Direct Access to N-Unprotected α- and/or β-Tetrasubstituted Amino Acid Esters via Direct Catalytic Mannich-Type Reactions Using N-Unprotected Trifluoromethyl Ketimines

Masanao Sawa, Kazuhiro Morisaki, Yuta Kondo, Hiroyuki Morimoto, Takashi Ohshima

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Direct catalytic C−C bond-forming addition to N-unprotected ketimines is an efficient and straightforward method of synthesizing N-unprotected tetrasubstituted amines that eliminates prior protection/deprotection steps and allows facile transformation of the products. Despite its advantages, however, N-unprotected ketimines have difficulties in C−C bond-forming reactions, and only a limited number of reactions and substrates are reported compared with their N-protected counterparts. Herein we report that N-unprotected trifluoromethyl ketimines are effective for C−C bond-forming reactions using Mannich-type reactions as a model case. We demonstrate that Lewis acid catalysis was effective for promoting reactions with various N-unprotected trifluoromethyl ketimines, and thiourea organocatalysis was effective for promoting highly enantioselective reactions with various carbonyl nucleophiles, providing direct access to various N-unprotected α- and/or β-tetrasubstituted amino acid esters. Furthermore, direct construction of vicinal tetrasubstituted chiral carbon stereocenters was achieved for the first time in a highly enantio- and diastereoselective manner. These results demonstrate the potential of N-unprotected ketimines as substrates applicable to many other addition reactions.

Original languageEnglish
Pages (from-to)17022-17028
Number of pages7
JournalChemistry - A European Journal
Volume23
Issue number67
DOIs
Publication statusPublished - Dec 1 2017

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

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