carbonyl group and an ethoxycarbonyl group), aryloxycarbonyl groups (each preferably having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, and particularly preferably 7 to 10 carbon atoms; such as a phenyloxycarbonyl group), acyloxy groups (each preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, and particularly preferably 2 to 10 carbon atoms; such as an ac