Decarbonylation of Tetrahydrofuran-2-carboxylic Acids and Tetrahydropyrane-2-carboxylic Acids in Concentrated Sulfuric acid: Formation of Oxonium Ions

Article abstract of DOI:10.1021/ja00373a025

Tetrahydrofuran-2-carboxylic acids 1, 3, and 5 readily decarbonylate in 96percent sulfuric acid, generating stable oxonium ions 2, 4, and 6, respectively.Analogously, tetrahydropyran-2-carboxylic acids 7, 9, 12, and 14a produce oxonium ions 8, 10, 13, and 15, respectively.These oxonium ions are quite stable, with the exception of 10, which partially isomerizes to 11, and 13, which rearranges to ions 17 and 21.Details in the transformation of oxonium ion 15 into lactone 23 by way of open chain acid 22a were elucidated.