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[摘要]：Enantioselective deprotonative metalations of substituted ferrocenes using mixed lithium-metal bases are described. Using N,N-diisopropylferrocenecarboxamide as substrate, magnesium, iron, cobalt, zinc, and cadmium were tested as metals in bis[(S)-1-phenylethyl]amido-based combinations; after interception of the metalated species with iodine, very high enantiomeric excess (96?%) but low yield was obtained with cobalt, whereas zinc and cadmium only gave 27 and 30?%?ee, respectively, but in excellent yields. The small alkyl groups methyl and ethyl were identified as particularly suitable in the reaction using the putative dialkyl bis[(S)-1-phenylethyl]amido-based lithium and dilithium zincates. The dimethyl dilithium zincate was selected for a study of dependency on the temperature, reaction time, and amount of base. Increased enantioselectivities with temperature, reaction time, and amount of base were noted (ee = 86?% at 0 degrees C after 2 h, 2 equiv. of base). The best result using methyl ferrocenecarboxylate as substrate was observed without alkyl ligand. |
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