Long-range substituent and temperature effect on prototropic tautomerism in 2-(acylmethyl)quinolines

Tautomeric equilibria between 2-(cinnamoylmethyl)quinoline. (Z)-1,2-dihydro -2-(cinnamoylmethylene)quinoline and (Z)-4-phenyl-1-(2-quinolyi)-1,3-butadi en-2-ol were studied by H-1, C-13 and N-15 NMR methods. The -CH=CH- fragmen t conjugated with phenyl and a strong electron donor p-(1-pyrrolidine) subs tituent were found to favour the enolimine tautomer. This undergoes fast ex change (on the NMR time-scale) with the enaminone form. The amount of the l atter tautomer was found to increase at low temperatures. Copyright (C) 200 1 John Wiley & Sons, Ltd.