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

Under the conditions of ruthenium(0)-catalyzed
hydrohydroxyalkylation,
vicinal diols 1a–1l and methyl acrylate 2a are converted to the corresponding lactones 3a–3l in good to excellent yield. The reactions
of methyl acrylate 2a with hydrobenzoin 1f, benzoin didehydro-1f, and benzil tetradehydro-1f form the same lactone 3f product, demonstrating that this process may be deployed
in a redox level-independent manner. A variety of substituted acrylic
esters 2a–2h participate in spirolactone
formation, as illustrated in the conversion of N-benzyl-3-hydroxyoxindole 1o to cycloadducts 4a–4h.
Hydrohydroxyalkylation of hydroxyl-substituted methacrylate 2i with diols 1b, 1f, 1j, and 1l forms α-exo-methylene-γ-butyrolactones 5b, 5f, 5j, and 5l 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 para-substituted 1-phenyl-1,2-propanediols 1g, 1m, and 1n and density functional
theory calculations.