Bridged Xanthenes. I. An Intermolecular Cycloaddition Route

Abstract
Condensation of o-hydroxybenzyl alcohol (4) with 1,3-cyclohexanedione (7) in hexamethylphosphoramide gives 3,4-dihydro-l(2H)-xantnenone (9). Treatment of the tosylhydrazone of 9 with methyllithium gives 3,4-dihydroxanthene (12), which undergoes Diels–Alder reactions with dimethyl acetylenedicarboxylate and propiolonitrile to give the bridged xanthenes 15 and 17, respectively. Condensation of o-hydroxybenzyl alcohol (4) with 4-carboxamido-1,3-cyclohexanedione (29) and 4-carbomethoxy-1,3-cyclohexanedione (38) gives 2-carboxamido-(30) and 2-carbomethoxy-3,4-dihydro-l(2H)-xanthenone (39), respectively.

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