ENANTIOSELECTIVE SYNTHESIS OF POLYFUNCTIONAL SMALL BUILDING-BLOCKS WITH A QUATERNARY STEREOGENIC CENTER

Application of the SAMP-/RAMP-hydrazone method offers an efficient and flexible access to compounds with a quaternary stereogenic center. Examples bearing silyl, thio, phenyl, aldo, keto, ester, and alkyl functionalities are described. The 2-phenylaldehydes and -ketones and the beta-keto esters 4 were obtained in good overall yields and with variable enantiomeric excesses. The synthesis of the thiolated 2-formyl and 3-formyl carboxylic esters 12 was achieved in high overall carboxylic ester and acids 16 were produced in moderate to high overall yields and with moderate to excellent enantiomeric excesses, depending on the electrophile used for the quaternization. The absolute configurations of the compounds 12 and 16 were determined by X-ray structure analyses, and the mechanism of the quaternization is postulated.