Rh-catalyzed addition of β-carbonyl pinacol alkylboronates to aldehydes: asymmetric synthesis of γ-butyrolactones.

The rhodium-catalyzed 1,2-addition of chiral benzylic secondary alkylboronic esters with a coordinating carbonyl group to aldehydes was demonstrated with high levels of enantiospecificity. Pinacol boronic ester derivatives can be employed directly for the addition in the presence of KHF2 without the use of corresponding trifluoroborate salts where retention of the configuration was observed. Enantiomerically enriched β,γ-diaryl-substituted γ-butyrolactones were synthesized in good yields.