Singlet Photoreactivity of 3-Methyl-2-phenyl-2H-azirine

Abstract

Irradiation of 3-methyl-2-phenyl-2H-azirine (1) at 254 nm in argon matrices results in ylide 6. Similarly, laser flash photolysis (λ = 266 nm) of azirine 1 in acetonitrile yields ylide 6, which has a transient absorption with λmax at ~340 nm and a lifetime of 14 μs. Density functional theory calculations were preformed to support the characterisation of ylide 6 in solution and argon matrices. Irradiation of azirine 1 above 300 nm has previously been reported (J. Org. Chem. 2014, 79, 653) to yield triplet vinylnitrene in solution and ketenimine in cryogenic argon matrices. Thus, the photochemistry of azirine 1 is dependent on the irradiation wavelength.

Imidoylnitrenes R′C(═NR)–N, Nitrile Imines, 1H-Diazirines, and Carbodiimides: Interconversions and Rearrangements, Structures, and Energies at DFT and CASPT2 Levels of Theory

“…The diazirine lies 6.9 kcal mol –1 higher than 8c . As reported elsewhere, nitrile imine 8c can exist in both allenic and propargylic forms, and both forms ring close photochemically to 9c . The 1 H -diazirine 9c can ring-open to the imidoylnitrene 10c via transition states TS 9–10cZ and TS 9–10cE lying 18.9 and 23.2 kcal mol –1 above 8c , respectively.…”

“…As reported elsewhere, nitrile imine 8c can exist in both allenic and propargylic forms, and both forms ring close photochemically to 9c. 21 The 1H-diazirine 9c can ring-open to the imidoylnitrene 10c via transition states TS 9−10cZ and TS 9−10cE lying 18.9 and 23.2 kcal mol −1 above 8c, respectively. Again, because of steric interaction with the phenyl group in the E conformer, the Z conformer 10cZ and the corresponding transition state are of the lower energy.…”

“…In contrast with the acylnitrenes, vinylnitrenes 3 have triplet ground states, examples of which have recently have been observed directly by ESR and UV−vis spectrocopy. 18,19 The singlet vinylnitrenes undergo cyclization to 2H-azirines 5 20,21 and rearrangement to ketenimines 4 (Scheme 1). 22 There is much less direct knowledge about the chemistry of imidoylnitrenes 10, but these species are postulated as the crucial but so far unobserved links between nitrile imines 8 and carbodiimides 11 (Scheme 2).…”

“…In contrast with the acylnitrenes, vinylnitrenes 3 have triplet ground states, examples of which have recently have been observed directly by ESR and UV–vis spectrocopy. , The singlet vinylnitrenes undergo cyclization to 2 H -azirines 5 , and rearrangement to ketenimines 4 (Scheme ). …”

7th Heron Island Conference on Reactive Intermediates and Unusual Molecules

“…meeting covering a wide range of topics, including phenol-arene cross-coupling (König et al), [1] oxaphosphirane complex (Streubel et al), [2] HNC mediated Mukaiyama reactions (Lupton and Nguyen), [3] hydroxyl radicals (Williams et al), [4] triplet excited states of ketones (Bucher), [5] aziridination of dicarbonyl compounds (Chan et al), [6] copper iodide complexes of macrocycles (Baranová et al), [7] electric field effects on radical stability (Coote and Gryn'ova), [8] photoreactivity of azirine (Gudmundsdottir et al), [9] carbocation cyclization/rearrangement cascades (Tantillo and Hong), [10] cleavage of electron- deficient acetylenes (Alabugin et al), [11] and a review of the HERON reaction (HEteroatom Rearrangement On Nitrogen) (Glover). [12] The next Heron Island Conference will take place in early July 2019.…”