Benzyne with azirines

Cycloaddition reactions of the C(3)=N bond of azirines are common (Scheme 45) <71AHC(13)45, B-83MI 101-03,84CHEC-I(7)47>. Azirines can participate in [4 + 2] cycloadditions with dienes including cyclopentadienones, isobenzofurans, triazines, and tetrazines. They also participate in 1,3-dipolar cycloadditions with azomethine ylides, nitrile oxides, mesoionic compounds, and diazomethane. Cycloadditions with heterocumulenes, benzyne, and carbenes are known. Azirines also participate in other pericyclic reactions, such as ene reactions. 

Diphenyl-l-azirine (29) and benzyne yield the 1 1 adduct 31 (50%) and 1 2 adduct 32 (14%).34 The formation of these indoles can be explained by assuming 1,2-cycloaddition of benzyne, reorganization of the strained intermediate 30, and some N-phenylation of 31 by further reaction with benzyne. 

Fluoride-ion-mediated generation ofbenzyne from silylaryl triflates (41) [20] is mild and excellent in chemical yields andsoithasbeen employed for a variety of electrophilic (42) [21 ], nucleophilic (43) [22], and cycloaddition reactions [23] (Scheme 3.26). N-Phenylations of sulfonamides (44), amines (45) [24], azirines [25], oxazoles [26], pyrroles [27], and imidazoles [28] with benzyne from 41 are also known. 

---