1.1- Dithiolate derivatives, sulfur

A closely related route to a monocyclic dithiole derivative is shown in Scheme 122.186 The easy replacement of cobalt by sulfur in this type of process has analogy in the synthesis of a variety of condensed heterocycles from rhodacyclopentadienes (see Scheme 127 in Section IV,H,1) and cobaltacyclopentadienes (see Scheme 82 in Section IV,C,1). 

Oakley and co-workers reported the transformation of l,2,5-thiadiazolo[3,4-/ ]pyrazines into tricyclic rings 55 and 57. Titanocene 55 was prepared by reaction of 5,6-dithiol derivative 54 with Cp2TiCl2 under basic conditions (Scheme 37) <1998JA352>, and 6-amino-5-thiol 56 was condensed with sulfur monochloride to give the 1,2,3-dithiazolidine derivative 57 in excellent yield (Scheme 38) <1999JA969>. 

In [Fe(NO)(S2CNR2)2] the iron is ligated by four sulfur atoms as well as by the nitrosyl ligand similar Fe(NO)S4 chromophores are found (49) in complexes of dithiolenes (7) and dithiols (8). For both dithiolene and dithiol derivatives, reaction of [FeL2]2 (L = 7 or 8) with NO gas yields the nitrosyl derivatives [Fe(NO)L2] (50), in which the nitrosyl ligand has effected a net oxidation. Certain of the mononegative complexes can be oxidized by iodine to neutral Fe(NO)L2 or reduced with borohydride to dinegative [Fe(NO)L2]2 (50). 

There is a long standing interest in the chemistry and the properties of cyclic compounds containing sulfur atom in modern material chemistry due to their redox chemistry. In particular, the focus has been on dithiole derivatives, e.g., dithiafulvenes and tetrathiafulvalenes, since the finding of metallic conductivity and low temperature superconductivity in radical cation salts. The quite low oxidation potentials of 1,4-dithiin compounds have been reported, recently [109]. On the other hand, thioketene dimers (2,4-bis(alkyli-dene)-l,3-dithietane) have been known for more than 100 years and synthesized by various methods [110-115]. The structure of these dimer compounds is similar to that of the redox-active sulfur compounds therefore, the potential electronic property of the thioketene dimer moiety is considerably attractive with the aim of application to a new and better -donor. 

Partial oxidation of C2S4 proceeds with loss of sulfur and coupling to give the vinylidene dithiolate derivative of dmit2-. This planar dianion C4S62 is isolated as its blue-purple ELtN"1" salt (130). Treatment of this salt with metal halides affords di- and polymeric complexes, for example, [C4S6][RuCl(arene)]2 and the semiconducting [NK Seln (134) (Eq. 11). 

This chapter deals with the synthesis, reactivity, and characterization of five-membered heterocycles containing two ring sulfur atoms (1,3-dithiole derivatives) and is a review of the literature in the period 1995-2006. Previous reviews covered the literature till 1982 (CHEC(1984)) <1984CHEC(6)813> and 1995 (CHEC-II(1996)) <1996CHEC-11(3)607>. Among 1,3-dithiole compounds, 1,3-dithiolylium ions 1, mesoionic l,3-dithiol-4-ones 2, mesoionic 1,3-dithiole-4-thiones 3, 1,3-dithioles 4, 1,3-dithiolanes 5, and the tetrathiafulv alene (TTF) system 6 as a special class of compounds are discussed. 7l-Extended tetrathiafulvalenes (7t-exTTFs) containing more than one conjugated multiple bond between two 1,3-dithiole moieties are also discussed, in conjunction with 6. 

Several oxidation reactions of sulfur atoms in 1,3-dithiole derivatives were reported in the reviewed period however, no further attempts to functionalize the oxygen atoms in the products obtained were made (see Section 4.12.8). 

In this section, the reactivity of carbon- and heteroatom-containing substituents attached directly or indirectly to the heterocyclic ring of 1,3-dithiole derivatives is discussed. Here, chemical manipulations on these systems exclude ring carbon and sulfur atoms, which are the subject of Section 4.12.6. Special 1,3-dithioles called Jt-extended TTFs, containing two or more 1,3-dithiole moieties linked together via =C-(C=C) -C= or similar conjugated spacers, are discussed with typical TTFs in Section 4.12.11, although formally they constitute an example of functionalization of the 1,3-dithiole by 2rt-extended substituents, terminated by another 1,3-dithiole moiety. 

In connection with other 1,2-dithiole derivatives the ESCA spectra of l,2-dithiole-3-thiones and 5-phenyl-l,2-dithiol-3-onehave been discussed.275 In the thiones it was found that thiocarbonyl sulfur had an average binding energy near that of dithiocarboxylate sulfur. This means that a positive charge is present in the ring, i.e., mesoionic forms such as 179 must contribute considerably to the structure. The same is true for the l,2-dithiol-3-one. 

