Photo-irradiation of friedelin (1) in diethylether gave a keto ether (2), a hydroxy ether (3), and an alcohol (4). A hydroxy ketone (5) was formed by the photo-irradiation reaction of 1 in diethylether containing acetone. In the latter case, labeled experiments showed that the photo-produced ketene (12) reacted with 1-hydroxy-1-methylethyl radical derived from acetone to give 5. The formation of