Surprising reactions or special azoolefins - self-arylation, indole ring closure, mild chlorine substitution, and “tert. amino effect”

Ring Closure of Azo Compounds to 1,2-Annulated Benzimidazole Derivatives and Further Evidence of Reversibility of the Azo-Coupling Reaction

“…The first instance of such cyclization was originally reported in 1895 30 when 1,2-dimethylbenzimidazole was unexpectedly obtained by prolonged reflux of o-aminodimethylaniline in acetic anhydride. The formation of benzimidazole derivatives from azo compounds has been reported in a few cases 25,26,31 beginning with N,N-dialkylamino ortho-substituted azobenzenes: also in these cases the tert-amino effect is operative. In this context, formation of benzimidazoles from azoderivatives 7 and 8 represents a further extension of this cyclization, and a possible reaction pathway involving a proton transfer or internal (intramolecular) salification (Scheme 4), in which both ammonium ions are proximal to the diazo group that is being cleaved, thus favoring the cleavage.…”

“…The first instance of such cyclization was originally reported in 1895 when 1,2-dimethylbenzimidazole was unexpectedly obtained by prolonged reflux of o -aminodimethylaniline in acetic anhydride. The formation of benzimidazole derivatives from azo compounds has been reported in a few cases ,, beginning with N , N -dialkylamino ortho-substituted azobenzenes: also in these cases the tert-amino effect is operative.…”

The tert-amino effect in heterocyclic chemistry: Synthesis of new fused pyrazolinoquinolizine and 1,4-oxazinopyrazoline derivatives

“…The first reaction of this type was reported in 1895 by Pinnow. [ 12 ] Most of the early examples of the reaction of compounds with an unsaturated ortho -substituent involve groups with at least one heteroatom, such as nitroso,[ 13 ] nitro,[ 14 , 15 ] azo,[ 16 ] amine,[ 17 ] azomethine, [ 18 - 20 ] carbonyl, [ 20 - 23 ] or thiocarbonyl moieties as the ortho substituents. [ 24 ] The application of the tert -amino effect to the synthesis of pyrido-fused benzenes, pyridazines and uracils has also been reported.…”

The tert‐Amino Effect in Heterocyclic Chemistry: Synthesis of Spiroheterocycles

“…The first reaction of this type was reported in 1895 by Pinnow [2]. Most of the early examples of the reaction of compounds with an unsaturated ortho substituted involve groups with at least one heteroatom, such as nitroso [3], nitro [4][5], azo [6], amine [7], azomethine [8][9][10], carbonyl [11][12][13] or thiocarbonyl moieties as the ortho substituents [14]. derivatives.…”