2,3-Diazo-Dewar benzene

The formation of 1,3-dienes within a cyclic framework has been accomplished via extrusiem of molecular nitrogen. Cyclobutadiene has been obtained by nitrogen extrusion from 2,3-diazo-Dewar benzene, which is generated by mild oxidation of 2,3-dioxybicyclo[2.2.0]hex-S-ene. Other cyclic dienes that have been similarly obtained are cyclopentadiene and cyclohexa-1,3-diene from the corresponding diazo compounds. 

No general pattern can be recognized in the reaction of azides with cycloalkenes. Angle strain can greatly enhance the rate of azide addition to cycloalkenes, as shown by work on norbornene and its derivatives (Huisgen et al., 1965), on hexa-methylbicyclo[2.2.0]hexa-2,5-diene (Dewar benzene) (Paquette et al., 1972) and related compounds (review Lwowski, 1984, p. 579ff). Normally, dihydrotriazoles are primary products, followed by a dediazoniation to aziridines. Diazo compounds are formed only in rare cases, e.g., with trifluoromethylated Dewar thiophenes (Kobayashi et al., 1977, 1980). 

Cyclopropene diazo compound 327 treated with PTAD provides Dewar benzene analogue 330 in good yield (Scheme 56). Formation of this product is rationalized by way of intermediate dipolar urazole 328, which then undergoes a 1,2 shift to dipolar species 329, which collapses into the final product 330 (82CB3796). 

Trifluorodiazoethane has featured in investigations of perfluorobicyclo-[2,2,0]hexa-2,5-diene (perfluoro- Dewar -benzene) as a dipolarophile [- the 7If-tautomer (71) (75%) at 0— 20 C during 4 weeks]. Bis(trifluoromethyl)diazo-... 

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