Enantioselective synthesis of P-stereogenic allenylphosphines through Ni-catalysed propargylic substitution

Typical methods for the synthesis of P-stereogenic allenylphosphine derivatives depend on chirality transfer from P-stereogenic substrates and require multiple synthetic steps. Now we report a Ni-catalysed enantioselective propargylic substitution reaction for the synthesis of P-stereogenic allenylphosphine derivatives from propargylic carbonates and secondary phosphines. Using in situ generated secondary phosphines, after a reduction of the corresponding phosphine oxides, a wide range of allenylphosphine derivatives with a P-stereogenic centre were synthesized with a high enantiocontrol (up to 97% e.e.). The method was also applied to the enantioconvergent synthesis of the P,axial-stereogenic 1,3-disubstituted allenylphosphines, using secondary propargylic carbonates as substrates with excellent enantio- and diastereocontrol (up to 97% e.e. and 14:1 d.r.) without the need for racemization or symmetrization of the secondary propargylic carbonates. The chiral phosphine products were readily incorporated into transition metal complexes with retention of stereopurity. Experimental and computational mechanistic studies suggest that the process proceeds through an enantioconvergent reaction mechanism, which gives enantioenriched phosphine products from a racemic mixture of secondary propargylic carbonates. The synthesis of P-stereogenic allenylphosphine derivatives is often long or requires preformed P-stereogenic substrates. Now, a one-step enantioconvergent synthesis of allenylphosphines with both P and axial chirality is reported. The process proceeds through a NiII-catalysed propargylic substitution of secondary phosphines, without racemization or symmetrization of the racemic propargylic carbonates, to give P-stereogenic allenylphosphines.