Development of synthetic method for constructing benzo-annulated framework by utilizing arynes

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New method for synthesizing benzo-annulated heterocycles such as coumarins and acridanes based on the highly electrophilic character of arynes has been developed. The key intermediates in these reactions are ortho-quinoid species (ortho-quinone methide, ortho-azaxylylene) arising from formal [2+2] cycloaddition between arynes and carbon-heteroatom double bonds (dimethylformamide, imine). Subsequent [4+2] cycloaddition between the resulting ortho-quinoid species and ester enolates or second arynes provides the final products.