2-Amino-5-thiazolo quinoline

The first thiazoloquinolines, namely angularly annelated 2-methyl-thiazolo [4,5-/]quinoline 19 and linearly annelated 2-methyl-thiazolo[4,5-g]quinoline 20, were prepared in 1937 in poor yield using the Skraup reaction and exploiting the blockage of position 4 in 5-amino-2-methylbenzothiazole with a chlorine atom, as shown in Scheme 10 (37LA60). 

The isomeric thiazolo[5,4-g]quinoline skeleton was prepared from 6-chloro-quinoline-5,8-dione hydrochloride by reaction with thiourea, resulting in the 2-amino-4,9-dioxo-4,9-dihydroderivative 42 (91CCC1919). 

The Wittig-type reactions of iminophosphoranes with isocyanates and related compounds have also been extensively used in heterocyclic synthesis. Examples include the preparations of the mesoionic [l,3,4]thiadiazolo[2,3-c][l,2,4]triazines (210) from (209), 0 bicyclic guanidines, e.g. (212), from (211), naphthypyridines (215), (216), and (217) from (213) and (214), 2 pyrido[l,2-f]pyrimido-[4,5-d)pyrimidines (218), 7H-pyrido-[4,3-c]- (219) and 10H-pyrido[3,4-b]- (220) carbazoles, tricyclic fused 2,4-diimino-l,3-diazetidines (222) from the bisiminophosphorane (221), benzotriazepines (225) from (223) and (224), 6 and mesoionic thiazolo-[2,3-b]-1,3,4-thiadiazoles (227) and N,N-bisheteroarylamines from the iminophosphorane (226), derived from 3-amino-4-phenylthiazole-2(3H)-thione. The carbodiimides (229), prepared from the iminophosphorane (228), can be converted into quinolines or a-carboline derivatives depending on the nature of the isocyanate used in the reaction with (228) and the reactions of iminophosphoranes (230) and (231) with aryl and styryl isocyanates provide one-pot syntheses of quinoline, a-carboline, and quinindoline derivatives. 9... 

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