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N ‐Isopropyl enols of carboxylic acid amides
Author(s) -
Lei Yi Xiong,
Casarini Daniele,
Cerioni Giovanni,
Rappoport Zvi
Publication year - 2003
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.629
Subject(s) - chemistry , enol , isopropyl , amide , stereochemistry , solvent , residue (chemistry) , medicinal chemistry , nuclear magnetic resonance spectroscopy , keto–enol tautomerism , tautomer , organic chemistry , catalysis
Abstract Eight N ‐isopropyl compounds of the formal structure YY′CHCONHPr‐ i ( 6 ), Y,Y′ = CO 2 Me, CO 2 CH 2 CF 3 , CN; YY′ = Meldrum′s acid residue; Y = CO 2 Me, Y′ = CO 2 CH 2 CF 3 , CN; Y = CO 2 CH 2 CF 3 , CO 2 CH(CF 3 ) 2 , Y′ = CN, and the N ‐ t ‐butyl derivative of Meldrum's acid were prepared and their structures were investigated in the solid state and in solution. The x‐ray diffraction data indicate that in the solid state the structure is that of the amide 6 , when Y = Y′ = CO 2 Me, whereas when Y = CO 2 Me, Y′ = CN or YY′ = Meldrum′s acid residue the structure is that of the enol ( 5 ) YY′C=C(OH)NHPr‐ i . The solid‐state 13 C spectra indicate structure 6 when Y = CO 2 Me, Y′ = CO 2 R, R = Me, CH 2 CF 3 and an enol structure for the other compounds studied. 1 H, 13 C and when available 19 F NMR spectra showed that the enol/amide composition in solution is structure and solvent dependent, in analogy with the previously investigated N ‐Ph analogs. The percentage of enol (and K Enol ) decrease in the order of solvents CCl 4 > CDCl 3 > THF‐ d 8 > CD 3 CN > DMSO‐ d 6 , DMF‐ d 7 . For Y,Y′ the percentage of enol increases when the number of fluorine atoms in R of the CO 2 R increases, when CN replaces a CO 2 R group or for the cyclic Meldrum's acid derivative. Both E ‐ and Z ‐enols were observed when Y ≠ Y′, mostly at low temperature. The δ(OH) values increase with increased polarity of the medium and with increased strength of the hydrogen bonds in which they are involved. In THF‐ d 8 and DMF‐ d 7 the Z ‐enol/ E ‐enol and the amide/enol ratios increase with increase in temperature. A main conclusion from the work is that the percentage of the enol increases, but not drastically, when the N ‐substituent is changed from Ph to i ‐Pr. Copyright © 2003 John Wiley & Sons, Ltd.