ChemInform Abstract: Stabilisation of the Thromboxane Ring System by Electron-Withdrawing Substituents. Mechanism and Reactivity in the Hydrolysis of Alkyl and Aryl Oxetane Acetals.
Abstract
Interested in stabilising the oxetane acetal ring system in thromboxane, kinetics of acid-catalysed hydrolysis are measured as a function of pH for eleven oxetane acetals such as (III), (V), and (VII).
ChemInform Abstract
Interested in stabilising the oxetane acetal ring system in thromboxane, kinetics of acid-catalysed hydrolysis are measured as a function of pH for eleven oxetane acetals such as (III), (V), and (VII). The introduction of fluorine atoms into the 2-alkoxy group as in (III) and (VII) results in a 103-104-fold kinetic stabilisation, and the system is also stabilised by 2-aryl substituents as in (III) and (V). The pH-rate profiles for the two most reactive compounds (VII) and (IIIb) (X: -Cl) show that at low pH the reaction involves rapid conversion into the intermediate hemiacetal, followed by its rate-determining break-down into HO-CH2-CMe2-CO-H(Ar). For these compounds, however, at pH greater 6, and for all other oxetane acetals studied, the ring-opening step is rate determining.
