Nucleophilic substitution thiocarbonylation

Aryl thionoesters (54a) may be prepared by nucleophilic substitution reactions of aryl thiocarbonyl halides with alcohols or phenols for instance, thiobenzoyl chloride (58) condenses with phenol to yield the diaryl ester (54a) (Scheme 30). 

The reliability and usefulness of a new empirical nucleofugality index, which is defined as the group electrophilicity of the leaving group embedded in the substrate that undergoes the nucleophilic attack, were tested against experimental kinetic data recorded for aminolysis reactions of variously substituted phenoxy- and thiophenoxy-carbonyl and the corresponding thiocarbonyl derivatives.50... 

A new class of nucleophiles have been introduced for sulfur addition. Degl Innocenti and his group [145, 146] have shown that allyl or benzylsi-lanes, in the presence of tetra-n-butylammonium fluoride, reacted in a thiophilic fashion and led to allyl sulfides or dithioacetals. It is remarkable that this selective reaction is general for a large variety of thiocarbonyl compounds thioketones [145], dithioesters [146], and even with the normally sluggish trithiocarbonates [145]. With substituted allyl silanes retention of configuration of the allyl chain is observed. It is noteworthy that the possible [2,3] sigmatropic shift of the intermediate anionic species was not observed. 

The need for a variety of organofluorine molecules has encountered difficulties with oxygenated substitutes such as carboxylic esters due to their poor nucleophilicity towards electrophilic fluorinating reagents. This has led several groups to explore the conversion of the thiocarbonyl group into the CF2 moiety. It was successful with thioamides [174], dithioesters [175-177] and thionoesters [178, 179], providing new routes to difluoro-sulfides, amines, ethers and alkenes. 

The coordinated thiocarbonyl group more readily undergoes nucleophilic attack on the carbon atom and electrophilic attack on the sulfur atom than does the carbonyl group. Moreover, thiocarbonyl complexes may participate in reactions in which the thiocarbonyl group itself does not change, for example, substitution reactions involving ligands other than CS. 

Reactions.— The nucleophilic reactivity of the thiocarbonyl sulphur atom in thioureas has been further exemplified in a series of papers reporting on S-alkylation reactions of open-chain " as well as cyclic thioureas using alkyl halides. Ried and his co-workers have reported that (4-quinazolyl)thioureas (315) react smoothly with methylene iodide in the presence of triethylamine to yield the 1,3-thiazetidines (316). The ready formation of (316) was attributed to the special effect of the intramolecular hydrogen bonding in (315), as common thioureas usually did not enter into this reaction in a well-defined and profitable way. 5,5-Diphenyl-2-thio-hydantoin reacted with symmetrical ao>-dibromo-alkanes to yield the cyclization products (317). The action of excess of methyl iodide on N -substituted N-(o-aminophenyl)thioureas afforded the benzimidazoles (318), alternatively obtainable by treatment of the same thioureas with mercuric chloride." " In a similar manner, l-amino-6,7-dimethoxy-3,4-di-hydroisoquinolines were formed by the action of mercuric chloride on the thioureas (319)" or their S-methyl derivatives (320). " A recent paper by Klayman and his co-workers deals with the reactivity of S-methiodide derivatives of thioureas that are activated by electron-withdrawing groups towards hydroxylic compounds. "... 

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