Radical and Nitrenoid Reactivity of 3‑Halo-3-phenyldiazirines

3-Halo-3-phenyl-3<i>H</i>-diazirines (halogen = Br or Cl) undergo a dissociative single-electron transfer from alkyllithiums (RLi) in THF-based solvent mixtures. The resulting 3-phenyldiazirinyl radical, observed by EPR spectroscopy, is eventually transformed to benzonitrile. In Et₂O, 2 equiv of RLi add to both nitrogens of halodiazirine NN bond, affording <i>N,N</i>′-dialkylbenzamidines. The nitrenoid reactivity of some <i>N</i>-alkyl-1<i>H</i>-diazirine intermediates is manifested by their insertion into the α-C–H bond of THF or Et₂O

Evidence for the Cyclic CN₂ Carbene in Solution

Diazirinylidene (<i>c</i>-CN₂) is formally the simplest of the N-heterocyclic carbenes. The intermediacy of this elusive species in the fragmentation of butyl 3-bromodiazirine-3-car­box­ylate (<b>1a</b>) with pent-4-en-1-ols and their sodium alkoxides in DMF is supported by the formation of 2-oxa­bicyclo­[4.1.0]­heptanes and di­pen­tenoxy­methanes. These products result from an intramolecular [2 + 1] cycloaddition and O–H insertion, respectively, of penten­oxy­methyl­enes suggested to originate from the reaction of the electrophilic <i>c</i>-CN₂ with an alkoxide ion. The reaction of <b>1a</b> with primary or secondary amines in methanol affords the corresponding 3-bromo­diazirine-3-carbox­amides

Evidence for the Cyclic CN₂ Carbene in the Gas Phase

3-Halodiazirine-3-carboxylic acids (<i>c</i>-CN₂XCOOH, X = Cl or Br) were prepared from their esters and converted to the corresponding sodium salts. Collision-induced dissociation (CID) of the carboxylate ions led exclusively to the loss of CO₂ and the resulting <i>c</i>-CN₂X^– ions dissociated to <i>c</i>-CN₂ carbene at low energies. The bond dissociation energy (BDE) for <i>c</i>-CN₂Br^– was found to be less than 8 kcal/mol using CID of the anion generated by electrospray ionization of the carboxylate. The analogous difluoro system (CF₂XCOOH/CF₂X^–/CF₂) exhibits similar dissociative behavior. All experimental BDEs are in very good agreement with MP4/aug-cc-pVTZ calculations