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.