Xanthates from alcohols

For a method of preparing xanthates from alcohols in one laboratory step, see Lee Chan Wong Wong Synth. Commun. 1989,19, 547. 

Aryl Xanthates. It is 165 years since Zeise (8) reported the formation of xanthates from alcohol and CS2 on reaction with base. Yet only three papers, a 1948 Itahan patent (9), a 1970 report by Lee (10), and a recent (1971) report by Reichle (11), relate to the synthesis of aryl xanthates. We established (12) that the Italian patent is incorrect. 

Without additional reagents Alkali xanthates from alcohols... 

Without additional reagents Alkali xanthates from alcohols Prepn. of alkali alkoxides with alkali hydroxides... 

Various xanthates can be readily prepared ia the laboratory from alcohols (up to C ), potassium hydroxide, and carbon disulfide (68). 

Olefin formation (preferentially less substituted) from alcohols via xanthate pyrolysis. 

The required xanthates 1 can be prepared from alcohols 5 by reaction with carbon disulfide in the presence of sodium hydroxide and subsequent alkylation of the intermediate sodium xanthate 6. Often methyl iodide is used as the alkylating agent ... 

The thermolysis of xanthates derived from primary alcohols yields one olefin only. With xanthates from secondary alcohols (acyclic or alicyclic) regioisomeric products as well as fi/Z-isomers may be obtained see below. While acyclic substrates may give rise to a mixture of olefins, the formation of products from alicyclic substrates often is determined by the stereochemical requirements the /3-hydrogen and the xanthate moiety must be syn to each other in order to eliminate via a cyclic transition state. 

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]. 

Another method that provides chlorides from alcohols with retention of configuration involves conversion to a xanthate ester, followed by reaction with sulfuryl chloride. This method is thought to involve collapse of a chlorinated adduct of the xanthate ester. The reaction is useful for secondary alcohols, including stoically hindered structures.8... 

An instructive example on how stereochemical features influence the stereochemical outcome of the elimination is the pyrolysis of xanthates from erythro-and f/treo-1,2-diphenyl-1-propanol. The erythro-alcohol 8 is converted into E-methylstilbene 9 only, and the f/ireo-alcohol 10 is converted into the corresponding Z-isomer 11 only. These results support the assumption of a syn-elimination process through a cyclic transition state ... 

Radical deoxygenation of alcohols is important, and the reduction of xanthates prepared from alcohols, with Bu3SnH in the presence of AIBN is called the Barton-McCombie reaction (eq. 2.13) [37-51]. The driving force for the reaction is the formation of a strong C=0 bond from the C=S bond, approximately 10 kcal/mol stronger. This reaction can be used for various types of substrates such as nucleosides and sugars. Though methyl xanthates, prepared from alcohols with carbon disulfide and methyl iodide under basic conditions are very frequently used, other thiocarbonates, as shown in eq. 2.14, can also be employed. 

Other C=S-containing esters derived from alcohols can also be defunctionalized in a similar fashion. Imidazolylthiocarbonic esters, which in contrast to xanthates can be synthesized under neutral conditions, are one example. This is important for the reduction of base-sensitive alcohols. Figure 1.41 shows a reaction of this type. If the corresponding xanthate was pre-... 

The stereochemistry of the reaction depended on the substrate in some favourable cases a single stereoisomer was formed, whereas in others mixtures of a,/ -isomers were obtained. An increase in yield was noted when the phenyl group of the thioglycoside was replaced by the 4-chlorophenyl group. Another useful fluorination involved xanthate esters, ROCSSMe, readily obtained from alcohols these upon reaction with 4-(difluoroiodo)toluene were converted into alkyl fluorides in 48-75% yield [54],... 

In a related study, Lusinchi [11] reported the synthesis of a new soluble polymer containing a p-alkoxybenzyl alcohol linker, analogous to Wang resin. The polymer was utilized in intermolecular radical addition reactions. The polymer was synthesized by subjecting xanthate 65, formed in three steps from alcohol 63, to styrene polymerization in the presence of lauroyl peroxide... 

The replacement of an amino group by a mercapto group on an aromatic nucleus is effected by treating the diazotized amine with potassium ethyl xanthate and hydrolyzing the resulting aryl ethyl xanthate (Leuckart). Yields of 40-80% are reported for thiophenols containing methyl, halo, and methoxyl groups. Potassium ethyl xanthate is readily prepared from alcoholic potassium hydroxide and carbon disulfide. ... 

The organic portion, R, in the xanthate is generally obtained from alcohols ranging from ethyl to amyl (C2H5OH to C Hj OH). 

Chugaev reaction. Formation of olefins from alcohols without rearrangement through pyrolysis of the corresponding xanthates via cis elimination. 

Friedel-Crafts acylation 44, 956 halides from alcohols via xanthates 44,430... 

Chlorides from alcohols via xanthates Retention of configuration... 

Aryl xanthates mainly comprise phenmethyl and cinnamyl xanthates. Benzyl alcohol xanthate can be prepared from benzyl alcohol ... 

Pyrolysis of the xanthate or acetate is the normal method for olefin formation from alcohols, which avoids carbonium ion intermediates. In the case of... 

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