Photochemicalreactions of 5-fluorocytosine with primary alcohols led to 5-alkoxycytosines and 6-alkoxycytosines as the main photoproducts. These products are formed via reactive intermediates 6-alkoxy-5-fluoro-5,6-dihydrocytosines, whereas photochemicalreactions of 5-fluorouracil with alcohols led to stable 6-alkoxy-5-fluoro-5,6-dihydrouracils.