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In the presence of titanium(IV) tetraethoxide ((EtO) 4 Ti), menthyl arylglyoxylates are prepared by transesterification of ethyl arylglyoxylates and natural (À)-(1R,2S,5R)-menthol. Using menthyl as a chiral auxiliary, the corresponding novel (R)-menthyl 2-aryl-2-hydroxybutanoates are synthesized by the addition of Et 2 Zn with menthyl arylglyoxylates. The structures of the products are characterized by IR and 1 H-and 13 C-NMR spectroscopy, mass spectrometry, and elemental analysis. The diastereoselectivities are analyzed by HPLC. The addition reactions are completed with good yields and high diastereoisomeric excess (de up to 95%), and, after hydrolysis, the (R)-2-aryl-2-hydroxybutanoic acids are obtained with high optical purities.Introduction. -The synthesis of chiral a-hydroxy compounds by the asymmetric addition of organometallics to aldehydes and ketones have extensively been reported [1]. We anticipate that a-keto esters will display a reactive intermediate similar to that of aldehydes and ketones [2]. Furthermore, the resultant a-alkyl-a-hydroxy esters are amenable to derivatization and useful starting components for the synthesis of pharmaceutical agents and natural products [3]. Diastereoselective addition of organometallic reagents to a-keto esters by means of a chiral auxiliary is a methodology to obtain chiral tertiary a-hydroxy carboxylic acids. Among various chiral auxiliaries employed for the stereoselective synthesis of tertiary alcohols, molecules based on a cyclohexane frame such as menthol (¼ 5-methyl-2-(1-methylethyl)cyclohexanol) are powerful, because they provide a higher asymmetric effect, and they are readily accessible natural products. Using menthol as the chiral auxiliary provides many advantages such as low cost, availability, good selectivity, and a tendency of intermediates to be crystalline [4].Here, we present a novel stereoselective synthesis of tertiary a-hydroxy carboxylic acids. First, ethyl arylglyoxylates (¼ 2-aryl-2-oxoacetates) were synthesized as described in the literature [5] [6]. Subsequently, the (À)-menthyl (¼ 5-methyl-2-(1-methylethyl)cyclohex-1-yl) arylglyoxylates were prepared by transesterification conditions with a catalyst of (EtO) 4 Ti. Finally, the diastereoselective addition to (À)-menthyl aketo esters employed organozinc or Grignard reagents to afford the a-hydroxy esters. The esters were saponified to afford the chiral tertiary a-hydroxy carboxylic acids. The synthetic route is illustrated in Scheme 1.

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