A Novel Synthesis of Indole and Quinoline Derivatives from Aniline and 1, 2- or 1, 3-Diols

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1. (1) Syntheses of Indole Derivatives from 2- (2-Aminophenyl) ethanol and 2- (2-Nitrophenyl) ethanol : When 2- (2-aminophenyl) ethanols (3), which were easily prepared by condensation between the corresponding 2-nitrotoluene (1) and aldehydes followed by reduction, were treated with a catalytic amount of RuCl_2(PPh_3)_3 (2 mol%) under reflux in toluene for 6 h, the corresponding indoles (4) were readily obtained in high to excellent yields (73-100 %).1. (2) Plots of -ln vs time were linear over 70 % conversions of (3), where x is the amount of indoles (4) formed and a_0 is the amount of (3) charged. Furthermore, a straight line with a zero intercept was obtained on plotting the observed rate constants against the different initial catalyst concentrations ([RuCl6.10 x 10-2.44 x 10 mol dm^<-3>). Thus the rate law for the present indole synthesis is expressed by the following equation.d[(4)]/dt=kappa_<obs>[RuCl_2(PPh_3)_3]_0[(3)]1. (3) With a heterogeneous (Pd/C or Rh/C) and homogeneous (RuCl_2(PPh_3)_3 binary catalyst system, indoles were afforded in one pot from 2- (2-nitrophenyl) ethanols (2) under a hydrogen atmosphere.2. (1) Synthesis of Indole from Aniline and Ethylene Glycol : When the reaction of aniline with ethylene glyol was performed (aniline/ethylene glycol=1.0/1.5) in the presence of a catalytic amount of RuCl, 1.4-diphenylpiperazine was mainly obtained. However, when the molar ration of aniline/ethylene glycol was increased from 1.0/1.5 to 10/1.0, indole was obtained in 8 % yield together with a considerable amount of N, N'-diphenylethylenediamine. At this stage, RuClO - dppe is the most suitable catalyst system for the synthesis of indole from aniline and ethylene glycol (18 % yield).2. (2) N- (Trimethylsilyl) aniline and acetanilide, which were protected compounds of aniline, did not react with ethylene glycol and the corresponding indoles were not obtained at all.