Carbamoyl azides mechanism

As for the acetyl phosphate monoanion, a metaphosphate mechanism has also been proposed 78) for the carbamoyl phosphate monoanion 119. Once again, an intramolecular proton transfer to the carbonyl group is feasible. The dianion likewise decomposes in a unimolecular reaction but not with spontaneous formation of POf as does the acetyl phosphate dianion, but to HPOj and cyanic acid. Support for this mechanism comes from isotopic labeling proof of C—O bond cleavage and from the formation of carbamoyl azide in the presence of azide ions. 

Ketene also appears to react with hydrazoic acid according to the general mechanism outlined in equation (88). Carbamoyl azides are produced and it is thought that the reaction proceeds by initial protonation and subsequent attack by azide ion to afford an acyl azide further reaction of the derived isocyanate would then lead to the observed product (equation 90). 

Moreover, Bols et al. developed another methodology for the synthesis of carbamoyl azides from aldehydes by treatment with iodine azide at reflux in acetonitrile [41]. The carbamoyl azides are obtained in 70-97 % yield from the aliphatic and aromatic aldehydes (Scheme 5.4). When the reaction of phenyl-propanal with IN3 at 25 °C was performed in the presence of the radical trap, no acyl azide was observed, which was taken as support for a radical reaction mechanism. The mechanism shown in Scheme 5.6 is proposed for the reaction. Iodine radicals are formed by homolysis of the weak iodine-azide bond, abstracting the aldehyde hydrogen atom. The resulting carbon-centered radical reacts with iodine azide to produce an acyl azide. The following Cuitius rearrangement provides carbamoyl azides. 

In 2003, Bols and co-workers described that the reagent IN3 can easily transform the aldehydes into the acyl azides under mild conditions (Scheme 6.22a) [76]. Furthermore, they demonstrated that the synthesis of carbamoyl azides could be realized at reflux by combining the aldehyde C-H bond azidation and flie Cuilius rearrangement in a one-pot protocol (Scheme 6.22b). A possible radical mechanism were proposed for this transformation (Scheme 6.22c). The weak I-N3 bond homolysis can initiate the chain reaction. The generated iodine radical abstracts an aldehyde hydrogen atom from the substrates to produce the acyl radical A. The acyl radical A reacts with IN3 to afford the acyl azides and iodine radical, thereby sustaining the radical chain. 

Ar-(cr-Chlorobenzylidene)carbamoyl chloride (241 R = Cl) reacted with sodium azide in glyme to give the fused oxadiazole 242 in 52% yield, in addition to other products.328 The mechanism of this reaction is uncertain, but it is thought to involve the intermediacy of 241 (R = N3) and the triazolone 243. 

Methyl 2-oxo-l-indanecarboxylate (133) with p-nitrobenzenesulfonyl azide gave methyl 2-[A -(p-nitrobenzenesulfonyl)carbamoyl]-3,4-dihydro-l-phtha-lazinecarboxylate (134) (or tautomer) (EtsN, THF, 0°C 20" C, 1 h crude) and thence methyl 4-[A -(p-nitrobenzenesulfonyl)carbamoyl]-l-phthalazine-carboxylate (135) (tetrachloro-l,2-benzoquinone, PhH, reflux, 10 min %) stmcture (135) was confirmed by X-ray analysis and a synthetic mechanism... 

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