Oxydation des alcènes par l'ion thallique. I. Stéréochimie et mécanisme de l'oxydation des cyclohexènes

Abstract

R e~u le 15 mars 1971 L'Ctude de la stBrBochimie des diols form& dans I'oxydation du tert-butyl-3 cyclohexene par le sulfate thallique a permis de mettre en Bvidence la participation du groupe hydroxyle en a lors de la rupture de la liaison C-TI de I'intermBdiaire organothalleux. En effet, seuls les diols trans ont Bt B obtenus ce qui exclut la substitution SN2 par I'eau. I1 est suggQB que l'oxydation thallique en milieu aqueux peut constituer une synthese en une seule Btape de diols trans dans le cas des systkmes rigides oh l'organothalleux intermdiaire a une configuration diaxiale. La formation d'un seul diol diaxial lors de l'oxydation du tert-butyl-4 cyclohexene tend ti confirmer cette hypothbe.The stereochemistry of the diols obtained by oxidation of 3-t-butylcyclohexene by thallic sulfate indicates that the a hydroxyl group participates in the breaking of the C-T1 bond of the intermediate organothallous compound. The fact that only the trans diols are obtained indicates that an SN2 substitution of the thallium can be excluded. We suggest that the thallic oxidation in aqueous media of olefin of rigid conformation is an excellent one-step method of preparing trans diols. The formation of the trans diaxial diol upon oxidation of 4-t-butylcyclohexene tends to confirm that hypothesis.

On the Mechanism and Substituent Effects of the Tl(III) Oxidation of Phenylethylenes in Methanol

“…The rate constants which were measured under A consideration of all the results reported in various experimental conditions are indicated in the literature indicates that step [3] consists in Table 1. a competition between two possible reaction The present kinetic results are thus in accord paths. These are indicated in Scheme 1, which with those reported by Henry (1) for thallic unifies the proposals which have been considered oxidations in water and by Ouellette et al (9) for (2,5,6,9) for various specific experimental conthe oxidation of styrenes by thallic acetate in ditions and is capable of explaining the depenCan. J. Chem.…”

“…Such a participation of OR should be favored over an S,2 substitution of T1 by a solvent molecule, as demonstrated in the case of rigid cyclohexenes (5).…”

“…The oxidation of a great number of olefins by thallic salts has been the object of intensive recent studies (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), from the point of view of both preparative organic chemistry and of the interesting mechanistic implications. From Henry's fundamental studies, including product distributions and kinetic considerations, a basic mechanistic proposal has developed for the oxidation of a variety of simple olefins by Tl(II1) in aqueous acid solutions (1,2).…”

Etude de l'oxydation des éthylènes RCH=CH2 et R1(R2)C=CH2 par le Tl(NO3)3 dans le méthanol

“…La rupture du lien C-TI et la migration de l'alkyle seraient alors concerties. Ceci est en accord avec 1'Ctude sttreochimique de l'oxydation de cyclohexenes rigides qui conclut que la dicomposition de l'organothallique intermediaire n'est pas initite par la rupture de la liaison C-TI (10).…”

Thallic Ion Oxidation of Styrene: Kinetics of Decomposition of the Oxythallation Adduct C6H5—CH(OCH3)—CH2Tl(OAc)2

“…However, Henry's first kinetic measurements (13) suggested interesting mechanistic implica-[2bl TI+ + CH2-CHR + H + tions and thus prompted several recent kinetic I I studies (14)(15)(16)(17)(18)(19). The kinetics and product distri- OH OH bution for the oxidation of manysimple olefins by TI (111) in aqueous acid solutions have been Reaction 1 represents the formation of an orinterpreted by Henry in terms of the following gano-thallic intermediate (1); it is followed by mechanism : the decomposition of 1 into the final products reactions (2a and 2b).…”