6.5- Cyclic thiocarbamates, preparation

Thioxotetrahydro-l,3-0,iV-lieterocycles are commonly named cyclic thiocarbamates or thionocarbamates. The structural association of five- and six-membered thionocarbamates with diverse carbohydrate scaffolds has shown a promising potential in modern organic synthesis and in the preparation of biomolecules mimics. The principal pathways for their synthesis, the recent and most important developments of their chemical transformations as well as some examples of their biological activities will be considered in the following discussion. 

Abstract The high synthetic versatiUty exhibited by the isothiocyanato motif has allowed its use as a building block in the preparation of a plethora of derivatives. When present in carbohydrates, the strong electrophilicity shown by isothiocyanates, together with the possibility of undergoing cycloaddition reactions has made it possible to access a broad spectrum of heterocyclic compounds, of either synthetic or pharmaceutical interest. Among them, noteworthy are 1,3-oxazolidine- and l,3-oxazinane-2-thiones (cyclic thiocarbamates), 2-amino-2-oxazolines (cyclic isoureas), 2-amino-2-thiazolines (cyclic isothioureas), nucleosides, and spironucleosides. 

The same behavior [38] was found for 6,6 -dideoxy-6,-6 -diisothiocyanato-Q ,a -trehalose 5 (Scheme 2), prepared by isothiocyanation of 4. Reactivity of fully-O-protected 6-deoxy-6-isothiocyanato derivatives with ammonia in several solvents to provide either thioureas or cyclic thiocarbamates has also been reported [39]. 

The mono-thiocarbamate complexes [Ni(OSCNR2)2] [R = Me, Et, Pr", Pr , or Bu", R2 = ( 112)4 or (CH2)j] have been prepared. The isopropyl complex is dimeric in the vapour phase and low-polymeric or cyclic oligomeric structures are proposed for the others. Bis-pyridine and bis-pyrrolidine adducts have been isolated. - ... 

Oxathians the formation of cyclic trithio-orthocarbonates (193) by the thermolysis of bis-(dithiocarbonates) the preparation of l,3-oxathiol-2-ones and of 2-substituted 1,3-oxathioles by treatment of moKlibromo-ketones with potassium ethyl xanthate a novel synthesis of 2/f-l,3-benzoxathiol-2-ones (194) by the HI- or pyridine-hydrochloride-induced cyclization of thiocarbamates and the base-catalysed cyclization and Smiles rearrangement of 3-(2,4,6-trinitrophenyl-thio)propanoI to give the benzoxathiepin (195). ... 

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