Lipase-catalyzed kinetic resolution of β-borylated carboxylic esters

The kinetic resolution of chiral β-borylated carboxylic esters via lipase-catalyzed hydrolysis and transesterification reactions was studied. The enantioselective hydrolysis catalyzed by CAL-B furnished the β-borylated carboxylic acid with reasonable enantiomeric excess (62% ee), while both methyl and ethyl β-borylated carboxylic esters were recovered with excellent ee (>99%). Meanwhile, the transesterification reaction of β-borylated carboxylic esters and several alcohols, catalyzed by CAL-B, only indicated a high selectivity when ethanol and methyl-(β-pinacolylboronate)-butanoate were used as substrates, which gave ethyl-(β-pinacolylboronate)-butanoate with >99% ee.

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(S)-Methyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)butanoateC11H21BO4ee >99%[α]D24=+5.5 (c 1.0, CHCl3)Absolute configuration: (S)

(S)-Methyl 3-hydroxybutanoateC5H10O3ee >99%[α]D24=+19.2 (c 1.0, CHCl3)Absolute configuration: (S)

(S)-Ethyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)butanoateC12H23BO4ee >99%[α]D24=+2.1 (c 0.5, CHCl3)Absolute configuration: (S)