Vinyl ether hydrolysis. XIV. 2-Methoxy-2,3-dihydropyran: concurrent reaction of vinyl ether and acetal functional groups

Abstract

. Can. J. Chem. 58,2199Chem. 58, (1980. The hydrolysis of 2-methoxy-2,3-dihydropyran shows a normal isotope effect (kH/kD > 1) under catalysis by the hydrogen ion and gives an accurately linear dependence of reaction rate upon undissociated acid concentration in cyanoacetic acid and formic acid buffer solutions. This substrate, therefore, unlike its higher homolog, 9-methoxyoxacyclonon-2-ene, provides no evidence in support of an anything but a normal mechanism for vinyl ether hydrolysis. Analysis of the hydrogen isotope effect suggests that a 1 minor amount (8%) of this hydrolysis occurs via reaction of the acetal functional group. R. A. BURT, Y. CHIANG et A. J. KRESGE. Can. J. Chem. 58,2199Chem. 58, (1980. L'hydrolyse du methoxy-2 dihydro-2,3 pyranne catalysee parl'ion hydrogkne, montre un effet isotopique normal (kH/kD> 1) et sa vitesse de reaction depend d'une f a~o n precise et lineaire de la concentration en acide non dissocie dans des solutions tampons d'acides cyanoacktique et formique. Dans le cas de ce substrat, contrairement a son homologue superieur, le methoxy-9 oxacyclononbne-2, toutes les donnkes indiquent que la reaction se produit par un mtcanisme d'hydrolyse normal pour les ethers vinyliques. L'analyse de I'effet isotopique de I'hydrogkne suggkre qu'une partie infime (8%) de cette hydrolyse se produit par I'intermediaire de la reaction du groupe fonctionnel acttal.[Traduit par le journal]In order to gain information which might be of use in understanding the unusual hydrolytic behavior of 9-methoxyoxacyclonon-2-ene,3 1 (I), we have investigated the acid-catalyzed hydrolysis of the related substance, 2-methoxv-2.3-dihvdropyran, 2. The hydrolysis of a homoiog of 2, i-ethn oxy-2,3-dihydropyran, had been examined before (2), but that study was limited to HCl solutions. ether functional group. In carboxylic acid buffer solutions, however, its behavior deviates from that of all other vinyl ethers examined so far, and we were particularly interested, therefore, in studying a similarly substituted vinyl ether in these media. ExperimentalMaterials 2-Methoxy-2,3-dihydropyran was purchased from the Aldrich Chemical Company. Its proton nmr spectrum was consistent with its structure and showed no sign of impurities, but kinetic data for the hydrolysis of the commercial material nevertheless sometimes produced curved first-order plots. Samples freshly purified by gas chromatography, on the other hand, were well behaved, and kinetic measurements were therefore carried out on material purified in this way.Acids were best available commercial grades and were usedIn dilute aqueous HC1, 1 behaves normally in a without further treatment. Solutions were made using either manner characteristic of the hydrolysis of its vinyl deionized H 2 0 purified further by distillation from alkaline permanganate or D 2 0 as received (Merck); buffer solutions were prepared by adding requisite amounts of aqueous sodium hy-'Part XIII: Y. Chiang, W. K. Chwang, A. J. Kresge, and S. droxide to acid solutions. Szilagyi. Can. J. Chem. ...

Mechanistic Investigations of Unsaturated Glucuronyl Hydrolase from Clostridium perfringens

“…Beyond suggesting that proton transfer events are involved in both of the kinetically important steps, few conclusions can be drawn from this. Notably, solvent KIEs for the few cases of hydrolysis of vinyl ether acetals that have been determined to proceed by initial hydrolysis of the acetal moiety are around 0.37 to 0.55 (26,31,32), but values for hydration of vinyl ethers range from 1.56 to 7.1 (26,(31)(32)(33)(34). The values determined for UGL clearly fall within the latter range rather than the former, and so are more consistent with a hydration mechanism than a more traditional glycoside hydrolase mechanism, which would act at the acetal first.…”

Mechanism of Hydrolysis of Isopropenyl Glucopyranosides. Spectroscopic Evidence Concerning the Greater Reactivity of the α Anomer

“…Propenyl acetals, such as 3 , hydrolyze with exclusive cleavage of the acetal C−O bond , The rate of acetal hydrolysis in 4 may be attenuated by intramolecular collapse of the oxocarbenium ion with the enol leaving group. …”