Annelated furans. VI. Diels-Alder addition to 3-Methoxy-2-vinylbenzofurans

Abstract

The Diels-Alder addition of 3-methoxy-2-vinylbenzofurans to acetylenic dienophiles has been shown to be accompanied by elimination of methanol, thus affording a direct route to polyfunctional dibenzofurans. Ethylenic dienophiles also reacted but the nature of the product varied with the dienophile: thus tetra-cyanoethylene and 2- isopropenyl-3-methoxybenzofuran (17) gave the simple 1 : 1 adduct, 1,1,2,2-tetracyano-11-methoxy-4-methyl-1,2,3,11-tetrahydrodibenzofuran (26), while addition of maleic anhydride to (17) was accompanied by elimination of methanol to form the 1,2-dihydrodibenzofuran, 4-methyl- 1,2-dihydrodibenzofuran-1,2-dicarboxylic acid anhydride (27).     The addition of p-benzoquinone and 1,4-naphthaquinone to (17) gave the polycyclic quinones, 6-methyl-1,4-dioxo-1,4- dihydrobenzo[b]naphtho[1,2-d]furan (28) and 7-methyl-5,13-dioxo-5,13- dihydrobenzo[b]anthra[1,2-d]furan (29) respectively.     The methylation of enolic 3-hydroxybenzofurans has also been studied.