Indium-promoted butenolide synthesis through consecutive C–C and C–O bond formations in aqueous tetrahydrofuran enabled by radicals

An indium-promoted lactonization of (indol-3-yl)-2-oxoacetaldehydes, which allows the synthesis of substituted γ-methylenebutenolides in an aqueous environment, has been accomplished. This process is in clear contrast with the established metal-mediated reactivity of unsaturated organic halides and carbonyls. The use of an aqueous medium and the facile purification profile make our protocol a convenient and sustainable synthetic strategy. A plausible reaction pathway has been proposed with the help of density functional theory calculations.