Thallium reagents alkenes

The mechanism of oxidation probably involves in most cases the initial formation of a glycol (15-35) or cyclic ester,and then further oxidation as in 19-7. In line with the electrophilic attack on the alkene, triple-bonds are more resistant to oxidation than double bonds. Terminal triple-bond compounds can be cleaved to carboxylic acids (RC=CHRCOOH) with thallium(III) nitrate or with [bis(trifluoroacetoxy)iodo]pentafluorobenzene, that is, C6F5l(OCOCF3)2, among other reagents. 

A suspension of thallium (III) nitrate in hexane reacts with epoxides to give the corresponding -hydroxy nitrate esters in good yield. The same reagent in acetonitrile has been used to synthesize a-nitratoketones from substituted acetophenones, 1,2-dinitrate esters from alkenes, and 1,3-dinitrates from ring-opening nitration of cyclopropanes. ... 

A suspension of thallium (III) nitrate in pentane at room temperature can react with alkenes to give vtc-dinitrate esters. Cyclohexene reacts with this reagent to give 1,2-cyclohexanediol dinitrate (85 %) (as a mixture of isomers) and 15 % cyclopentanecarboxaldehyde (hydride shift in the dethallation step). Some alkenes react extremely slowly with this reagent e.g. isomeric 5-decenes. 

Similar oxidative rearrangements to produce carbonyl compounds have been carried out with thallium(III) nitrate557 or peroxytrifluoroacetic acid-BF3.558 The Jones reagent (Cr03—H2S04) in the presence of a catalytic amount of Hg(II) is also effective.559 Chromyl chloride oxidation, when combined with reductive workup, is a simple, convenient one-step method to convert 2,2-disubstituted 1-alkenes to aldehydes.560,561... 

Since silver salts are expensive, other cheaper reagents have been sought which can bring about the same type of conversion, and the iodine- tassium iodate- tassium acetate combination has been found to provide a useful alternative. Thallium(I) acetate may be used in place of silver acetate in the Woodward procedure, and syn hydroxylation of steroidal alkenes with dialliumflll) acetate in acetic acid has been performed. ... 

The oxidative reanangement of cyclic alkenes and ketones often leads to ring expansion or ring contraction reactions. The reagents generally used for this purpose are hypervalent main group oxidants such as thallium(III), lead(lV), iodine(III) and selenium(IV), aldiough palladium(II) has been used as well. 

Nitrosolysis of camphor ethyl acetal with ethanolic ethyl nitrite in sulphur dioxide yields the orthoester oxime (205) which is rapidly dehydrated by excess acetal to the orthoester nitrile which then reacts with sulphur dioxide to form the ester nitrile and diethyl sulphite.Further papers in this section include the full paper on ozonolysis of silyl ethers (Vol. 5, p. 33), another synthesis of camphor-enol trimethylsilyl ether (cf. Vol. 6, p. 41)/°° the conversion of camphor oxime with Grignard reagents into the corresponding imine with no aziridine formation/° the preparation of (206) by treating bornylene with trichloroacetyl isocyanate/ the oxidation of thiocam-phor to the 5-oxide and alkylation in the presence of thallium(i) ethoxide to a/S-unsaturated sulphoxides/ and the free-radical C-3 alkylation of camphor with alkenes. " ... 

Mercuric salts induce oxidative rearrangement of cyclic alkenes and give cycloalkane carboxaldehydes. Cyclohexene, for example, gave cyclopentane carboxaldehyde (404) in 53% yield. Acyclic alkenes such as 2-butene can also be oxidized with mercuric sulfate and sulfuric acid, giving 2-butanone in this case.566 Thallium nitrate [T1(N03)3] is an important reagent for the oxidative rearrangement of cyclic alkenes.567 The reaction is not restricted to carbocyclic compounds, but can also be applied to heterocyclic compounds as shown by the oxidation of 3,4-dihydro-277-pyran (405) to the dimethyl acetal (406) in 65% yield.568... 

The value of these reagents results from their specificity and the mildness of the reaction conditions. The reaction proceeds through the formation of an iodonium ion which, in the presence of carboxylate and silver ions, forms the resonance-stabilized cation 93 (5.93). Attack on the cation by the carboxylate anion in an Sn2 process gives the trans-diacyl compound. In the presence of water, however, a hydroxy acetal is formed this breaks down to gives the c/s-monoacylated diol. Note that with conformationally rigid molecules, or indeed with any alkene in which there is a preference for initial attack on one of the two faces of the double bond, the cis-diol obtained by the Woodward-Prdvost method may not have the same configuration as that obtained with osmium tetroxide. Related procedures, that avoid the use of expensive silver salts, have been reported with, for example, iodine and thallium(I) acetate or bismuth(III) acetate. 

---