Lactonization of o-Arylethenylbenzoic acids: Formation of 3,4-dihydro- 1 H-2-benzopyran-1-ones and isobenzofuran- 1(3H)-ones

Abstract

The formation of six 3,4-dihydro-1H-2-benzopyran-1-ones (2a-f) and one isobenzofuran-1(3H)-one (3a) from o-arylethenylbenzoic acids (1) in neutral or acid solution is described. The benzoic acids having a neutral or electron-releasing group on the double bond give δ-lactones (2), whereas compounds with a strong electron-withdrawing group give the γ-lactones (3). The mechanism is discussed in terms of electronic effects. The rate of cyclization of the (Z)-compound is found to be faster than that of the (E)-compound.