Benzodipyrans. Part V. Synthesis of a linear dihydrobenzodipyrandione isolated from dill and of other similar benzodipyrandiones

Abstract

7,8-Dihydro-8,8-dimethylbenzo[1,2-b:5,4-b′]dipyran-2,6-dione (IX) has been synthesised from 3,4-dihydro-7-hydroxycoumarin in three steps. Application of the same reaction sequence to 3,4-dihydro-5,7-dihydroxycoumarin yielded the angular isomer (XII) of the naturally occurring clausenin. Bromination of 7-hydroxy-2,2-dimethylchroman-4-one gave its 8-bromo-derivative with N-bromosuccinimide and its 6-bromo-derivative with bromine–chloroform. The former failed to undergo Pechmann condensation with malic acid but the latter condensed readily.