Flavonoid epoxides. Part 17. Stereospecific synthesis and acid-catalysed rearrangement of aurone epoxides
The configurations of 6-methoxyaurone epoxides were determined by direct epoxidation of the parent aurones (1) and (2) by m-chloroperbenzoic acid. trans-6-Methoxyaurone epoxide (3) was also synthesised indirectly through the intermediacy of the reduced ketone derivatives (4) and (5) of aurone (1) and aurone epoxide (3). m-Chloroperbenzoic acid was found to be complementary to alkaline hydrogen peroxide as an epoxidation agent for various aurones. Coumarins (10) were obtained on acid-catalysed rearrangement of aurone epoxides (8). The chlorohydrin derivative (11) of aurone epoxide (3), on treatment with alkali, gave the corresponding flavonol (12). Reduced aurone epoxide (5) gave aurone (1) on treatment with hydrochloric acid.