Characteristic Tautomerism and Isomerization in the Quinoxaline Chemistry

Abstract

Various side-chained quinoxalines have been found to exhibit the interesting tautomeric equilibria between the enamine and methylene imine forms and between the hydrazone imine and diazenyl enamine forms by means of the various spectroscopies.Moreover, some of the quinoxaline derivatives have also been known to isomerire from one tautorner into the other stable tautomer without the tautomeric equilibria in the media.This review describes the above quinoxalines exhibiting the above tautomeric eauilibria and isomerizations.This review includes the fallowing contents.I. Introduction 11.Tautomeric Equilibria between Enamine and Methylene Imine Forms 1. 3 -A l k o x y c a r b o n y l m e t h y l e n e -2 -o x a l , l , 2 , 3 , 4 -t e t h y d q u i n x a l i n e s and Related Compounds 2. 3-Heteroarylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxalines a. 3-Oxadiazolylmethylene-and 3 -T r i a z o l y l m e t h y l e n e -2 -0 x o -1 ~2 ~3 ~4 -t e t r ahydroquinoxalines b. 3 -B e n z i m i d a z o l y l m e t h y l e n e -2 -0 ~o -1 , 2 , 3 , 4 -t e t r h y d r o q u i n o x a l i n e and Its Hydrochloride 3 .3-(a-ilydroxy)heteroarylmethylene-2oxo-1,2,3,4-tetrahydroquinoxalines and Related Compounds 4 .3-(a-Hydroxyimina)triazolylmethyl-2-0~0-1,2-dihydroquinoxalines 111.Tautomeric Equilibria between Hydrazone Imine and Diazenyl Enamine Forms