190518-91-3Relevant academic research and scientific papers
Synthesis, structure and stability of E/Z-isomers of novel conjugated enamines prepared from 9-arylmethyl- or 9-arylpropenyl-9H-carbazole with arylmethyleneanilines
Paventi, Martino,Hay, Allan S.
, p. 1059 - 1068 (2007/10/03)
Active methylene groups, substituted by 9H-carbazol-9-yl (Carb) and aryl or 2-phenylethenyl groups, condense with arylmethyleneanilines in DMF at 75°C in the presence of Bu'OK to form the corresponding enamines [(Carb)(Ar1)C=C(Ar2)H] and dienamines [(Ar3)HC=C(Carb)CH=CHPh] in almost quantitative yield. The 1H and 13C NMR spectra for the enamine 1′Z-isomers [16 (Ar1 = Ar2 = 4-fluorophenyl), 17 (Ar1 = 4-fluorophenyl, Ar2 = 4-tert-butoxyphenyl), 19 (Ar1 = Ar2 = 4-tert-butoxyphenyl)], dienamine 1′Z-isomers [14a (Ar3 = 1-naphthyl), 14b (Ar3 = 4-methoxyphenyl), 14c (Ar3 = Ph)] and 1′E-isomers [15a (Ar3 = 1-naphthyl), 15c (Ar3 = Ph)] and precursors are assigned with the aid of COSY, HMBC, and HMQC techniques. The geometrical isomerism of the different dienamines 14-15 is established by 3JC-H NMR couplings and that of enamine 12 by a difference NOE experiment. X-Ray crystal structures for 16, 14a and 15c corroborate the isomerism results deduced by NMR studies. Dienamines 14a and 15a hydrolyse to the ketone under relatively strong acid conditions [AcOH-HCl-H2O (18:1:1 v/v)] under reflux over 7 h. There is an equilibrium between 14c and 15c in 1,2,4-trichlorobenzene at 180 ± 1°C with K = 15c/14c = 0.77 as estimated from the kinetic rate profiles from HPLC data acquired over 4 days. However, under the same conditions, 14a and 15a undergo an equilibration concurrent with a reaction (monitored over 9 days) giving apparently a carbazolyl-substituted phenylphenanthrene. In contrast, enamine 16 is thermally stable with no detectable change after boiling for 4 days in 1,2,4-trichlorobenzene.
