C-AZIDODIAZIRINES IN THE S(RN)1 REACTION OF AZIDE ION WITH ARYLCHLORODIAZIRINES - FURTHER INSIGHTS INTO REACTION-MECHANISM

Mixtures of arylchlorodiazirines and sodium azide in DMSO form visible charge transfer complexes. Irradiation of these solutions with fluore scent room light leads to S(RN)1 displacement of chloride and the tran sient formation of C-azidodiazirines. Relative reactivity studies (usi ng competition experiments) show that nitro-substituted arylchlorodiaz irines are substantially more reactive than other arylchlorodiazirines . This is attributed to facile electron transfer in the propagation cy cle, involving the nitro-substituted aromatic ring. C-Azidodiazirines can be isolated in solution and spectroscopically characterized when t he S(RN)1 reaction is initiated by addition of catalytic amounts of th e sodium salt of 2-nitropropane. These azidodiazirines readily decompo se at room temperature by first order processes to give molecular nitr ogen and benzonitriles. Solvent and substituent effects on decompositi on rates are minimal. Computational studies on potential intermediate carbenes in the decomposition of azidodiazirines have been carried out at the HF/6-31G level. Singlet alpha-azidocarbenes RCN3, where R = N H2, OH, F, vinyl, phenyl, and CH3, are energy minima at this computati onal level. Isodesmic calculations show that the azido group is compar able to OH in its carbene stabilizing ability. Subsequent loss of N2 f rom alpha-azidocarbenes, leading to nitriles, is a highly exothermic p rocess (126 kcal when R = vinyl and 128 kcal when R = phenyl).