Stereo- and Chemoselective Conversion of Alkynylphosphonates to Vinyl and Alkyl Phosphonates.

A novel strategy for the selective semi-reduction and exhaustive reduction of alkynyl phosphonates to (E)-vinyl phosphonates and alkyl phosphonates, respectively, has been developed using a Zn/NiCl2·6H2O system. The hydrogenation chemoselectivity is effectively tuned by simply switching the reaction solvent from acetonitrile to ethanol. Furthermore, the synthetic utility of this methodology is demonstrated through a late-stage tetradeuteration sequence employing readily available deuterium oxide as the isotope source. This protocol features simple operation and mild conditions, enabling the efficient conversion of readily available alkynyl phosphonates into alkyl and vinyl phosphonate products. Notably, by using D2O as the deuterium source, a range of deuterated alkyl phosphonates were obtained in excellent yields.