Phenyl isocyanate, photolysis

The photolysis of the meso-ionic 1,4-diphenyl-l,2,4-triazol-3-one (200, R = R = Ph, R = H) was stated to yield phenyl isocyanate (13%), 7V,iV -diphenylurea (23%), and the bicyclic compound 215 (49%). These results were interpreted in terms of the fragmentation of the photo-intermediate 213 yielding the iV-phenyldiazirine (214). A later publication by the same group reports different results. Photolysis of meso-ionic 1,4-diphenyl-l,2,4-triazol-3-one (200, R = R = Ph, R = H) was stated to yield phenylisocyanate and the bicyclic compound 215. Later studies have shown that the bicyclic compound... 

The key intermediate of Scheme 1 is singlet phenylnitrene the only intermediate which in 1992 had not been detected directly or chemically intercepted in the parent system. In 1997 our group" " and the Wirz group, simultaneously reported that laser flash photolysis of phenyl azide or phenyl isocyanate 5 produces a previously undetected transient with = 350 nm and a lifetime of ns at ambient temperature. 

Photolysis of acid azides, yielding AT-heterocyclic compounds, has been reported, e.g., the formation of benzoxazolone (CCXXXIX) via the photolysis of salicyclic acid azide (CCXXXVIII). It is suggested that the photolysis of benzoylazide (CCXL) proceeds via the intermediate radical (CCXLI) which rearranges to phenyl isocyanate (CCXLII). 

Quinoxaline 1-oxide (209) reacts with phenyl isocyanate to give 2-anilinoquinoxaline (210) together with 1,3-diphenyl-l-(2-quinoxalinyl)-urea (211) and cyclized oxidation product of the urea 212.215 2-Quinoxalinone 4-oxide (205) and its 1-methyl derivative undergo addition reactions, e.g., with phenyl isocyanate and benzyne to give compounds 214 and 216, respectively.216 These reactions are formulated as proceeding via the intermediate cycloadducts 213 and 215. Compound 216 has also been obtained by photolysis of 3-(o-hydroxy-phenyl)quinoxaline 1-oxide.51 1,3-Dipolar cycloaddition of quinoxaline... 

Franz and Black539 have studied the thermolysis and photolysis of l,3,4-oxathiazol-2-one (l).530 This compound is thermally labile and yields benzonitrile and sulfur instead of the expected phenyl isocyanate and carbonyl sulfide. It is probable that benzonitrile sulfide (3) is an intermediate and this appears to be confirmed by formation of the adduct 4 in 90% yield when 1 is heated with 2 moles of DMAD at 130° in chlorobenzene. Heating a mixture of benzonitrile and sulfur with DMAD gave tetramethyl thiophenetetracarboxylate (6), also obtained without the nitrile. The formation of the isomeric isothiazoles 7 and 8 from 1 and EP531 is similar to the production of the corresponding... 

Sydnones can be regarded as cyclic azomethine imines and as such they undergo thermal cycloaddition reactions with a range of dipolarophiles. Thus, reaction with phenyl isocyanate converts 401 into 1,2,4-triazole 402. On photolysis, 3,4-diarylsydnones lose carbon dioxide and give nitrile imines, which can also be intercepted by dipolarophiles. Thermal reactions with acetylenic dipolarophiles lead to the formation of pyrazoles (Scheme 88) however, these reactions are rarely completely regioselective with unsymmetrical alkynes, e.g., <2000BKC761, 2000TL1687>. 

Eibler and Sauer15 8 demonstrated with the aid of competition experiments that the same intermediate, in all likelihood the benzoylnitrene, was formed by photolysis of 110-112 (Eq. 34). Phenyl isocyanate was formed both thermally and photolytically from all three precursors, but no evidence for a nitrene was obtained under thermal conditions. 

Apparently, benzoylnitrene is formed in the thermolysis (120 C) of 0,jV-bis(trimethyl-silyljbenzocarboximidicacid and trapped with cyclohexene to give, V-(3-cyclohexenyl)benzamide (10/ ,) together with phenyl isocyanate.168 Benzoylnitrene is apparently also formed by sul-filimine photolysis and trapped with cyclohexene to give A/-benzoyl-7-azabicyclo[4.1.0]heptane (15.6%). 55 ... 

Reynolds, Van Allen and Borden 31> made use of the photochemical rearrangement of benzoyl azides to phenyl isocyanates to conduct a photopolycondensation. By incorporation of a group, reactive with isocyanates, such as amino, into the same molecule, photolysis led to formation of a polyurea structure. 

The photolysis of benzoyl azide (PhCON3) has been investigated by means of matrix isolation, time-resolved IR spectroscopy, and computations at various levels of theory.In argon at 12 K, formation of two species was observed. One of these was phenyl isocyanate (PhCNO), while the other had an IR spectrum consistent with the predicted spectrum of the reactive singlet species PhCON, which appears to have a structure intermediate between that of a carbonyl nitrene and an oxazirene. Analogous observations were also made for 4-acetyl-benzoyl azide. Time-resolved IR spectroscopy on the nanosecond time scale provided additional evidence for the singlet ground state of benzoylnitrene. 

In 1968 Porter and Ward [87] studied the gas phase flash photolysis of ortho-chloro aniline, ortho-bromo aniline and phenyl isocyanate and observed a strong new transient absorption with a half-life of ss 100 /is. A series of well resolved vibrational bands were observed between 370.629 and 345.310 nm. The most intense band was observed at 368.307 nm. Porter attributed this band system to triplet phenyl nitrene. The nitrene can of course be easily formed from phenyl isocyanate by extrusion of carbon monoxide. 

This assignment was indicated by the observation of the C = N characteristic vibration, the predicted 15N isotope shift to the nitrile vibrational frequency and confirmed by the independent generation of radical 7 by photolysis of cyanocyclopentadiene in the jet expansion. It is now clear that the spectrum reported by Porter and Ward [87] is that of cyanocyclopentadienyl radical and not that of triplet phenyl nitrene. To our knowledge triplet phenyl nitrene has never been spectroscopically detected in the gas phase. We assume that gas phase photolysis of phenyl isocyanate or phenyl azide produces singlet phenyl nitrene which is born with sufficient excess vibrational energy to drive the known rearrangement to cyanocyclopentadiene... 

Irradiation of a benzene solution of 5-phenyl Af-benzoylformyl-A-p-tolylthiocar-bamate 48a (Scheme 23) gave 5-phenyl-5-phenylthio-3-p-tolyloxazolidine-2,4-dione 49a in 61% yield accompanied by oxazolidine-2,4-dione dimer (15%), p-tolyl isocyanate (22%), and diphenyl disulfide [29]. Photolysis of 48a in the solid state gave oxazolidine-2,4-dione 49a in 96% yield. For the N-methyl derivative, 48b, compared to the solution photochemistry in which only 8% of oxazolidinedi-one 49b was obtained with a complex mixture, radical cyclization proceeds selectively to give oxazolidinedione in 75% yield in the solid state. Whereas N-p-tolyl and A-methyl derivatives, 48a and 48b, formed achiral crystals, the N-benzyl derivative 48c crystallized in chiral space group P2. Photolysis of the chiral... 

Diazocines 54 (R = H, Me) were synthesized by treating phenyl and o-tolyl isocyanate with aluminum chloride (51DOK1073). A Michael addition was involved in the reaction of benzylideneacetone with 1,3-diamino-propane to yield diazocine 161 (71JCS(D)372). Photolysis of diphenylaryl-... 

A related ring closure with formation of 3-phenyl isocarbostyril 226 is observed in the photolysis of /3-styril isocyanate 225. ... 

---