Synthesis of chiral cyclic α-p-tolylsulphinyl ketones

Abstract

Two new syntheses of optically pure cyclic β-oxo sulphoxides are described. Reactions of (–)menthyl toluene-p-sulphinate with cycloalkanones (CH₂)_nCO (n= 4, 5, and 6) and PrⁱNMgBr yield mixtures of diastereoisomeric sulphoxides without epimerization at sulphur. With the cyclopentanone (n= 4) yields are poor owing to competitive autocondensation of the keeone. Reactions of cycloalkanone N-phenylimines with the sulphinate in the presence of lithium di-isopropylamide afford, after chromatographic purification, the same mixtures of diastereoisomeric β-oxo sulphoxides with no aldolic condensation product.