Benzoyl azide isocyanates

Isocyanate Benzoyl Azide. See 2 Azido-formylphenylisocyanate in Vol 1, p A638-R... 

Azidofor my I phony I isocyanate (2-Isocyanate Benzoyl Azide), OC N-CONj, mw 188.15, N 29.78% Needles (from benz), mp 60° (dec) on careful heating explodes violently on rapid heating or on impact. It can be prepd by heating phthalic acid diazide in benz... 

In the presence of gallium chloride, aluminum bromide, aluminum chloride, and ferric chloride, benzoyl azide is decomposed according to eq 2. Here complex formation is very fast, and the decomposition of the complex is the ratedetermining step. The halides do not complex with the phenyl isocyanate formed and, as a consequence, they are not consumed in the reaction. As long as benzoyl azide is in excess, the concentration of the complex is equal to the halide concentration and remains constant. The experimentally determined pseudo-zero-order rate constant depends therefore upon the first power of the initial halide concentration. When, however, the reaction is at a stage where the azide is no longer in excess, the rate of the reaction becomes first order with respect to benzoyl azide and zero order with respect to halide. PhCONj + AlBr, -r - PhCONrAlBr, r+-... 

Benzoyl nitrene 247 (R = Ph) generated by photolysis of benzoyl azide in the presence of carbonyl compounds affords 1,4,2-dioxazolines 248-251 (Scheme 34). Moderate yields are obtained upon irradiation at 254 nm, while better yields are obtained upon irradiation at 365 nm in the presence of a sensitizer, such as Michler s ketone, which diminishes the photo-Curtius side reaction of acylnitrene to isocyanate. With ethoxycarbonylnitrene 247 (R=—OEt) and acetone, compounds 251 and 252 are obtained the latter is possibly formed from acetone and the dipolar intermediate 252 <1995T7181>. In another report on reactions of chiral aroylnitrene 254, the obtained dioxazolines 255 do not show any diastereoselectivity, although the presence of a chiral auxiliary in the ortfe-position ensures its vicinity to the reaction center (Scheme 35) <2001S1125>. 

Accordingly, cycloaddition reactions can be carried out in solvents such as alkanes, cycloalkanes and acetonitrile. The insertion reaction into the O-H-bond of alcohols is, in every case, faster than the cycloaddition reaction. Furthermore, 100% production of isocyanate was observed upon irradiation of benzoyl azide in dichloromethane solution, however, nitrenes that can be trapped by compounds with double bonds are also formed in this solvent [21]. 

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. 

Comprehensive studies of the photochemistry of 2-naph-thoyl and substituted benzoyl azides were undertaken to determine the multiplicity of the ground state of aroylni-trenes. Irradiation (254 nm) of 2-naphthoyl azide (26) in cyclohexane at room temperature produces N-cyclo-hexyl-2-naphthamide (27, -45%), 2-naphthyl isocyanate (28, -50%), and a trace (<1%) of 2-naphthamide (29). 

In order to determine experimentally the multiplicity and the structure of the lowest state of benzoylnitrene (25), a study of the photochemistry of benzoyl azide (24) was performed in an Ar matrix at 12 K. The formation of two species was observed upon exposure of 24 to 254 nm light. One of these species has an IR spectrum, which is consistent with that expected for phenyl isocyanate (45). The IR and UV spectrum of the second intermediate are in very good agreement with the calculated spectra of singlet nitrene in the A state (25). This intermediate undergoes isomerization to isocyanate (45) upon further exposure of the sample to 313-nm light. 

In 2012, Grushin s team developed a palladium-catalyzed carbonylative coupling of aryl iodides with sodium azide [103]. This catalytic reaction occurs smoothly at temperatures as low as 25-50 °C and 1 bar to cleanly produce aroyl azides from the corresponding aryl iodides, CO and NaNs (Scheme 4.52). The reaction exhibits high-functional group tolerance and can also be conveniently used for one-pot, two-step procedures furnishing primary benzamides, imino-phosphoranes, isocyanates, and ureas in high yield without isolation of the primary benzoyl azide product. 

Other types of bonds undergo sonolysis, for instance the nitrogen-nitrogen bond of an azido group. The Curtius rearrangement of benzoyl azide is probably one of the first attempts to use sonication in an organic reaction. 3 phenyl isocyanate is... 

More recent matrix isolation studies on benzoyl nitrene, however, did show conversion to the isocyanate. Calculations show that the acyl nitrene has oxazirene (108) character and that this 0-N interaction stabilizes the singlet state of the nitrene. Interestingly, a reexamination of benzoyl nitrene, trapped in an argon matrix and irradiated at 308 nm, revealed that in addition to phenyl isocyanate, a small amoimt of phenyl cyanate (110) was formed. Direct irradiation of benzoyl azide (254 nm) also generated the... 

The structures of donor-acceptor complexes of iyn-benzoyl azide, its 2-methyl- and 2,6-dimethyl-substituted derivatives with BF3, AICI3, and SbCls, and the transition states of the rearrangement into isocyanates have been reported by computational methods. The reaction of donor-substituted alkenes with a-diazo-a-nitro ethyl acetate under Rh catalysis have been reported which show that the nitro group is inserted forming cyclic nitronates, whereas the ester moiety was not incorporated into the ring system (Scheme 198). ... 

In hot ethanol, benzoyl azide was converted to ethyl A-phenylcarbamate (1894). This Curtius rearrangement was recognized by its discoverer as a general method of degrading carboxylic acids to amines, whereas the intermediacy of isocyanates escaped him. 

An in situ AB2 monomer having an isocyanate group, and two hydroxyl groups was prepared by thermal decomposition of 3,5-dihydroxy benzoyl azide... 

The Curtius rearrangement also occurs in the direct photolysis of acylazides, but additional products have been isolated and have been shown to arise from typical nitrene reactions . For example, Horner et have trapped benzoyl nitrene with a variety of scavengers. Similarly to the Wolff rearrangement (vide infra) it has been shown ° that the Curtius rearrangement occius via a singlet intermediate this intermediate can be a nitrene or an excited azide molecule in which a concerted decomposition leads to isocyanate derivatives. This reaction could occur in competition with nitrene formation or, alternatively, originate from a vibrationally-excited ground state azide molecule. 

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