Furo[3,4-b]benzofurans: synthesis and reactions

Starting with coumarin (1) furo[3,4-b]benzofuran 4 was synthesized using th e Hamaguchi-Ibata methodology. Intermolecular Diels-Alder reactions provide compounds 5-8. In a [4+3] cycloaddition reaction with oxyallyl compound 9 was obtained. The C-annulated furans 16a (in situ) and 16b have been prepar ed by a similar methodology starting with 10a,b. In an intramolecular Diels -Alder reaction compounds 17a,b were obtained. Computational studies concer ning the reactivity of furo[3,4-b]benzofurans in inter- and intramolecular Diels-Alder reactions using both semiempirical (AM1, PM3) and density funct ional theoretical methods (B3LYP/6-31G*) are reported.