Ruthenium-Catalyzed Hydrohydroxyalkylation of Acrylates with Diols and α‑Hydroxycarbonyl Compounds To Form Spiro- and α‑Methylene-γ-butyrolactones

Abstract

Under the conditions of ruthenium(0)-catalyzed hydrohydroxyalkylation, vicinal diols <b>1a</b>–<b>1l</b> and methyl acrylate <b>2a</b> are converted to the corresponding lactones <b>3a</b>–<b>3l</b> in good to excellent yield. The reactions of methyl acrylate <b>2a</b> with hydrobenzoin <b>1f</b>, benzoin <i>didehydro</i>-<b>1f</b>, and benzil <i>tetradehydro</i>-<b>1f</b> form the same lactone <b>3f</b> product, demonstrating that this process may be deployed in a redox level-independent manner. A variety of substituted acrylic esters <b>2a</b>–<b>2h</b> participate in spirolactone formation, as illustrated in the conversion of <i>N</i>-benzyl-3-hydroxyoxindole <b>1o</b> to cycloadducts <b>4a</b>–<b>4h</b>. Hydrohydroxyalkylation of hydroxyl-substituted methacrylate <b>2i</b> with diols <b>1b</b>, <b>1f</b>, <b>1j</b>, and <b>1l</b> forms α-<i>exo</i>-methylene-γ-butyrolactones <b>5b</b>, <b>5f</b>, <b>5j</b>, and <b>5l</b> in moderate to good yield. A catalytic cycle involving 1,2-dicarbonyl–acrylate oxidative coupling to form oxaruthenacyclic intermediates is postulated. A catalytically competent mononuclear ruthenium­(II) complex was characterized by single-crystal X-ray diffraction. The influence of electronic effects on regioselectivity in reactions of nonsymmetric diols was probed using <i>para</i>-substituted 1-phenyl-1,2-propanediols <b>1g</b>, <b>1m</b>, and <b>1n</b> and density functional theory calculations