Total Syntheses of (−)- and (+)-Boronolide and Their Plant Growth-Inhibitory Activity

Abstract

Optically pure (+)- and (−)-boronolides were stereoselectively synthesized from yeast reductive products which had been obtained by yeast reduction of one common racemic substrate. The lactone structure of boronolide was constructed by Baeyer-Villiger oxidation. The stereochemistry of the yeast reduction products was studied to obtain the stereocenters at 5 positions of the dodecanolides of (+)- and (−)-boronolides. The stereochemistry of the 6 and 7 positions was obtained by AD-mix-α or β oxidation. The chiral center at the 8 position was constructed by employing (R)-(+)- or (S)-(−)-2-methyl-CBS-oxazaborolidine reduction or the Mitsunobu reaction. The plant growth-inhibitory activity against Echinochloa crusgalli L. of naturally occurring (+)-boronolide was higher than that of the (−)-boronolide.