Heteroaromalic compounds

Valence isomer formation is a feature also of the photochemistry of naphthalenes (3.33) and anthracenes for naphthalenes, as for benzenes, the extent ol steric crowding helps to determine which type of valence isomer predominates, since there is more severe interaction in the bicyclohexadiene products than in the benzvalene products. Amongst five-membered heteroaromalic compounds there are many known ring photoisomerizations that involve conversion of a 2-substituled to a 3-substituted system (e.g. 3.34). In some cases non-aromatic products can be isolated, such as bicyclo[2.1.0]pentene analogues from thiophenes 13.35). or acylcycfopropenes from furans (3.36) related species may be... 

Halogenation of heterocyclic compounds, 7, 1 Hammett equation, applications to heterocyclic compounds, 3, 209 20, 1 Hetarynes. 4, 121 Heleroadamanlane, 30, 80 Heleroannulenes, medium-large and large n-excessive 23, 55 Heteroaromalic compounds JV-aminoazonium salts, 29, 71 free-radical substitutions of, 2, 131... 

The displacement of bromine or chlorine atoms in heteroaromalic componnds is certainly one of the most effective synthetic methods leading to fluorinated heterocyclic compounds [13], For instance, heating 4,5,6-tribromo-l,2,3-triazine 1 with dry potassium fluoride at 550 C in vacuum results in the formation of a mixture of 4,5,6-trifluoro-l,2,3-triazine 2 and 5-bromo-4,6-difluoro-l,2,3-triazine 3 in the ratio 1 1 (Scheme 6) [14],... 

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