4:7,10:13-Diepoxy-1-aza[16]annulene and 3:6,9:12,15:18-triepoxy-2-chloro-1-aza-[18]annulene as the first examples of oxygen-bridged aza-[4n]- and -[4n+ 2]annulenes

Abstract

The title compounds were prepared by the Beckmann rearrangement of diepoxy[15]- and triepoxy[17]-annulenone oximes (2) and (11), respectively; 4:7,10:13-diepoxy-1-aza[16]annulene (5) exists as two tautomers, the keto form (5a) and the dipolar form (5b), forming a paratropic 16π system; 3:6,9:12,15:18-triepoxy-2-chloro-1-aza-[18]annulene (12) proved to be strongly diatropic (18π).