Synthesis of the (4R,5R)-Isomer of 5-Hydroxy-6-phenyl-4-hexanolide, a Lateral Root-inducing Substance Isolated from Erwinia quercina

Lipase-catalyzed enantioselective lactonization of racemic methyl 6-phenyl-4-hydroxy-5-hexynoate worked well to afford (R)-6-phenyl-5-hexyn-4-olide (42% yield, 81% e.e.). The e.e. of the product was enhanced to 97% by the repetition of enzymatic reaction. From this lactone, (4R,5R)-isomer of 5-hydroxy-6-phenyl-4-hexanolide, a lateral root inducing substance from Erwinia quercina was synthesized via a selective epoxidation of the intermediate and subsequent hydrogenolysis as the keystep.