The intramolecular acylation of some hex-, hept-, and oct-enoic acids

Abstract

Treatment of any of the seven isomeric hexenoic acids with polyphosphoric acid at 100° yields essentially the same mixture of cyclohex-2-enone, 2-methylcyclopent-2-enone and hexan-4- and 5-olide. Comparable results are obtained with heptenoic and octenoic acids. Intramolecular acylation of these acids in the presence of trifluoroacetic anhydride is shown to be dependent on the structure and stereochemistry of the acids. The formation of cyclohept-2-enone from hept-6-enoic acid is reported. Concentrated sulphuric acid in acetic anhydride is shown to convert hex- and hept-5-enoic acid into phenyl and o-tolyl acetate, respectively. Some improved syntheses of alkenoic acids are reported.