Enzyme-promoted desymmetrization of bis(2-hydroxymethylphenyl) sulfoxide as a route to tridentate chiral catalysts

The desymmetrization of prochiral bis(2-hydroxymethylphenyl) sulfoxide 3 was efficiently performed via acetylation promoted by commonly available lipases. Two lipases, namely, CAL-B and LPL proved particularly efficient to give 2-acetoxymethylphenyl 2-hydroxymethylphenyl sulfoxide 4 in up to 98% yield and with up to 98% ee. On the basis of an X-ray analysis, the absolute configuration of 4 was determined as (+)-(R). The enantiomerically pure product 4 was then transformed into a series of enantiomerically pure diastereomeric 2-aminomethylphenyl 2-hydroxymethylphenyl sulfoxides 8 in which the amino groups originated from enantiomerically pure amines having additional C-stereogenic centres. Compounds 8 were examined as possible tridentate chiral catalysts in a reference reaction of diethylzinc with benzaldehyde to give the expected product, 1-phenylpropan-1-ol, in moderate yields and with ee’s of up to 50%.