Mechanism of the pinacol–pinacolone rearrangement of 2,3-di-(3-pyridyl)-2,3-butanediol in sulfuric acid

The reaction of 2,3-di-(3-pyridyl)-2,3-butanediol (1) in H2SO4 was studied. It was found that the meso and racemic forms give mono- and bis-SO3 addition products, which rearrange to a ketone (Metopirone®) and two other major by-products. The formation of SO3 addition products and a marked increase in reaction rates with greater amount of SO3 suggest an alternate mechanism involving sulfonyloxy leaving groups.