Synthesis of Enantiomerically Pure Cyclopropyl Boronic Esters

The synthesis of enantiomerically pure cyclopropyl boronic esters 12a−d and 13a−d has been achieved. The high‐yielding process involves the condensation of readily available alkenyl boronic acids 1a−d with (2 R ,3 R )‐1,4‐dimethoxy‐1,1,4,4‐tetraphenyl‐2,3‐butanediol ( 10 ), Pd(II) acetate catalyzed cyclopropanation with diazomethane, and chromatographic separation of the diastereoisomers. The absolute configuration has been determined by converting 12a−d and 13a−d to the corresponding cyclopropanols (1 R ,2 R )‐ 4a+b /(1 R ,2 S )‐ 4c+d and (1 S ,2 S )‐ 4a+b /(1 S ,2 R )‐ 4c+d , respectively, compounds that allowed correlations to be made with previously published data.