Asymmetric Cu(I)-Catalyzed Conjugate Borylation of α,β-Unsaturated Acyl Silanes

We report the development of a Cu(I)-catalyzed conjugate borylation of alpha,beta-unsaturated acyl silanes using bis(pinacoloto)diboron. Racemic borylations of beta -aryl-and beta-alkyl-substituted silyl enones were achieved using ligand-free conditions to access beta-borylated acyl silanes in up to 97% yield. Josiphos enabled the synthesis of enantioenriched boronic esters in up to 58% yield and 94% ee. The racemic reaction was demonstrated on 5.0 mmol scale and isolation of the boronic esters was achieved using simple filtration and normal-phase chromatography. This work supplements known methods to access boronic esters from electron-deficient olefins using Cu(I) catalysis.

Automated summary

In this study, a Cu(I)-catalyzed conjugate borylation of alpha,beta-unsaturated acyl silanes using bis(pinacoloto)diboron was developed. The racemic borylations of beta -aryl-and beta-alkyl-substituted silyl enones were successfully achieved under ligand-free conditions, leading to the synthesis of beta-borylated acyl silanes with high yields. Furthermore, the introduction of Josiphos catalyst enabled the synthesis of enantioenriched boronic esters with improved yields and enantioselectivity. This work demonstrates the scalability of the reaction and shows the ease of isolating the boronic esters using simple separation techniques.