Photochemical and mass spectrometric transformation of gibberellenic acid to 9-epiallogibberic acid

Abstract

Gibberellenic acid (2) reacted thermally in a modified immersion photochemical reactor, to give an intermediate triene (3). This triene then isomerized photochemically, via suprafacial [1,3]-hydrogen migration, to 9-epiallogibberic acid (5). On the other hand, comparison of the positive mass spectra of gibberellenic acid (2), allogibberic acid (4), and 9-epiallogibberic acid (5) showed that gibberellenic acid underwent electron impact fragmentation to the triene 3 cation. This cation then rearranged through suprafacial [1,3]-hydrogen migration to the 9-epiallogibberic acid (5) cation.