Rhodium-Catalyzed Asymmetric Dehydrocoupling: Enantioselective Synthesis of a P-Stereogenic Diphospholane with Mistake-Correcting Diastereoselectivity

Abstract

Catalytic asymmetric dehydrocoupling of secondary phosphines is a potentially valuable route to enantiomerically enriched P-stereogenic diphosphines for use as ligands or building blocks for chiral bis(phosphines). Rh(diphos*) catalyst precursors converted a rac/ meso mixture of PhHP(CH 2 ) 3 PHPh (1) to the C 2 -symmetric Pstereogenic anti-diphospholane PhP(CH 2 ) 3 PPh (2) in up to a 58:42 enantiomeric ratio (er) with complete diastereoselectivity via catalystmediated isomerization of the intermediate syn-diphospholane 3 to 2 (mistake correction by conversion of the diastereomer meso-3 to chiral C 2 -2). NMR studies of catalytic reactions identified the resting state Rh((R,R)-i-Pr-DuPhos)(PhHP(CH 2 ) 3 PPh) (4) and suggested a proposed mechanism for stereocontrolled P−P bond formation via oxidative addition and reductive elimination steps.