Studies on the synthesis of xanthones .10. Synthesis of furanoxanthones

The Claisen rearrangement of 3-(3-phenyl-2-propenyloxy) xanthone (1) gave 3-hydroxy-4-(1-phenyl-2-propenyl) xanthone (2) and trans-2,3-dihydro-2-methyl-3-phenyl-(9H)-furo (3,2-b) xanthone (3) which on dehydrogenation with Pd/C furnished 2-methyl-3-phenyl-(9H)-furo (3,2-b) xanthone (4). 2,4-Dimethyl-3-phenyl-(11 H)-furo (3,2-d) xanthone (8) and 2-methyl-3-phenyl-(4H) furo (2,3-d) xanthone (11) were similarly synthesised from 1-(3-phenyl-2-propenyloxy)-3-methylxanthone (5) and 2-(3-phenyl-2-propenyloxy) xanthone (9). The stereochemistry of the intermediate 2,3-disubstituted 2,3-dihydro furanoxanthones was established by H-1 NMR spectra.