Reaction of alkyl diazoacetate with an olefin catalyzed by a chiral copper complex gives an optically active alkyl cyclopropanecarboxylate. This chiral copper carbenoid reaction was successfully applied to the synthesis of industrially valuable cyclopropanecarboxylic acids: (÷)-trans-chrysanthem ic acid, (÷)-cis-permethrinic acid and (+)-2,2-dimethylcyclopropanecarboxylic acid. A series of effective catalysts, chiral Schiff base-copper complexes, was prepared starting with an optically active a-amino acid to achieve more than 90% e.e. of the products. The chirality of the products was correlated with that of the catalyst on the basis of metallacyclobutane intermediates. CHIRAL COPPER CARBENOID REACTION (ref. 1) AND ITS APPLICATION TO CHRYSANTHEMIC ACID SYNTHESISIn 1966, the first example of asymmetric catalysis (ref. 2) by means of a soluble transition metal complex was reported by Prof. Nozaki and his coworkers. They decomposed ethyl diazoacetate in styrene in the presence of chiral copper complex (1) as a catalyst to give the products, trans-and cis-2-phenyl-cyclopropanecarboxylate (3 and 4), both in an optically active form (Eq 1). This finding demonstrated that the carbene derived from ethyl diazoacetate is not free but is combined with the chiral copper complex to form a carbene-copper complex (ref. 3), which is responsible for the asymmetric induction. Furthermore, the reaction provided a new method for the preparation of optically active cyclopropane derivatives of practical value, although the enantiomeric excess (e.e.) attained at that time was less than 10%.

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We investigated the separation of chrysanthemate isomers (1), particularly the (1R)-trans form, by high-performance liquid chromatography (HPLC) using polysaccharide derivatives, such as the phenylcarbamates and benzoates of cellulose and amylose, as the chiral stationary phases (CSPs). The chiral packing materials (CPMs) having a high chiral recognition for the chrysanthemic acid ethyl ester (1a) were prepared by coating cellulose tris(4-methylbenzoate) (2a) dissolved in solvents containing methyl benzoate or acetophenone as an additive on silica gel. The separation factor for 1a significantly depended on the preparation conditions of CPM 2a, such as the coating amount of 2a and the type and amount of additives. The chiral recognition ability created by imprinting the additives was lost when the CPM was heated at a high temperature, and was recovered by contacting it with the additive in a packed column. The structural change in 2a during these treatments was not clearly detected by spectroscopic methods.