Novel Spiroacetal Synthesis via Hydroboration of Alkynediols

Alkynediols were transformed to the corresponding spiroacetals by the sequence of hydroboration with disiamylborane, oxidation of the resulting alkenylboron intermediate with alkaline hydrogen peroxide, and catalytic treatment with p-TsOH. By this transformation, 6-(2-hydroxymethyl)phenyl-3-methyl-5-hexyn-1-ol was converted to spiro[3,4-dihydro-1H-2-benzopyran-3,2′-[4′]methyl[3′,4′,5′,6′]tetrahydro-2′H-pyran] as a single diastereomer.