Asymmetric synthesis of benzilic acid analogues using 8-phenylmenthol as a chiral auxiliary

Article abstract of DOI:10.1016/S0957-4166(00)80069-5

Our program on the synthesis of ¹⁸F-labeled muscarinic receptor ligands required the preparation of chiral fluoroalkyl benzilic acids. An enantioselective synthesis of substituted benzilic acids was achieved using 8-phenylmenthol as the chiral auxiliary. Grignard addition to the si face of 8-phenylmenthyl benzoylformate 7 proceeded with high selectivity. The results of the chiral induction support assignments of the chirality of benzilic acids previously resolved by crystallization. The method was used to synthesize (R)-quinuclidinyl-(R)-4-iodo)benzilate, which proved identical to an authentic sample. In addition, the method allows the preparation of (R)- and (S)-fluoroethyl benzilic acids in a stereoselective manner.