Efficient synthesis of furan-2-ylacetates, 7-(alkoxycarbonyl)benzofurans, and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans based on cyclization reactions of free and masked dianions: A "cyclization/dehydrogenation" strategy

A variety of furan-2-ylacetates have been prepared by dehydrogenation of monocyclic 2-alkylidene-tetrahydrofurans, which are readily available by cyclizations of open-chained 1,3-dicarbonyl dianions with 1-bromo-2-chloroethane. 5'H-[2,3']Bifuranyl-2'-ones are available based on sequential "cyclization/dehydrogenation" reactions of alpha-acetyl-gamma-butyrolactones. A variety of 7-(alkoxycarbonyl)-benzofarans and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans were prepared by a cyclization/ dehydrogenation strategy. These reactions rely on cyclizations of 2-oxocycloalkane-1-carboxylate/derived 1,3-dicarbonyl dianions ("free dianions") or 1,3-bis-silyl enol ethers ("masked dianions") with various 1,2-dielectrophiles.