A variety of methods has been described for the synthesis of l,3-dithiole-2-thiones (233), well-known precursors for the generation of 1,3-dithiole derivatives. / -KetoW,)V-dialkyldithio-carbamates (234) are easily cyclized with cone, sulfuric acid or 70% perchloric acid to yield the corresponding 2-amino-1,3-dithiolylium salts (235), which upon treatment with hydrogen sulfide in methanol or pyridine, afford the l,3-dithiole-2-thiones (233) in excellent yields (Scheme 47) <64JOC1703, 67ZC58, 77TL2579>. 

Sulfur Addition. Since the initial studies of sulfur addition to anionic 1,1-dithiolate derivatives (Reaction 5) by Coucouvanis 14, 15)... 

The antibiotic leinamycin isolated in 1989 from a culture broth of a Streptomyces variety has a disulfide group in a 5-membered ring and thus is a 1,2-dithiole derivative. As found in stmcture 3.65, one sulfur is in the sulfide state and the other in the sulfoxide state. It has another novel feature, an 18-membered nitrogen heterocycle (in a lactam stmcture), as well as a thiazole ting. It is of considerable... 

The decomposition of diazo compounds in the presence of l,2-dithiole-3-thiones leads to 3-methylene-1,2-dithiole derivatives (79). The sulfur atom of the thione group acts as a nucleophile toward the incipient carbenic center from the diazo precursors. 

When thioketenes are generated by thermolysis or photolysis of 1,2,3-thiadiazoles, the initially formed 1,3-diradical undergoes a [3-1-3] cycloaddition to forma 1,4-dithiine derivative 9, which can extrude sulfur to produce a thiophene derivative 10. When the initially formed diradical rearranges to the thioketene it can react via a [3-1-2] cycloaddition across the 1,3-diradical to give the 1,3-dithiol derivative 11. 

Generally, unsaturated compounds, eg, alkenes and natural fats and their derivatives, are much more reactive toward sulfur than alkanes. Sulfur reacts with unsaturated compounds at temperatures of 120—215°C, forming products that are usually dark and often viscous cross-linked mixtures of dithiole-3-thiones (eq. 4) (2) and sulfides (Table 1) (3). 

A carbonyl group can be protected as a sulfur derivative—for example, a dithio acetal or ketal, 1,3-dithiane, or 1,3-dithiolane—by reaction of the carbonyl compound in the presence of an acid catalyst with a thiol or dithiol. The derivatives are in general cleaved by reaction with Hg(II) salts or oxidation acidic hydrolysis is unsatisfactory. The acyclic derivatives are formed and hydrolyzed much more readily than their cyclic counterparts. Representative examples of formation and cleavage are shown below. 

From the reactions of sulfur and carbon disulfide with cyclic ketone-derived enamines (570-573) 3H-l,2-dithiole-3-thiones were obtained, whereas the addition of carbon disulfide to other enamines gave a-dithio-pyrones (574), through initial dimerization of the enamine. 

In 2004, Dieguez et al. reported the development of novel C2-symmetric dithioether ligands derived from the corresponding binaphthyl or biphenanthryl diols. Thus, various (i )-binaphthyl dithiols substituted by alkyl groups on the sulfur atom in order to increase the steric bulk were synthesised, and the corresponding mononuclear cationic Ir(I) -cyclooctadiene complexes were prepared and characterised (Scheme 8.20). NMR studies demonstrated that, in all cases, the coordination of the ligands proceeded with complete stereoselectivity at the... 

Synthesis. These macrocycles are prepared from seven-membered ring dinitrile complexes, 84a-84c (Scheme 17), which contain either methylene, sulfur or oxygen in the five position (129). These cyclic dinitriles are synthesized by alkylating maleonitrile dithiolate or derivatives thereof with the corresponding dihalide. The dinitriles 84a-84c can be cyclized in magnesium propoxide to form porphyrazines 85a (33%), 85b (19%), and 85c (27%) (Scheme 17), which can be demetalated with trifluoroacetic to form 86a-86c. Additionally, 86a has been remetalated with nickel (87a, 92%), copper (88a, 95%), and zinc (89a, 94%). The sulfur and oxygen derivatives 85b, 85c, 86b, and 86c are of low solubility and are not suitable for further manipulation. 

Thus, the thiol sulfur may act as either a leaving group in car-tap or as an electrophile in bensultap on route to the formation of nereistoxin. Therefore, the number of nereistoxin analogs which may be prepared for insecticidal evaluation is very large. This includes the possibility of derivatives formed from the reaction between 2-dimethylamino-propane-l,3-dithiol and the chlorosulfenyl and chlorosulfinyl intermediates described in Figure 2. 

In all the reactions discussed in this section, both isopropyl groups were transformed into a 1,2-dithiole ring. When N-alkyldiisopropylamines and sulfur monochloride were mixed in chloroform in the absence of another base, that is, DABCO, two monocyclic dithiole-3-thiones 93 and 94 were isolated. 5-Mercapto derivative 93 was the main product in all the cases examined (2001MC165, 2006RCB143 Scheme 45). 

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