Bis(acetylacetonato)dioxomolybdenum(VI) catalysed rearrangement of methylbutynol in the presence of ultrasound

The molybdenum (VI) catalysed rearrangement of methylbutynol was carried out under the influence of ultrasound (20 kHz). Surprisingly, 2-methylpropene (isobutene) was found as the main product. The formation of isobutene can be explained by rearrangement to prenal, oxidation to 3,3-dimethylacrylic acid and then decarboxylation. 3,3-dimethylacrylic acid was decarboxylated in the presence of ultrasound and a catalyst; without a catalyst or without ultrasound (at 50°C) it remained unchanged.