Carbocycles from Aryne Intermediates

Prior to 1960 little work had been done on reactions of heterocyclic compounds involving hetarynes, i.e. intermediates with a triple bond in the nucleus containing the hetero atom. Since then interest in hetarynes has grown and investigations in this area are developing rapidly using information available from carbocyclic aryne chemistry. Therefore, a short survey of the chemistry of arynes is presented before summarizing typical problems encountered in hetaryne chemistry. 

Arynes and heteroarynes are reactive intermediates derived formally by the removal of two adjacent hydrogens from, respectively, a carbocyclic or a heterocyclic aromatic ring. Prototypical examples are benzyne (1) and 3,4-didehydropyridine (2). Since these molecules contain a partial triple bond, they are properly regarded as -ynes and, as will be seen, undergo many reactions typical of that functionality, modified by the inherent strain caused by their nonlinearity. 

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