光学活性な菊酸の不斉合成用触媒の高効率化
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概要
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New practical catalysts have been developed for asymmetric cyclopropanation of 2, 5-dimethyl-2, 4-hexadiene with <I>tert</I>-butyl diazoacetate. First, the effects of the substituents on the salicylaldehyde moiety in the copper Schiff-base complex on the catalytic activity and the stereoselectivities were investigated. As a result, a substitution at the 5-position of hydrogen with the nitro-group on the salicylaldehyde moiety was found to enhance the catalytic efficiency. In addition, a combination catalyst of the copper Schiff-base complex with a Lewis acid was found to enhance the catalytic efficiency and achieved 90% chemical yield and 91% ee at 20°C with 0.1 mol% catalyst loading. Then, new cationic bisoxazoline-copper complex catalysts with PF<SUB>6</SUB><SUP>-</SUP>as the counter ion were demonstrated to achieve the highest stereoselectivities (<I>trans/cis</I> = 88/12, 96% ee at 0°C) with <I>tert</I>-butyl diazoacetate. Furthermore, the asymmetric induction mechanism of the cyclopropanation reaction catalyzed by each complex was studied with density functional calculations.
- 社団法人 有機合成化学協会の論文
- 2006-12-01