Dibenzopyranone formation

Dibenzo-/ -dioxins 1086 Dibenzodioxocines 1308, 1309, 1311 Dibenzofurans, formation of 1289, 1291 Dibenzopyranones, formation of 1257 Dibenzoylmethane enol, IR spectrum of 382... 

Formation of the isochroman system is considered to trigger the synthesis of the dibenzopyran (17, X = H2) by the acid catalysed cyclisation of c/s-enediynes (16, X = H2). In a similar manner, the carboxyl function in (16, X = O) promotes cylisation to a dihydropyranone derivative which is followed by a Myers cycloaromatisation to the dibenzopyranone (17, X = O) (95TL9165). 

Recently, an example of intramolecular formation of Ar-Ar bonds has been reported, consisting in the preparation of dibenzopyranone derivatives by a highly selective, Pdfacacf /CuCl-mediated tandem reaction [70]. Substituted 2-nitrobenzoic acids and methyl 2-bromo benzoate derivatives are used as starting materials. 

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