Formation of certain substituted 5H-pyrrolo[2,3-b]pyrazines by thermal cyclisation of pyrazinylhydrazones and a route to 5H-pyrazino[2,3-b]indole; a synthesis of 5H-pyrrolo[2,3-b] pyrazine and some of its properties

Abstract

Thermal (non-catalytic) cyclisation of the pyrazinylhydrazones (6a—i) caused ring closure on to the carbon atom of the pyrazine nucleus to give the 3-substituted and 2,3-disubstituted 5H-pyrrolo[2,3-b]pyrazines (7a—g), (8), and (9), respectively. 6,7,8,9-Tetrahydro-5H-pyrazino[2,3-b]indole (7g) was dehydrogenated to the parent pyrazino[2,3-b]indole (15). Pyrrolo[2,3-b]pyrazine (7h) has been obtained from 2-amino-3-methylpyrazine and some of its properties have been investigated.