Aza-o-quinodimethane

Azabutadiene systems, as more or less formal carbonyl derivatives, have been used for [4 + 2] cycloaddition reactions. The fluoride-induced stereoselective transformation of (144) to the polycyclic steroid-like system (145), obviously proceeding via the corresponding reactive aza-o-quinodimethane (Scheme 67), shows the synthetic utility of such heterodienes. 

Benzoxathiazine derivatives 13 cannot show antiaromatic character. Hexahydro derivatives of 13 are known.35 The formation of systems of type 14 with aza-o-quinodimethane character is not favored. The constitution of the 3,2,l-benzoxathiazin-4(l//)-one 2-oxide 15 (R = H),36 which has only recently been reassigned37 to the originally postulated acyclic structure 16,38 is still under discussion. 

Phenanthrene o-quinodimethane, 55 Phenyl-2-aza-l,3-pentadiene, 258 6-Phenyl-5-azaazulene, 260... 

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