2,3-Dihydro-I H-I ,4-diazepines are normally brominated at the 6-position. Phenyl substituents are usually unaffected, although with 2.3-dihydro-I .4-diphenyl-5,7-dimethyl-1H-l,4-diazepinium salts, the benzene rings are also brominated. 2.3-Dihydro-I ,7-dimethyl-5-phenyl-1 H -I ,4-diazepine is brominated at the 7-methyl group. N-Chlorosuccinimide and N-iodosuccinimide also substitute dihydrodiazepines at the 6-position. Under appropriate conditions 6.6-dihalogenodihydro-6H-diazepines have been isolated, but they revert to monohalogenocompounds in dilute hydrobromic acid. 6-Bromodihydro-I H-diazepinium salts are debrominated by strong acid in the presence of bromide ion.With nucleophiles, 6-bromodihydro-I H-diazepines either undergo normal nucleophilic substitution or suffer replacement of the bromine by hydrogen.THE most characteristic feature of the chemistry of the 2,3-dihydro-lH-1,4-diazepinium cations is the readiness with which they undergo electrophilic substitution at the fi-position, with retention of the initial mesomeric ~y s t e m . ~, ~ Because of this behaviour they have been described as quasi-aromatic corn pound^.^*^ A study
Triphenyland Tetraphenyl-diazocyclopentadienesBy Douglas Lloyd and F. I. Wasson New methods for the preparation of 2,3,4-triphenyl-and 2,3,4,5-tetraphenyl-diazocyclopentadiene are described.The former undergoes electrophilic substitution a t the 5-position. Other reactions of these compounds are mentioned.THE first diazocyclopentadiene to be prepared was diazofluorene, in 1921, by oxidation of fluorenone hydrazone.2 In 1953 diazocyclopentadiene itself (I) was prepared by the reaction between lithium cyclopentadienide and toluene-p-sulphonyl azide.3 The same method has since been used to prepare 2,3,4-triphen~l-,~ 2,3,5-triphenyl-,5*6 and 2,3,4,5-tetraphenyl-diazocyclo-2 pentadienes.6 A variant on this method, using cyclopentadiene in the presence of an amine instead of a cyclopentadienide salt was recently utilised to prepare compound (I) .7 2,3,4-Triphenyl-and 2,3,4,5-tetraphenyl-diazocyclopentadienes have now been prepared in greater yield by treating the corresponding dienes with toluene-$-sulphonyl azide in diethylamine at 0" for several days.
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