Preparation of chiral 1,2,4-triazolium salts as new NHC precatalysts
摘要:
The preparation of new chiral N,N'-disubstituted 1,2,4-triazolium based NHC salt precursors, Ia' and Ib, from phenylhydrazine and L-phenylalanine is reported. The 1,3,4-trisubstituted triazolium salt Ia' was obtained by a stepwise ring construction from L-phenylalanine via the corresponding imino ether and acetohydrazonamide, while a heterocyclic O-/N-heteroatom exchange strategy, based on a ring-opening/ring-closure of the oxadiazolium precursor, afforded the 1,4-disubstituted 1.2,4-triazolium salt Ib. The need for two different synthetic strategies is discussed. (c) 2012 Elsevier Ltd. All rights reserved.
Mesomeric betaine – N-heterocyclic carbene interconversions of 1,2,4-triazolium-phenolates. Sulfur, selenium, and borane adduct formation
作者:Ming Liu、Martin Nieger、Andreas Schmidt
DOI:10.1039/c4cc08032g
日期:——
The conjugated mesomeric betaines 2-(1-phenyl-4H-1,2,4-triazolium-4-yl)phenolates are masked N-heterocyclic carbenes of 1,2,4-triazole which can be trapped as thiones and selenones. Reaction with triethylborane and triphenylborane resulted in the formation of first representatives of a new zwitterionic heterocyclic ring system, benzo[e]1,2,4-triazolo[3,4-c][1,4,2]oxazaborinium-4-ide, as a formal trapping