Stereocontrolled synthesis and cyclization of (+,−)-α,α’-dihydroxy-α,α ’, β-trimethylglutaric acid derivatives

Hydrocyanation of 3-methylpentane-2,4-dione stereospecifically gave trans,trans-iminolactone 1, whose configuration was established by X-ray diffraction of the corresponding lactone 2; the rate of cyclization of the diastereoisomeric lactonic acids 3a,b and their esters 4a,b into dilactone 5 was controlled sterically by the methyl groups with cis,cis-isomers 3b, 4b predominating; alcoholysis of 5 regiospecifically afforded ester 4b.