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Thioenols and thioamides substituted by two β ‐EWGs. Comparison with analogous amides and enols
Author(s) -
Basheer Ahmad,
Rappoport Zvi
Publication year - 2008
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1359
Subject(s) - chemistry , enol , intramolecular force , keto–enol tautomerism , hydrogen bond , methylene , medicinal chemistry , stereochemistry , tautomer , organic chemistry , molecule , catalysis
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 CDCl 3 when R = Ph are 100% when Y = CN and Y′ = CO 2 Me or Y′ = CO 2 CH 2 CCl 3 , 6% when Y = Y′ = CO 2 CH 2 CF 3 , and 0% when Y = Y′ = CO 2 Me. 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 10 6 , for intramolecular competition K Thioenol / K Enol 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), K Enol , and crystallographic data for analogous thioenol and enol systems are compared. Copyright © 2008 John Wiley & Sons, Ltd.