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题名: Rapid Access to Substituted Piperazines via Ti(NMe2)(4)-Mediated C-CBond-Making Reactions
作者: Chen, Zhou ;  Wu, Jian ;  Chen, Yanmei ;  Li, Lei ;  Xia, Yuanzhi ;  Li, Yahong ;  Liu, Wei ;  Lei, Tao ;  Yang, Lijuan ;  高丹丹 ;  李武
刊名: ORGANOMETALLICS
出版日期: 2012
卷号: 31, 期号:17, 页码:6005-6013
英文摘要: An efficient Ti(NMe2)(4)-mediated C-C bond-forming methodology toward substituted piperazines, the basic skeleton of several biologically active natural products, has been developed. In reactions of tridentate monoanionic ligands bearing a [-HCNCH2-] linkage with Ti(NMe2)(4), unusual [3 + 3] dimerized complexes through C-C coupling of the putative titanium aza-allyl complex intermediate could be obtained. These complexes contain substituted piperazine backbones and could give rise efficiently to substituted piperazine derivatives via hydrolysis. Treatment of Ti(NMe2)(4) with a series of tridentate dianionic and bidentate monoanionic ligands bearing the [-HCNCH2-] moiety only generated chelated titanium complexes from ligand exchange reactions. Mechanistic studies using DFT/M06 calculations revealed that the methylene in the [-HCNCH2-] moiety of titanium complexes bearing tridentate monoanionic ligands could be deprotonated intramolecularly by dimethylamide anion with an activation energy of about 22 kcal/mol. The resulting titanium aza-allyl complexes from this beta-H abstraction step then undergo a consecutive stepwise [3 + 2] cycloaddition/ring expansion reaction facilely to form the dimerized complex. However, beta-H abstractions for Ti complexes bearing tridentate dianionic and bidentate monoanionic ligands were energetically demanding, as the negative charges could not be stabilized by the adjacent groups in the possible intermediates, explaining the experimental outcomes that no C-C coupled products were formed. An efficient Ti(NMe2)(4)-mediated C-C bond-forming methodology toward substituted piperazines, the basic skeleton of several biologically active natural products, has been developed. In reactions of tridentate monoanionic ligands bearing a [-HCNCH2-] linkage with Ti(NMe2)(4), unusual [3 + 3] dimerized complexes through C-C coupling of the putative titanium aza-allyl complex intermediate could be obtained. These complexes contain substituted piperazine backbones and could give rise efficiently to substituted piperazine derivatives via hydrolysis. Treatment of Ti(NMe2)(4) with a series of tridentate dianionic and bidentate monoanionic ligands bearing the [-HCNCH2-] moiety only generated chelated titanium complexes from ligand exchange reactions. Mechanistic studies using DFT/M06 calculations revealed that the methylene in the [-HCNCH2-] moiety of titanium complexes bearing tridentate monoanionic ligands could be deprotonated intramolecularly by dimethylamide anion with an activation energy of about 22 kcal/mol. The resulting titanium aza-allyl complexes from this beta-H abstraction step then undergo a consecutive stepwise [3 + 2] cycloaddition/ring expansion reaction facilely to form the dimerized complex. However, beta-H abstractions for Ti complexes bearing tridentate dianionic and bidentate monoanionic ligands were energetically demanding, as the negative charges could not be stabilized by the adjacent groups in the possible intermediates, explaining the experimental outcomes that no C-C coupled products were formed.
收录类别: SCI
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内容类型: 期刊论文
URI标识: http://ir.isl.ac.cn/handle/363002/2025
Appears in Collections:青海盐湖研究所知识仓储(2014年之前)_期刊论文

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Recommended Citation:
Chen, Zhou,Wu, Jian,Chen, Yanmei,et al. Rapid Access to Substituted Piperazines via Ti(NMe2)(4)-Mediated C-CBond-Making Reactions[J]. ORGANOMETALLICS,2012,31(17):6005-6013.
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