P-Chirogenic silylphosphine-boranes: synthesis and phospha-Michael reactions

Chiral and achiral silylphosphine-boranes were prepared in high yields by reaction of phosphide boranes with halogenosilanes. Their reaction at room temperature with Michael acceptors afforded 1,4-addition products as silylenol ether or ketone derivatives in good to excellent yields. In the case of the 2,3-dihalogeno-maleimides, the double addition of silylphosphine-borane led to the corresponding trans-diphosphine-boranes in 86% yield. Noteworthy, the reaction of P-chirogenic silylphosphine-boranes with enones afforded the phospha-Michael adducts without racemization at the P-center. While the silylphosphine-boranes have been scarcely described so far, these compounds demonstrate their great interest for the synthesis of chiral and achiral functionalized organophosphorus compounds.