Quaternization of quinoxalines

Several different approaches have been adopted for the synthesis of pyrrolo[l,2-a]quinoxalines. Particularly useful are approaches involving cyclization reactions of o-aminophenylpyrroles. Alternative syntheses have involved the use of o-phenylenediamine, the cyclization of /3-quinoxalinylpropionic acids, quaternization of quinoxaline derivatives, as well as several other routes less amenable to classification. 

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. 

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