Isocyanates carbonyl azides

N-benzylaniline with phosgene, and then with sodium azide to produce carbonyl azide 52. On heating, nitrogen is evolved and a separable mixture of nitrene insertion product 53 and the desired ketoindazole 54 results. The latter reaction appears to be a Curtius-type rearrangement to produce an N-isocyanate (54a), which then cyclizes. Alkylation of the enol of 54... 

Kumar and Ramakrishnan synthesized hyperbranched polyurethanes via the in-situ generation of 3,5-dihydroxyphenyl isocyanate from the corresponding carbonyl azide [98]. The degree of branching was determined as being close to 0.6 using NMR spectroscopy. The hyperbranched polyurethane was completely soluble in common organic solvents while the linear counterpart was completely insoluble. 

The pyrrole derivative of carbonyl azide 206 undergoes thermal Curtius rearrangement into isocyanate, which spontaneously cyclizes into pyrrolo-diazepinone 207 (Equation (27) (1991JHC1911)). 

Mild thermal rearrangement of the carbonyl azides 408 in 1-methylpyrrole gave l-methyl-A -(2-thiophene)-, l-methyl-iV-(2-selenophene)- and l-methyl-iV-(2-furano)-l//-pyrrole-2-carboxamides 409 in good yields, presumably involving the intermediacy of the corresponding isocyanate (Equation 97) <2000ARK58>. In this case, the successful outcome of such thermal reactions is ascribable to the pronounced acidic property of the pyrrole 2-proton. 

The photolytic decomposition of carbonyl azides produces generally, but not exclusively, isocyanates " . Lwowski has investigated this photorearrangement in pivaloyl azide He flnds an isocyanate... 

The most common thermal reaction of carbonyl azides is isocyanate formation. This reaction, known as the Cmtius rearrangement, was reported as early as 1914. 

Photolysis of carbonyl azides gives rise to two types of reactions. The photo-Curtius rearrangement proceeds to form isocyanate. In addition, bimolecidar trapping products, typical of the reactions of singlet carbonylnitrenes, are also observed. 

The yield of isocyanates, formed upon photolysis of a series of carbonyl azides (R-CO-N3, R= -butyl, aryl). 

Carbonyl azides are usually obtained from the hydrazides, although in principle they can also be prepared directly from the carbonyl chlorides and sodium azide. They are frequently used as intermediates for synthesis of isocyanates, urethanes, ureas, amines, etc., and are often used in such work without isolation. 

These azides undergo Curtius rearrangement to vinyl isocyanates, which are prone to polymerization. Where polymerization does not interfere, hydrolysis of the vinyl isocyanate provides aldehydes or ketones via the enamine. Bomylene carbonyl azide (47) yielded epicamphor (48) via the Curtius rearrangement-hydrolysis sequence. ... 

Other carboxamidation reactions involving aromatic compounds involve the generation of isocyanates from carbonyl azides. For example, thermolysis of certain carbonyl azides substituted in the a-position by vinylidene radicals, such as 220, or aryl rings undergo cyclization to the pyridones 221 or condensed pyridones . 

Also, thermolysis of a carbonyl azide attached to an oxiranering generates the isocyanate 357, which undergoes an intramolecular cycloaddition to give a 3-oxazolin-2-one 358" . ... 

Also, bis-alkylthiocarbene undergoes the [4+1] cycloaddition reaction with a suitably substituted indol isocyanate to give the [4+1] cycloadduct in 72 % yield. This approach was utilized in the total synthesis of (+) phenserin . Numerous examples of vinyl isocyanates, generated from the corresponding carbonyl azides, in the presence of bis-alkylthiocarbene precursors afford the [4+1] cycloadducts, often in high yields . ... 

The thermal rearrangement of carbonyl azides (Curtius rearrangement) giving isocyanates in quantitative yields at 60-80 °C has been known over the years and has been... 

It has been shown that the yield of isocyanates, formed upon photolysis of a series of carbonyl azides (R-CO-N3, R = -Butyl, Aryl), remains constant in the presence and in the absence of nitrene traps.For example, the yield of isocyanate 33a produced on photolysis of pivaloyl azide (R = r-Butyl, 31a) in methylene chloride (an inert solvent) is 40%. Photolysis of 31a in cyclohexene leads to a 45% yield of aziridine adduct 34a and a 41% yield of isocyanate 33a. Trapping the nitrene does not depress the yield of isocyanate. Hence, isocyanate 33a and adduct 34a cannot be derived from the same reactive intermediate, but instead the isocyanate must be formed from the excited state of the azide or from the electronically or thermally excited nitrene. 

Similar results (formation of nitrene derived products and the absence of isocyanate and products of its transformations) were obtained upon photolysis of (4-acetylphenoxy) carbonyl azide. ... 

In a reaction related to azide carbonylation, aromatic nitroso compounds also give isocyanates (equation 94). [Rh2Cl2(CO)4] (96), [RhCl(CO)2py], [RhCl(CO)(PPh3)2] (71) and [RhCl(CO)-(P(OPh)3 2] all catalyzed the reaction. Deoxygenation of the nitrosobenzene derivative was the rate determining step.448 Nitrosomethane can be similarly carbonylated.449-451... 

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>. 

---