Heterocyclische Verbindungen aus Zuckern, XV: Zur Konfiguration chiraler C-2-substituierter 4-Thiazolidincarbons�uren. Chiralit�tstransfer auf C-3 in 3,4-Dihydro-1H-pyrrolo[1,2-c]thiazolen
摘要:
5-Substituted 3,4-dihydro-pyrrolo[1,2-c]thiazole-6,7-dicarboxylic acid esters 3 are obtained from 2-substituted-3-acyl-1,3-thiazolidine-4-carboxylic acids, 1 in [3 + 2]-cycloaddition reactions via mesoionic oxazolone (''munchnone'') intermediates. The chirality at C-4 of the starting carboxylic acids 1 is eliminated in the products 3, and the chirality at C-3 (C-2 in the starting carboxylic acids 1) can thus be determined through chiroptical measurements. Several representatives of the ring system 3 have been characterised through H-1- and CD-spectra and the molecular structure of (3S)-3da has been determined by X-ray crystallography.
Epimerization at C-2 of 2-substituted thiazolidine-4-carboxylic acids
作者:H. T. Nagasawa、D. J. W. Goon、F. N. Shirota
DOI:10.1002/jhet.5570180538
日期:1981.8
boxylic acid (1a), with a 3.3 to 1 predominance of the 2S (cis) isomer, was shown to epimerize at the C-2 position in neutral, protic solvents. This was manifested by mutarotation concomitant to changes in the ratios of the C-4 methine proton resonances in the nmr spectrum. Compound 1a was stable in dilute sodium carbonate solution, but underwent rapid equilibration in 1N hydrochloric acid.