The photochemistry of acyl azides — IX. Direct and sensitized photolytic generation of acylnitrenes for cycloaddition reactions

Visible light C–H amidation of heteroarenes with benzoyl azides

“…Sensitive groups like cyano or ester moieties are well tolerated (compound 3e and 3f respectively). It was reported that benzoyl azides react under light irradiation with cyanide groups to give oxadiazole, 11 , 12 but in our conditions we only obtained the desired product in 63% yield. Product 3g bearing a chlorine atom allows for subsequent functionalization by transition metal mediated cross-coupling, 13 and the use of heteroaryl acyl azide 1h yields diheteroaryl amide 3h in 49%.…”

“… 17 In the presence of hydrogen donors benzamides are obtained and the reaction with double bonds yields aziridines or oxazolines. 11 , 12 , 18 The ratio between isocyanate and nitrene formation from the excited benzoyl azide is reported to be independent of the presence and the amount of alkenes as trapping reagent; 19 the photophysical mechanism of sensitized and direct benzoyl azide decomposition has been investigated in detail. 20 Some recent examples using azides in photocatalyzed reactions suggest a nitrene intermediate from single electron transfer or by sensitization.…”

“…Benzoyl azides have been used previously in transition metal catalysis, but the reaction requires the presence of a directing group. 10 Exposed to UV irradiation 11 benzoyl azides give oxazolines, dioxazoles or aziridines, but no conversion of heterocycles or formal amidation was observed under these conditions. 12 We activate benzoyl azides using visible light and a photocatalyst allowing a direct C–H amidation of heteroarenes.…”

Intermolecular and Selective Synthesis of 2,4,5‐Trisubstituted Oxazoles by a Gold‐Catalyzed Formal [3+2] Cycloaddition

“…While robust pyridine-Naminides, such as 1 a (YÀZ = NÀC=O), are established as 1,3-C,N dipoles incorporating the pyridine group, [10] an alternate reactivity as an N-nucleophilic 1,3-N,O-dipole equivalent would emerge under the proposed catalytic regime. [14,15] A copper-catalyzed cycloaddition-fragmentation-cyclization cascade affords 2,5-disubstituted oxazoles from terminal alkynes and acyl azides. Single-crystal X-ray diffraction confirmed the structure of 3 aa and hence the regioselectivity of the intermolecular cycloaddition.…”

Intermolecular and Selective Synthesis of 2,4,5‐Trisubstituted Oxazoles by a Gold‐Catalyzed Formal [3+2] Cycloaddition

“…[13] This is seemingly due to poor chemoselectivity in the formation and application of the required 1,3-N,O-dipole equivalent, acyl nitrenes, for instance by thermal or photochemical decomposition of acyl azides in the presence of alkynes. [14,15] A copper-catalyzed cycloaddition-fragmentation-cyclization cascade affords 2,5-disubstituted oxazoles from terminal alkynes and acyl azides. [16] Similarly convergent one-step or one-pot methods to prepare functionalized 1,3oxazoles are rare, [8] and often require the use of highly reactive species with consequent structural limitations.…”