Ring-position isomer analogs

The 2,1-benzisoxazolium salts unsubstituted in the 3-position behave in an analogous manner to their 1,2-isomers above. Particularly interesting is the reaction of the salt (134) with EtaN. Abstraction of the C(3)-proton is followed by ring opening to the iminoketene (135) which undergoes electrocyclization to its stable valence tautomer (136) in 84% yield (71JA1543). 

The relation of activation by para vs. ortho ring-nitrogen in bicy-clics is altered by these special cases. For example, 4-chloroquinazoline (4-Cl-l,3-diaza) is much more reactive than the 2-chloro isomer (2-Cl-l,3-diaza) for two reasons, one being the poor activation in 2-Le-3-aza compounds. 4-Chloro-l,8-naphthyridine will be decreased in reactivity relative to its 2-chloro isomer due to the very poor activation in 4-Le-8-aza compounds and it may be only slightly more reactive than the mono-aza analog 4-chloroquinoline. The greater reactivity at the 2-position of 2,4-dichloro-l,8-naphthyri-dine 3 can be ascribed to this 4-Le-8-aza effect. ... 

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