Thiols reaction with strong bases

In this section, we discuss the acidity of thiols and their reaction with strong bases, such as sodium hydroxide, and with molecular oxygen. 

Vinyl chloride reacts with sulfides, thiols, alcohols, and oximes in basic media. Reaction with hydrated sodium sulfide [1313-82-2] in a mixture of dimethyl sulfoxide [67-68-5] (DMSO) and potassium hydroxide [1310-58-3], KOH, yields divinyl sulfide [627-51-0] and sulfur-containing heterocycles (27). Various vinyl sulfides can be obtained by reacting vinyl chloride with thiols in the presence of base (28). Vinyl ethers are produced in similar fashion, from the reaction of vinyl chloride with alcohols in the presence of a strong base (29,30). A variety of pyrroles and indoles have also been prepared by reacting vinyl chloride with different ketoximes or oximes in a mixture of DMSO and KOH (31). 

The combined information gathered from kinetic studies,184 in situ high-pressure NMR experiments,184,185,195 and the isolation of intermediates related to catalysis, leads to a common mechanism for all the hydrogenolysis reactions of (102)-(104) and other thiophenes catalyzed by triphos- or SULPHOS-rhodium complexes in conjuction with strong Bronsted bases. This mechanism (Scheme 41) involves the usual steps of C—S insertion, hydrogenation of the C—S inserted thiophene to the corresponding thiolate, and base-assisted reductive elimination of the thiol to complete the cycle.184 185 195-198... 

Pyrimidine thioethers may also be synthesized via direct Pd-catalyzed C—S bond formation between halopyrimidines and thiolate anions. For very unreactive thiol nucleophiles such as 2-thiopyrimidine, both a strong base and a palladium catalyst are essential. Without a palladium catalyst or replacing f-BuONa with K2C03, the reaction failed to furnish the desired pyrimidine thioether [49]. 

As a relatively unusual reaction, it has been reported that the ring opening reaction of carbolinium salts with a variety of thiols was facilitated by the use of PS-TBD as a strong base [62] (Scheme 6.14). 

Ketones can be reduced to secondary alcohols by H and a catalyst or a complex metal hydride or by hydrogen transfer reagents. Deoxygenation with a strong base at 150°C (302°F) can form olefin. Ketones react with thiols to form thioacetals. Reaction with anhydrous hydrazine may be explosive. 

The substitution reactions discussed in this review will be restricted primarily to the thiolate anion, RS acting as a nucleophile. This may be present initially when a metal thiolate, such as silver(i) or lead(ii), is employed, or may be generated in solution in the presence of a base such as sodium hydroxide or trimethylamine. The acidity of the thiol is important if the RS anion acts as a nucleophile in a neutral thiol solution. Thiolate nucleophiles can be obtained in non-aqueous solution by treatment of thiol esters, such as CH3COSR, with strong non-nucleophilic basest or by hydrolysis of thiourea derivatives ... 

Thiols have been employed as nucleophiles in palladium-catalysed coupling reactions (Scheme 2.181). An aryl thioether could be formed from an aryl triflate using a strong base, a bidentate ligand and a nonpolar solvent to suppress competitive triflate decomposition. An intramolecular thiol coupling with an iodoindole was a key step in a synthesis of chuangxinmycin (Scheme 2.182). ... 

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