Sulfur-containing heterocyclic ring

In Carmack s mechanism, the most unusual movement of a carbonyl group from methylene carbon to methylene carbon was proposed to go through an intricate pathway via a highly reactive intermediate with a sulfur-containing heterocyclic ring. The sulfenamide serves as the isomerization catalyst ... 

Of the possible four-membered sulfur-containing heterocyclic rings that contain another heteroatom, which is not sulfur, oxygen, or nitrogen, only the thiaphosphetanes, silathietanes, and selenathietanes are discussed in the literature up to 1980. 

This reaction can be carried out internally, by treatment of sulfide ions with 1,4- or 1,5-dihalides, to prepare five- and six-membered sulfur-containing heterocyclic rings. 

Sulfur-containing heterocyclic rings are readily desulfurized by treatment with Raney nickel. Thus the 1,2,4-thiadiazine (146) is fully desulfurized and cleaved to give (147) (67CB2159). Similarly, Raney nickel treatment of (148) gives RO2CNHNHCO2R... 

This reaction can be carried out internally, by treatment of sulfide ions with 1,4-, 1,5-, or 1,6-dihalides, to prepare five-, six-, and seven-membered sulfur-containing heterocyclic rings. Certain larger rings have also been closed in this way. A related variation converts epxoides to thiiranes with thiourea and LiBp4 in... 

A generalized reaction scheme has been developed for the reactions of thiosemicarbazides with a-halocarbonyl compounds. Depending on whether condensation occurs at the N1, N2, or N4 atom, three different sulfur-containing heterocyclic rings may be expected after ring closure 1,3,4-thiadiazines, 2-alkyl(aryl)imino-2,3-dihydrothiazol-3-amines, and 3-alkyl(aryl)-2-hydra-zono-2,3-dihydrothiazoles as well as, with R3 = H, thiazole-2-hydrazines (see p 494). 

Active Raney nickel induces desulfurization of many sulfur-containing heterocycles thiazoles are fairly labile toward this ring cleavage agent. The reaction occurs apparently by two competing mechanisms (481) in the first, favored by alkaline conditions, ring fission occurs before desul-, furization, whereas in the second, favored by the use of neutral catalyst, the initial desulfurization is followed by fission of a C-N bond and formation of carbonyl derivatives by hydrolysis (Scheme 95). 

Sulfur containing heterocycles are also common Compounds m which sulfur is the heteroatom m three four five and six membered rings as well as larger rings are all well known Two interesting heterocyclic compounds that contain sulfur-sulfur bonds are hpoic acid and lenthiomne... 

The name of the parent six membered sulfur containing heterocycle is thiane It is num bered beginning at sulfur Multiple incorporation of sulfur in the ring is indicated by the prefixes di tri and so on... 

The various possibilities for the first two types of syntheses are listed schematically in Table 4, and the possibilities for synthesis from other heterocycles are listed in Table 5. In each case the method is discussed in more detail in the following sections Tables 4 and 5 indicate the section(s) in which a particular reaction is described. In the case of sulfur-containing heterocycles, 5-oxides and 5,5-dioxides are treated alongside the basic parent structures, since for 1,3,2-dioxathiolane, 1,2,3-oxadithiolane, and 1,2,5-oxadithiolane the unoxidized rings are unknown. 

Examples of 47i electrocyclization and related ring openings in oxygen-and sulfur-containing heterocycles have been widely reported. The effect of substituents on the ease of photocyclization of 1-benzoxepins (1) to cyclo-buta[b]-l-benzofurans (2) has been studied.3 1,3-Dioxepin (3) is readily converted to 2,4-dioxabicyclo[3.2.0]hept-6-ene (4) on irradiation in diethyl... 

E. Kleinpeter, Conformational Behaviour of Six-Membered Rings (E. Juaristi, ed.), VCH, New York (1995) Conformational Analysis of 6-Membered Sulfur-Containing Heterocycles, p. 201. 

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