Conversion of xanthates

Oxidation. Bis(p-methoxyphenyl)telluroxide (1) is a mild and selective oxidant for conversion of xanthates, thiocarbamates, thioamides, and nonenolizable thiones into the corresponding oxo derivatives, and also of thiols into disulfides. Typically these reactions afford products in 70-100% yield. 1,2- and 1,4-Hydroquinones are oxidized by 1 to o- and p-quinones, respectively. Phenylhydroxylamine is oxidized to nitrosobenzene (90% yield). Phenols, amines, enamines, alcohols, oximes, dithiolanes, isonitriles, and 2,4-dinitrophenylhydrazones are unreactive. 

Scheme 7 Conversion of xanthate chain-ends into hydroxyl and aldehyde end-groups. Reprinted with permission from Pound, G. McKenzie, J. M. Lange, R. F. M. Klumperman, B. Chem. Commun. 2008, 44, 3193-3195. Copyright 2008 The Royal Society of Chemistry.

FREUDENBERG - SCHdNBERG Xanthate Rearrangement Rearrangement of S-methyl xanthates to S-methyIdithiocarbonatas (conversion of alcohols lo thiols via xanthates, also phenols to thiophenols via thiocarbamates). 

Extension of these processes to provide enantio-enriched products was successfully applied after desymmetrization of the starting materials. An example is shown below (Reaction 76), where silane-mediated xanthate deoxygenation-rearrangement-electrophile trapping afforded the conversion of (+)-94 to (+)-95 in 56% yield. ... 

The standard conversion of alcohols into their xanthate esters through reaction with carbon disulphide and an alkylating agent is improved by the addition of a quaternary ammonium salt [69]. Excellent yields (>90%) are obtained in relatively short reaction times under mild conditions. The formation over relatively short reaction times of O-glycosyl xanthates from partly protected glycosides has been described using a stoichiometric amount of the quaternary ammonium salt [70]. 

Amongst the important chemical conversions of macromolecular substances are the various reactions of cellulose. The three hydroxy groups per CRU can be partially or completely esterified or etherified. The number of hydroxy groups acetylated per CRU are indicated by the names, i.e., cellulose triacetate, cellulose 2-acetate, etc. Another commercially important reaction of cellulose is its conversion to dithiocarboxylic acid derivatives (xanthates). Aqueous solutions of the sodium salt are known as viscose they are spun into baths containing mineral acid, thereby regenerating the cellulose in the form of an insoluble fiber known as viscose rayon. 

Deoxygenation of allyttc alcohols.3 A method for conversion of allylic alcohols to l-alkenes is outlined in equation (I). The first step is an allylic rearrangement of an Oallyl xanthate to 2. The second step is an allyl transfer from sulfur to tin with tri-n-butyltin hydride to give the allylic stannane (3). The last step, destannylation, is a well-known mule to terminal alkcnes.4... 

The conversion of alcohols to xanthate esters, and treatment of the latter with DFIT provides access to 1°- and 2°-alkyl fluorides, probably through intermediates of the type shown in Scheme 38 [108]. 

It has been shown that the xanthate method could be successfully applied in order to graft hardwood high yield bisulfite pulp made of aspen. The optimum grafting condition, which would give almost 100% grafting efficiency (i.e.,100% formation of true graft and no homopolymer) and rather high monomer conversion of 80% are as follows ... 

Since it seemed likely that a xanthate function beta to a carbon radical would eliminate to furnish a double bond, we studied the tin hydride reduction of 1,2-dixanthates.1112 This provided an efficient new synthesis of olefins which was independent of the stereochemistry of the glycol. It was particularly suitable for the conversion of protected ribosides 23 via the dixanthates 24 into the corresponding olefins 25 from which biologically important dideoxynucleosides 26 were readily obtained by hydrogenation and deprotection.13... 

Although it was known in the years following the discovery by Cross and Bevan that a viscose type of solution could be used in the preparation of regenerated cellulose, the conversion of this solution into useful fibers was not possible until the discovery that the solution required aging until ripe. Ripening is the first part of the actual chemical decomposition of cellulose xanthate, which, if allowed to proceed unhampered, would result in gelation of the viscose solution. 

Barton and coworkers developed a very useful procedure for the deoxygenation of alcohols, which involves conversion of the alcohol to the corresponding xanthate derivative followed by reaction with BuaSnH. When applied to the bis(xanthates) derived from v/ c-diols the reaction gives alkenes, as illustrated in equation (17). Once again alkene formation is independent of the stereochemistry of the starting diols. 

Carbon disulfide is an important industrial solvent for the extraction of oils and waxes. In organic chemistry, it is widely used as a solvent for Friedel-Crafts reactions. Carbon disulfide functions as an electrophilic reagent. It is more susceptible than carbon dioxide to nucleophilic attack as the energy required to convert C=S to C-S (188 kJmol 1) is much less than required for the analogous conversion of C=0 to C-0 (305 kJmol 1). Carbon disulfide (1) thus undergoes nucleophilic additions with alcohols and phenols to yield the corresponding xanthates (2) (the xanthate reaction) (Scheme 2)... 

Conversion of the precursor 22 by initial cleavage of the xanthate unit, and subsequent acid-induced cyclization provided a route to the dihydrothiophene 23. Similar cyclization of substrates where the pivaloyl group was replaced with TBDPS or acetyl groups gave considerably lower yields of the corresponding dihydrothiophenes <05TL8053>. 

Tschugaefi reaction. In the Tschugaeff reaction1 for the conversion of alcohols into olefins, the sodium salt of the alcohol is treated with carbon disulfide and then an alkyl halide, usually methyl iodide the resulting xanthate is then pyrolyzed ... 

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