Acid-Mediated Synthesis of Benzofurans from Arylhydroxylamines

Significance

Reported is the methanesulfonic acid mediated synthesis of benzofuran derivatives by aza-Cope rearrangement of hydroxylamine ethers generated from ketones and aromatic ­hydroxylamines. The reaction is potentially quite general in nature, as it proceeds predictably for the examples shown. In the case of 3,3,5,5-tetra­methylhexanone, the reaction is low-yielding (30%) indicating the significance of steric effects, which is also demonstrated by the low yield (41%) of the 2-methylhexanone example. As an added bonus, the use of ketal A as starting material leads to a non-symmetrical dibenzofuran product. This last example merits further investigation.