Carbonyl groups, thiation

Conventional conversion of amide, lactam, imide, and urea carbonyl groups into enaminones, enamino esters, or enamino nitriles requires prior activation of the carbonyl groups either by alkylation to imino ethers, followed by reaction with activated methylene groups, or by thiation, e.g. with P2S5, to thiocarbonyl groups followed by alkylation (and possibly also oxidation), and, again, subsequent reac-... 

The carbonyl group at the 2-position in (236) can be aminated directly using methylamine but the reactivity at this position can be easily enhanced by thiation (p. 617), phosphorylation (p. 618) or conversion to the imidoyl chloride. Similar activation of a 5-oxo group by thiation has been reported (77JHC985). 

The Willgerodt Reaction allows the synthesis of amides from aryl ketones under the influence of a secondary amine and a thiating agent. The mechanism involves the formation of an enamine which undergoes thiation, and the carbonyl group migrates to the end of the chain via a cascade of thio-substituted iminium-aziridinium rearrangements. 

The reactions between Lawesson s reagent and the isomeric aminoketones (299) and (300)(Rp=per luoro C -C alkyl, R =alkyl or Ph) result in thiation of the carbonyl group, as well as formation of isomeric 1,3,2-thiazaphosphorine 2-sulphides having the structures (301) and (302) together with,in some cases, smaller amounts of the 1,3,2-oxazaphosphorine 2-sulphides (303). 

Thiations of phosphoryl groups have occasionally be carried out with 2,4-bis(4-methoxyphenyl)-l,3,2,4-dithiadiphosphetane 2,4-disulphide (55). This, known as Lawesson s reagent, is a powerful reagent, particularly for the thiation of carbonyl groups, and it has been extensively investigated in this respect (the preparation and properties of... 

The reaction of tetrahydrobenzodiazepine-2,5-dione with the reagent formed from phosphorus pentasulfide and butyllithium resulted in thiation of the 2-carbonyl group only <87S162>. 

The thiation procedure described here is an example of a general synthetic method for the conversion of carbonyl to thiocarbonyl groups. Similar transformations have been carried out with ketones, carboxamides,esters,thioesters, 1 actones, " thiol actones, - imides, enaminones, and protected peptides. ... 

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