Chin. J. Org. Chem. ›› 2001, Vol. 21 ›› Issue (11): 898-903.

1. 中国科学技术大学化学系.合肥(230026);兰州大学应用有机化学国家重点实验 室.兰州(730000)
• 发布日期:2001-11-25

### Study on the mechanism of reduction of activated ethylenes with coenzyme NADH models

Liu Youcheng;Li Jin

1. Univ Sci & Technol China, Dept Chem.Hefei(230026);Lanzhou Univ, State Key Lab Appl Organ Chem.Lanzhou(730000)
• Published:2001-11-25

The reduction of a series of 2-bromo-1-(X-phenyl)ethylidene malonic derivatives with Coenzyme NADH models has been investigated. Depending on the structrue of substrates and that of the model, hydride transfer mechanism and electron transfer mechanism could be differentiated. Thus, the reaction of 4-benzyl-1, 4- dihydronicotinamide (BNAH) with 2-bromo-1- phenylethylidenemalononitrile produced 2-phenylcyclopropane-1, 1- dinitrile through hydride transfer mechanism, while the reaction of 10- methyl-9, 10- dihydroacridine with 2-bromo-1- phenylethylidenemalononitrile gave 1-phenylethylidenemalononitrile through electron transfer, debromination and hydrogen abstraction mechanism. Studies on substituent effect and kinetic isotope effect support the conclusion. Using (Ss)-1-benzyl-3-(p-tolylsulfinyl)-1, 4- dihydropyridine as a chiral NADH model, the synthesis of phenylcyclopropane derivatives with moderate optical activity has been achieved. Based on the evidence of kinetic isotope effect and trapping with oxygen, the reduction of 1, 1-diphenyl-2, 2- dinitroethylene with BNAH has been shown to proceed through a transition state of partial diradical and partial covalent bonding character. This was caused by steric hindrance of the substituent phenyl and nitro groups as demonstrated by X-ray crystallographic analysis of the substrate molecule. This provides evidence for the existence of an "intermediate mechanism" between polar mechanism and electron transfer mechanism according to Pross-Shaik "Curve Crossing Model". The reduction of 9-fluorenylidenemalononitrile with BNAH proceeded through electron transfer and the intermediacy of a carbanion with negative charge on C-9 of fluorenyl nucleus and showed a kinetic H/D isotope effect of 2.6. Further research work is in progress.

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