STABILIZATION OF THE THROMBOXANE RING-SYSTEM BY ELECTRON-WITHDRAWING SUBSTITUENTS - MECHANISM AND REACTIVITY IN THE HYDROLYSIS OF ALKYL AND ARYL OXETANE ACETALS

Rates of acid-catalysed hydrolysis are reported as a function of pH for eleven oxetane acetals (6) in 20% dioxane-water. The introduction of fluorine atoms into the 2-alkoxy group results in a 103-104-fold kinetic stabilisation, and the system is also stabilised by 2-aryl substituents. The pH-rate profiles for the two most reactive compounds (3b) and (12b) show that at low pH the reaction involves rapid conversion into the intermediate hemiacetal, followed by its rate-determining decomposition. For these compounds at pH > 6, and for all other oxetane acetals studied, the ring-opening step is rate determining. No general acid catalysis is apparent.