Dipyrroloquinoxalines. 1. Synthesis of a new bisspiropyran system derived from benzo[e]pyrrolo[3,2-g]indole

Abstract

In previous work [1], we reported the synthesis of spirocyclic dihydroindolizine systems derived from 2,3,3,8,9,9-hexamethyl-3,8-dihydrobenzo[e]pyrrolo[3,2-g]indole (1). In a continuation of work on the synthesis of bisspiro compounds, we report the synthesis of a new bisspiro system, namely, 1',1',8',8'-tetramethyl1',4',5',8'-tetrahydrospiro[chromene-2,2'-dipyrrolo[1,2,3-d,e:3,2,1-i,j]benzo[g]quinoxaline-7',2"-chromene]. The alkylation of hexamethyldihydrobenzo[e]pyrrolo[3,2-g]indole 1 by dibromoethane gives a biquaternary salt, which was converted by treatment with 5% aqueous KOH into the bisanalog of 2-methyleneindoline bases known as Fischer bases, namely, 1,1,8,8-tetramethyl-2,7-dimethylidene-1,2,4,5,7,8-hexahydrodipyrrolo[1,2,3-d,e:3,2,1-i,j]benzo[g]quinoxaline (2). 2-Methylideneindoline bases are important intermediates in the synthesis of a variety of organic compounds [2].