Abstract
The [π4s+π2s] cycloaddition between cyclobutene derivatives and s- tetrazines formed unstable adducts which readily lost nitrogen to yield the complex dihydro-pyridazines (17). The structure of these products was assigned on the basis of spectral data. In addition, the thermolysis of these compounds has been investigated as a potential route to 1,2-diazocines (or valence isomers thereof). These results have been discussed and compared with the related mass spectral fragmentations. While the free 1,2-diazocines could not be isolated by this scheme it did afford a versatile route to the [π4s + π2s] cycloadducts of the valence isomeric 3,4-diazabicyclo[4,2,0]octa-2,4,7- triene system. In particular 1,8-di(2?-pyridyl) and 1,8-diphenyl-13,14- diazapentacyclo-[6,4,2,13,6,02,7,09,12]pentadeca-4,10,13-triene (24a,b) were prepared, the exact stereochemistry being confirmed by studies of the lanthanide-induced chemical shift. ��� The reaction of cis-3,4-dichlorocyclobutene and 3,6-di(2?-pyridyl)- s-tetrazine formed an ionic compound, 8a-amnia-3,4-diazaphenanthrene chloride (13), which contains a new heterocyclic ring system. This structure has been confirmed by a single-crystal X-ray analysis.
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