Thioenols and thioamides substituted by twoβ-EWGs. Comparison with analogous amides and enols

Autor:	Zvi Rappoport, Ahmad Basheer
Rok vydání:	2008
Předmět:	Sh groups Hydrogen bond Stereochemistry Organic Chemistry Crystallographic data Keto–enol tautomerism Enol Medicinal chemistry chemistry.chemical_compound chemistry Intramolecular force Physical and Theoretical Chemistry Methylene Thioenol
Zdroj:	Journal of Physical Organic Chemistry. 21:483-491
ISSN:	1099-1395 0894-3230
Popis:	Condensation of organic isothiocyanates with active methylene compounds gave nine thioamides RNHCSCHYY′ or their isomeric thioenols RNHC(SH) = CYY′ for substrates in which Y and Y′ are electron-withdrawing groups (EWG). These included derivatives of Meldrum's acid (MA) which showed 100% thioenol in all solvents. For other compounds the percentages of thioenol in CDCl3 when R = Ph are 100% when Y = CN and Y′ = CO2Me or Y′ = CO2CH2CCl3, 6% when Y = Y′ = CO2CH2CF3, and 0% when Y = Y′ = CO2Me. The chemical shift of SH (highest values 12.0–16.0 ppm) served as a probe for the thioenol structures and also for the extent of hydrogen bonding to the SH group. In contrast to simple ketones and thioketones in which thioenolization is favored over enolization by factors as large as 106, for intramolecular competition KThioenol/KEnol ratios are much lower than for systems not substituted by β-EWGs. X-ray crystallography of the 5-anilido-MA derivative shows a hydrogen-bonded thioenol structure. δ(OH), δ(NH), KEnol, and crystallographic data for analogous thioenol and enol systems are compared. Copyright © 2008 John Wiley & Sons, Ltd.
Databáze:	OpenAIRE
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