Catalytic Asymmetric Mannich-Type Reaction Enabled by Efficient Dienolization of α,β-Unsaturated Pyrazoleamides

• 作者: Hai-Jun Zhang Feng Zhong Yan-Cheng Xie Liang Yin
• 来源期刊: 中国化学（英文版）
• 年，卷（期）: 2021,（1）
• 所属期刊栏目: Concise Reports
• 页码范围: 55-61
• 页数: 7页
• 语种: 英文
• DOI: 10.1002/cjoc.202000432

摘要

(E)-α,β-Unsaturated pyrazoleamides undergo facile dienolization to furnish copper(Ⅰ)-(1Z,3Z)-dienolates as the major in the presence of a copper(Ⅰ)-(R)-DTBM-SEGPHOS catalyst and Et3N,which react with aldimines to afford syn-vinylogous products as the major dia-stereoisomers in high regio-and enantioselectivities.In some cases,the diastereoselectivity is low,possibly due to the low ratio of copper(Ⅰ)-(1Z,3Z)-dienolates to copper(Ⅰ)-(1Z,3E)-dienolates.(Z)-Allylcopper(Ⅰ)species is proposed as effective intermediates,which may form an equilibrium with copper(Ⅰ)-(1Z,3Z)-dienolates.Interestingly,the present methodology is a nice complement to our pre-vious report,in which(E)-β,γ-unsaturated pyrazoleamides were employed as the prenucleophiles in the copper(l)-catalyzed asym-metric vinylogous Mannich-Type reaction and anti-vinylogous products were obtained.In the previous reaction,copper(Ⅰ)-(1Z,3E)-dienolates were generated through α-deprotonation,which might form an equilibrium with(E)-allylcopper(Ⅰ)species.There-fore,it is realized in the presence of a copper(Ⅰ)catalyst that(E)-α,β-unsaturated pyrazoleamides lead to syn-products and(E)-β,γ-unsaturated pyrazoleamides lead to anti-products.Finally,by use of(E)-β,γ-unsaturated pyrazoleamide,(E)-α,β-unsaturated pyrazoleamide,(R)-DTBM-SEGPHOS,and(S)-DTBM-SEGPHOS,the stereodivergent synthesis of all four stereoisomers is successfully carried out.Then by following a three-step reaction sequence,all four stereoisomers of N-Boc-2-Ph-3-Me-piperidine are synthesized in good yields,which potentially serve as common structure units in pharmaceutically active compounds.