Thiolactones anhydrides

These methods parallel the synthesis just described for the five-membered rings. As indicated in structures (42)—(49), standard reactions of aliphatic chemistry can be extended to the preparation of piperidines, tetrahydropyrans and pentamethylene sulfides (44 Z = N, O, S) glutarimides, glutaric anhydrides and glutaric thioanhydrides (46 Z = N, O, S) and 8-lactams, 8-lactones and 8-thiolactones (49 Z = N, O, S). 

The construction of the maleic anhydride moiety 44 in only five steps starts with the conversion of the amide into an appropriate thioester. Upon treatment with DBU, an aldol-type cyclization occurs to provide the /1-hydroxy thiolactone as a single diastereomer. After removal of the allylic protecting group, dehydration and decarboxylation are carried out simultaneously by simple heating. The thiobutenolide is oxidized to the corresponding thio-... 

Dehydration of a thiol add with phosphoric anhydride at about 100 also gives a thiolactone " ... 

The first (3-thiolactone was prepared according to Scheme A by Knunyants and co-workers. A mixed anhydride of )3-mercaptocarboxylic acid and carbonic-acid ester is obtained by treatment of a salt of the mercapto acid with a chlorocarbonate ester.Cyclization to the 3-thiolactone occurs during the reaction this synthetic method is exemplified by the preparation of 302 from 301. A mixed carboxylic-sulfonic acid anhydride is involved in the formation of the thiolactone ring in 303. ... 

Oxidation of (3-thiolactone 308 with m-chloroperbenzoic acid gives a low yield of the mixed sulfinic-carboxylic acid anhydride 331. ... 

---