Photo-oxidative Cyclization of Morusin

When a solution of morusin (I) in CHCl_3 or benzene was exposed to bright sunshine, or irradiated with a high-pressure mercury lamp, morusin hydroperoxide (III) was obtained in a high yield. The reduction of III gave compound A (II) which had been isolated from the root bark of Morus alba L. The reaction mechanism of the photooxidation was discussed based on the several experimental results.