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Photo‐decarbonylation of β‐styryl isocyanates
Author(s) -
Boyer J. H.,
Mikol G. J.
Publication year - 1972
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570090624
Subject(s) - chemistry , isocyanic acid , isocyanate , benzonitrile , nitrene , azirine , ketenimine , medicinal chemistry , nitrile , decarbonylation , photochemistry , organic chemistry , catalysis , ring (chemistry) , polyurethane
β‐Styryl isocyanate (1, R H) and its β‐methyl‐ (1, R CH 3 ) and β‐phenyl‐ (1, R C 6 H 5 ) 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 CH 3 ) from 1 , (R CH 3 ) provided diagnostic evidence for styryl nitrene ( 2a ) intermediates. The formation of both phenylacetonitrile ( 5 , R H) and α‐phenylpropio‐nitrile ( 5 , R CH 3 ) was assigned to an initial rearrangement of the residue, C 8 H 6 (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 C 6 H 5 ) 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, C 17 H 14 N 2 O and C 12 H 14 N 2 O, were obtained from 1 , (R CH 3 ).