Preparation of the elusive N-peri-annulated
planar
Blatter radicals was attempted using aza-Pschorr and photocyclization
methods. In both methods, substrates containing N–Me and N–Ac
groups yielded a zwitterionic heterocycle lacking the N-substituent
as the main product, while in one of them a carbazole derivative representing
a new heterocyclic system was also obtained. The formation of the
zwitterion and the carbazole suggests the formation of the desired
planar Blatter radical, which undergoes facile fragmentation through
homolysis of the N–R bond. This mechanism is supported by DFT
computational results, which also suggest that N-Ar
derivatives should be sufficiently stable for isolation. Electronic
structures of three planar Blatter radicals annulated with the O,
S, and N–Ph groups are compared