Photo‐decarbonylation of β‐styryl isocyanates

Abstract

β‐Styryl isocyanate (1, R  H) and its β‐methyl‐ (1, R  CH3) and β‐phenyl‐ (1, R  C6H5) derivatives underwent both extensive polymerization and the loss of the elements of carbon monoxide upon irradiation at 254 nm in cyclohexane. The formation of 2,5‐diphenylpyrazine (3) and indole 4, (R  H) from 1, (R ‐ H) and 2,3‐dimethyl‐5,6‐diphenylpyrazine (6) and 2‐methylindole (4, R  CH3) from 1, (R  CH3) provided diagnostic evidence for styryl nitrene (2a) intermediates. The formation of both phenylacetonitrile (5, R  H) and α‐phenylpropio‐nitrile (5, R  CH3) was assigned to an initial rearrangement of the residue, C8H6(R)N̈: (2), into a ketenimine concerted with the elimination of carbon monoxide from 1. Isomerization then produced a nitrile. β3‐(β‐phenyl)styryl isocyanate (1, R  C6H5) gave no product requiring the intermediacy of a nitrene and/or an azirine. The formation of 2,3,4,5‐tetraphenylpyrrole (8) was assigned to a dimerization of the isocyanate concerted with or following the elimination of the elements of carbon monoxide and isocyanic acid, and the formation of 3‐phenylisocarbo‐styril (9) was assigned to a ring‐closure of the isocyanate in an excited triplet state. Each isocyanate gave stilbene and trace amounts of oxidative fragmentation into benzaldehyde and benzonitrile. Solvent participation produced benzylcyclohexane and bicyclohexyl. Two unidentified solids, C17H14N2O and C12H14N2O, were obtained from 1, (R  CH3).

Pyrolysis of benzotriazoles. Relationships between 1- and 2-vinylbenzotriazoles, α- and β-azidostyrenes, N-phenylketenimine and indole. Pitfalls in the use of pyrolysis-mass spectrometry in mechanistic studies

“…Pyrolysis of 3-phenylazirine 12 also affords indole, which suggests ring opening to the nitrene 26 (Scheme 12) [36]. Also photolyses of -styryl azide and -styryl isocyanate afford indole and phenylacetonitrile, which were ascribed to rearrangements of -styrylnitrene 26 [18,37]. was isolated in an Ar matrix at 14K and photolyzed at either 365 or 313 nm.…”