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Enantiotopic-Group Differentiation. Asymmetric Monoesterification of Malonic Acids Using Cinchona Alkaloid Derivatives
20 August 2002 (online)
2,2-Dimethyl-5-methyl-5-phenyl-4,6-dioxo-1,3-dioxane (1) was cleaved asymmetrically, by nucleophilic attack of primary alkoxide ions, paired with N-benzylquaternary ammonium cations, derived from cinchona alkaloids, to give optically active monoalkyl malonates 3 with moderate setereoselectivity. The ester group of 3 was selectively reduced to afford optically active α-methyltropic acid (5) in good yield. The relationship between the structure of ammonium cations and the direction of stereoselectivity is described.