Synthesis of derivatives of aza[14]annulene, aza[16]annulene, aza[18]annulene, aza[20]annulene, and aza[22]annulene, diatropic and paratropic vinylogues of pyridine

Abstract

Syntheses of the tetradehydroaza[14]annulene (5), the tetradehydroazabenz[14]annulene (6), the tetra-dehydroazadibenz[14]annulene (7), the tetradehydroaza[16]annulene (8), the tetradehydroaza[18]-annulene (9), the tetradehydroaza[20]annulene (10), and the tetradehydroaza[22]annulene (11) are described. The aza[16]annulene (8) and the aza[20]annulene (10) are the first examples of monocyclic aza-annulenes to show a paramagnetic ring current. The lactams, the precursors of these aza-annulenes, proved to exist in zwitterionic forms and to exhibit tropic behaviour. Comparison with the carbocyclic annulene series is made on the basis of ¹H n.m.r. and electronic spectra of these compounds.