Acyl azides chemistry

Photolysis of alkyl azides bearing pendant aryl groups does not lead to intramolecular trapping of a nitrene by the aryl group. However, intramolecular capture of the putative nitrene is observed upon pyrolysis of the azide precursor. These observations convinced Kyba and Abramovitch" ° that 1,2-migration is concerted with loss of nitrogen from the excited state of the azide, but that a free singlet nitrene is formed upon thermal decomposition. The chemistry of acyl azides will be shown later to exhibit the opposite pattern. 

The literature contains reviews of the chemistry of org azides (Refs 5 11). Smith (Ref 8) has reported on the acyl azides,... 

Conventional chemistry converted carbinol 277 into acyl azide 278, which was treated under Curtius rearrangement conditions to obtain either amine 279 or urea derivative 280, the respective precursors of guanine derivative 281 and thymidine analogue 282. 

J. Lutz, H.-J. Musiol, L. Moroder, Acyl azides. In M. Goodman, F. Arthur, L. Moroder, and C. Toniolo (eds.). Synthesis of Peptides and Peptidomimetics, Houben-Weyl Methods of Organic Chemistry, E 22a, Stuttgart George Thieme Verlag, 2002, pp. 427-441. 

Other organo-phosphorous reagents are based on the mixed carboxylic-phosphoric or phosphinic anhydrides. Initially used to convert carboxylic acids into acyl azides, DPPA 12 has been introduced as a one-pot coupling reagent for peptide chemistry (32), and it was adapted later to solid-phase chemistry (81). The driving force of these reactions is the formation of the phosphoric or phosphinic acids and their salts. Later DPP-Cl 49 (82) and FDPP 50 were introduced. FDPP 50 has been used successfully in macro cyclizations (83). Examples of... 

The preparation of acyl azides has received considerable attention due to the value of these compounds as synthetic intermediates. In the Gurtius rearrangement for example, acyl azides arc converted into isocyanates, urethans, ureas and amines and this aspect of the chemistry of acyl azides is considered in detail in a later chapter. The use of acyl azides in peptide synthesis has increased the scope of general... 

As demonstrated above, azidoformates, which, like the very similar carbamoyl azides (30 equation 33),"9, 20, 50 pjay an important role in peptide chemistry and as nitrene precursors," can be generated in the usual way. TTieir thermal stability is generally higher than that of alkanoyl and aroyl azides. The tendency of acyl azides to form 1,2,3,4-oxatriazoles in a cyclization process is extremely low. In contrast to this thioacyl azides, which are only generated on treatment of thioxohydrazides with nitrous acid, seem to be only very short-lived intermediates, which immediately form 1,2,3,4-thiatriazoles as stable end products. 

Activation of the carboxylic acid as the acyl chloride permits direct reaction with azide anion to form the acyl azide substrates for Curtius rearrangement. Sodium azide is commonly used, and the reaction has been used on the process chemistry scale for the synthesis of benzyl-A-vinyl carbamate. Acryloyl chloride was combined with sodium azide in a biphasic system with phase-transfer catalysis (PTC), providing acyl azide 25. Upon heating, Curtius rearrangement provided vinyl isocyanate, which was distilled directly into benzyl alcohol containing phenothiazine (27) to inhibit polymerization of 26 and triethylamine to catalyze addition of the alcohol to the isocyanate. The vinyl carbamate product 28 was isolated by crystallization. As the autiior clearly pointed out, preparation and reaction of acyl azides, particularly on large scales, require appropriate safety precautions. 

Vogel has applied his naked sugar chemistry to the synthesis of 5-C-methyl-nifo-nojirimycin (60), and its 6-deoxy-analogue, from the bicyclic lactone (58) derived from a chiral 7-oxanorbomane (Scheme 17). The amino-group was introduced by Curtius rearrangement of the acyl azide (59). ... 

Asymmetric synthesis of unnatural j8-amino acids derivatives based on azide chemistry is known. Enantioselective desymmetrization of mera-anhydride 293 mediated by cinchona alkaloids gives optically active monomethylester 294. This compound was converted into the acyl azide, which underwent Curtius degradation followed by alcoholysis of the intermediate isocyanate affording 8-amino acid derivative 295 in high enantiomeric excess. The authors observed that Grubbs catalyst was able to polymerize norbomene-type monomer 295 affording the corresponding polymer 296 in quantitative yield (Scheme 3.45). 

Castelhano et al. described the solid-phase synthesis of quinazoline-2,4-diones 313 based on the chemistry of acyl azides. Phthalic acid was immobilized on a PEG4-PS resin and converted into acyl azide 310 with DPPA and triethylamine in toluene. Curtius rearrangement, followed by reaction with a primary amine and subsequent cyclocleavage with K2CO3 gave quinazoline-2,4-diones 313 in good yield (Scheme 3.48). 

The importance of reactions with complex, metal hydrides in carbohydrate chemistry is well documented by a vast number of publications that deal mainly with reduction of carbonyl groups, N- and O-acyl functions, lactones, azides, and epoxides, as well as with reactions of sulfonic esters. With rare exceptions, lithium aluminum hydride and lithium, sodium, or potassium borohydride are the... 

Ar-Acyl oxy- A -a 1 k oxyamides have been found to undergo SN2 reactions with a number of organic and inorganic nucleophiles including anilines, thiols, hydroxide and azide anions. Reaction products from all of these processes are themselves reactive anomeric amides and outcomes have uncovered novel chemistry of this unusual class of compounds. 

These form derivatives with carbonyl compounds and can be acylated, sulfonylated, eliminated by mild oxidation [e.g. (762 Y = NHNH2) + CuS04 + AcOH — (762 Y = H)]. They are converted by nitrous acid into azides as in benzenoid chemistry. 

Demko and Sharpless proved the efficiency of this version of the click chemistry approach by successful syntheses of 5-acyltetrazoles from azides and acyl cyanides followed by their further functionalization. They used />-nitrophenyl cyanoformate to bring together an azide and nucleophiles in a one-pot process to give in high yield disubstituted acyltetrazoles, such as 544 and 545, via 1-substituted 5-acyltetrazole 543 (Scheme 79) <2002AGE2113>. 

---