3,3'-Dihydro-4,4'-dicumarin;4,4'-dimer of chroman-2-one;3,4,3',4'-tetrahydro-[4,4']bichromenyl-2,2'-dione;Isobisdihydrocoumarin;Bisdihydrocoumarin;4-(2-Oxo-3,4-dihydrochromen-4-yl)-3,4-dihydrochromen-2-one
Irradiation (lambda >300 net) of coumarin-3-carboxylic acid gives the decarboxylated 4,4'-dimer of chroman-2-one, the structure of which is quite different from that of [pi2s+pi2s] cycloaddition dither as is observed in the past in the photoreaction of coumarin or some of its derivatives. (C) 2002 Elsevier Science Ltd. All rights reserved.