Azirino quinoxalines

Carbanions of a-haloalkyl aryl sulfones, sulfonates and sulfonamides react with quinoxalines according to two general pathways vicarious nucleophilic substitution of hydrogen and/or bis-annulation to bis(azirino)quinoxaline derivatives. The charge distribution in the anionic (T-adducts and reaction conditions influence the direction of these reactions. ... 

Quaternization of quinoxaline is neatly avoided by the synthesis of the azirino[l,2-a]quinoxalines 71 from o-phenylenediamine and the dibromo ketones 70. The azirino compound apparently acts as a 1,3 dipole and undergoes addition with a variety of dipolarophiles to give fused quinox-alines containing a bridgehead nitrogen atom. " Thus the acetylene derivatives 72 give the pyrrolo derivatives 73. The yields are much improved by the use of chloranil in situ to oxidize the presumed dihydro intermediates 74. 

The fact that these reactions take place through the 1,3-dipolar intermediate 69, arising as a result of thermal cleavage of the C-C bond of the azirino[l,2-a] quinoxaline system, is favored by the formation of p,p -dinitrostilbene and 2-phenylquinoxaline (Heine and Henzel 1969) according to the following Scheme 3.22. 

Scheme 3.22 The themal cleavage of azirino[l,2-a]quinoxaline derivatives...

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