Tropylidene-norcaradiene

It has been known for many years that substituents can change the position of the tropylidene-norcaradiene (4 5) equilibrium (equation 4). While the parent compound... 

Another example of bromotropone contraction is derived from Nozoe s benzotropazine chemistry [Scheme 146 89H(29)1459]. Condensation of tropone 552 with further o-aminothiophenol (117b) gave benzenoid compound 554 instead of the expected tris(benzazino)tropylidene. Presumably, this condensation takes place via initial cyclization (to benzothiazine), then cyclocondensation (to spirobenzothiazoline), followed by tautomerization (to norcaradiene 553), ring contraction, and dehydrogenation. 

The presence of the methoxycarbonyl substituent at C-7 affects the reaction course of the cycloaddition of diethyl diazenedicarboxylate to the cycloheptatriene moiety, since the ene product is not produced. A mixture of tropylidene- and norcaradiene-type adducts 8 and 9 is obtained, whose ratio is dependent on the temperature13. 4-Phenyl-3//-l,2,4-triazole-3,5(4//)-dione, however, affords the norcaradiene-type adducts 10 exclusively with 7-substituted cyclo-heptatrienes14"19. 

The cycloaddition of 4-phenyl-3//-l,2,4-triazole-3,5(4//)-dione to a [2,6]spirocyclohepta-triene. which cannot equilibrate with the norcaradiene-type valence tautomer, affords two diastereomeric tropylidene-type adducts23. 

An examination has been made of substituent effects on the product distribution of tropylidene- and norcaradiene-derived endoperoxides arising on singlet oxygenation of 7-aryl- and 7-alkylcyclohepta-l,3,5-trienes. The ratio... 

---