Indolizines: with special reference to the action of electrophilic reagents

Abstract

Indolizine was first synthesised by Scholts¹ in 1912 who proposed at that time the presently accepted ring structure (1). A number of alternative names and systems of numbering have been suggested for the heterocycle. These include pyrindole, pyrroline, pyrrosoline, 9 pyrrolopyridine and pyrrolo [1,2-a] pyridine. It is proposed to use the name indolozine and the numbering as shown in (1), in accordance with the recommendations of the I.U.P.A.C. Direct support for Scholts’ formulation of the structure of indolizine followed from its catalytic reduction² showing the presence of four double bonds, to a derivative identical with d-coniceine (a) (ostahydtoindolizine) which on degradation with ayanogen bromide yielded a1 condine (9-n-gropylpieridine). Further evidence substantiating this formulation of indolizine arises from consideration of numerous syntheses described below.