of P-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.