Chapter 37 - Fused heterocyclic systems having a nitrogen atom common to two or more rings

Abstract

This chapter reviews the chemistry of indolizines, and their hydrogenated derivatives. Indolizines are prepared from quaternary pyridium salts by carbonyl condensation reactions, Tschitschibabin reaction, or pericyclic reactions via the pyridinium ylides. Indolizine and alkali derivatives are easily oxidized even by exposure to air. Indolizine derivatives hydrogenated only in the pyridine ring are accessible by cyclization of N -substituted pyrroles. 1,3-cycloaddition reactions of pyridinium ylides can be carried out with olefinic dipolarophiles, a notable example of which is phenyl vinyl sulfoxide. The most important reactions of quinolizinium salts are nucleophilic addition and substitution. Among the more novel routes to indolizidines is the transannular cyclization of azonines. The indolizidine ring system may be constructed in one step from an acyclic precursor by making use of an intramolecular Diels–Alder reaction. A new and very simple route to the iminium salts is provided by heating N -(carboxyalkyl) lactams with soda-lime and treatment of the resulting enamines with perchloric acid. [2.2.3] cyclazines are prepared from 3 H -pyrrolizine and its derivatives by heating with the vinamidinium salt and sodium hydride in N , N -dimethylformamide.