The Cycloheptatriene-Norcaradiene System. II.¹ Reactions of 7,7-Dicyanonorcaradienes

Cyclic and Acyclic N═N Bonds in Reactions with Some Alkenes and Dienes

“…The DA reaction rates of 1 with cycloheptatriene 5 and with cyclooctatetraene 7 are of particular interest. Hundreds of papers deal with the possible equilibrium and reactivity of the valence tautomers and . The very active singlet oxygen 1 О 2 demonstrates a low selectivity in the DA reaction with 5 , giving 95% of 1,4‐adduct with the structure similar to 18 , and about 5% with a structure similar to that of 15 , whereas the less active and more selective dienophile 1 gives only the adduct 15 (Schemes , ).…”

“…We suggest that these factors, taken together, are likely to be the underlying cause of the reduced activity of the 1,3‐ and 3,5‐diene systems of cycloheptatriene ( 5 ) and, especially, of cyclooctatetraene ( 7 ) with all dienophiles. For the seven‐disubstituted cycloheptatrienes, the position of equilibrium, similar to , changes from an overwhelming share of tautomer 5 (≥99.9%, both R are H atoms) to that of the tautomer, analogous to 17 , (≥99.9%, both R are CN groups) . There is an active discussion whether the DA reaction of dienophiles takes place with dienes 5 and 7 or with their minor tautomers, i.e., norcaradiene, 17 , and bicyclo[4,2,0]octa‐2,4,7‐triene, 20 , respectively (Fig.…”

Carbalkoxycarbenes

“…Whereas 9-bromofluorene reacted with ethyl diazoacetate in the presence of copper sulfate to afford only 9,9'-bifluorenylidene and ethyl bromoacetate,193 the corresponding reaction with 9-phenyl-9-bromofluorene (35a) afforded a condensation product in which a novel ring expansion had occurred to give ethyl 10-phenyl-9-phenanthrenecarboxylate (36a)206 (eq 40). With 36a, R = phenyl b, R = p-tolyl two condensation products were observed:206 the ringexpanded product (36b) and a second product, 37, analogous to the ethyl trlphenylacrylate (33) which had earlier been found in the corresponding copper catalyzed reaction of triphenylmethyl bromide with ethyl diazoace-tate205 (see eq 40 and eq 41).…”

Circumambulatory rearrangements of cyclopolyenes containing element-centred migrants

“…Migration of this type was directly observed at 77 8C in the study of the rearrangement of the corresponding dicyano derivative for which norcaradiene valence tautomer 67 is energetically more favourable than the 7,7-dicyanocycloheptatriene form. 185,186 Generally, such rearrangements are characterised by higher energy barriers compared to those corresponding to conditions of structural non-rigidity. 17,69,186 It was found that the migration of the methylene group around the aromatic ring is accompanied by the inversion of configuration of the migrating carbon atom 187 (contrary to the Woodward ± Hoffmann rules).…”