1.2- Dithiole-3-thiones and l -dithiol-3-ones

Dithiole-3-thiones and l,2-dithiol-3-ones will not be treated in separate sections in this survey, as very few papers dealing with l,2-dithiol-3-ones... 

A linear correlation of H and C shifts of adjacent ring positions and between the ring and some substituents in 1,2-dithiol-3-ones (2a), 1,2-dithiole-3-thiones (2b), and 1,2-dithiolium ions (3), indicated that the changes in the electron distribution in the ring were responsible for the shift effects <87PS(29)187>, and C NMR spectroscopy was used to confirm the structure of the l,2-dithiolo[l,2-ajdiium ion (5) <89G617>. 

With the help of TLC on silica gel G, Mayer et al. [54] have investigated many heterocyclic sulphur compounds of the trithione (I) (1,2-dithiol-3-thiones) and dithione (II) (l,2-dithiol-3-ones) types, their anils (III), the l,2-thiazoline-5-thiones (IV) and xanthane hydride (V). Petrol ether-benzene (50 + 50) or carbon disulphide are good solvents. 

The adducts formed by mercury(Il) acetate and l,2-dithiole-3-thiones are of particular interest because they are often used for converting 1,2-dithiole-3-thiones into l,2-dithiol-3-ones. The difference in the behavior of mercury(II) halides and acetate toward dithiolethiones suggests that a special mechanism operates in the latter case, probably a concerted cyclic reaction as indicated in Scheme 10. The 3-acetoxy-l,2-dithioliumcation thus obtained is rapidly converted to the corresponding dithiolone by reaction of the acetate anion or water. 

Sulfines 80 were obtained from the thermolysis of lithium salts of tosylhy-drazones of l,2-dithiol-3-ones (79) in the presence of oxygen.134 A series of these S-oxides was obtained by oxidation of l,2-dithiole-3-thiones with one equivalent of peracid under conditions where the S-oxide precipitates. Further addition of peracid gave the 1,2-dithiolylium salt (811.134 The sulfines can be prepared from m-chloroperbenzoic acid in 30-70% yields and with sodium periodate as an oxidant.135 Oxidation with reactive reagents such as (Ph0)3P03, 03, NaOCl, benzoyl peroxide, and HgO gave l,2-dithiol-3-one via the sulfine.135... 

The infrared spectra of a series of 1,2-dithiole-3-thiones have been studied and five types of IR bands were located and assigned.272 Electron delocalization in l,2-dithiol-3-ones of the type shown in Scheme 7 was discussed on the basis of IR frequencies of the carbonyl absorption and dipole moments.273 These parameters suggest that ionic structures contribute rather strongly to the structure of l,2-dithiol-3-ones. 

For l,2-dithiole-3-ones and 3-thiones, the sulfurization of various unsaturated esters to 1,2-dithiole-3-ones, and with phosphorus pentasulfide to 3-thiones is a very versatile method. It is less applicable to 5-unsubstituted types, although the parent l,2-dithiole-3-thione can be made from tetramethoxypropane and phosphorus pentasulfide <77S802>. l,2-Dithiole-3-thiones (2b), including compounds lacking 5-substituents, can be made by sulfurization of 3-substituted propanes or propenes, but the harsh conditions of this reaction render it unsuitable for many types. 

Spectroscopic data for l,3-dithiole-2-thiones and l,3-dithiole-2-ones and their corresponding saturated compounds have been compiled <81JPR737>. Calculated electron densities have been correlated with observed C chemical shifts for the benzo-1,3-dithiolylium ion <77CLI133>. 

Some years later, the first stable thiocarbonyl ylides 9 and 10 were prepared by the reaction of thiourea with cyano-substituted oxiranes (19,20) or by addition of Rh-di(tosyl)carbenoid to benzo-l,2-dithiole-3-thione (21), respectively. Enhanced stability and the low reactivity of 9 and 10, which enables their isolation in crystalline form, results from the push-pull substitution at the two termini [cf. also (22)]. Another class of stable thiocarbonyl ylides that are also able to afford [3 + 2]-cycloaddition products are the mesoionic 1,3-dithiole-4-ones of type 11 (23,24). 

Alkyl- and aryl-1,2-dithiol-3-ones (3a) are made by ring synthesis from unsaturated esters (B-66MI43100) and alkylation of these affords 3-alkoxy-l,2-dithiolylium salts (35b). The parent (3a R1 = R2 = H) is best made from the thione (3b) by treatment with mercury(II) acetate (63CB2702). 

Quantum mechanical calculations for the 1,3-dithiolylium ion, benzo-1,3-dithiolylium ion, l,3-dithiol-2-one and l,3-dithiole-2-thione have been carried out with the simple LCAO MO method <66AHC(7)39). According to these calculations, the lowest electron density was found at the 2-position of the 1,3-dithiolylium cation, and the C(4)—C(5) bond order corresponded approximately to that of an isolated C—C double bond. A delocalization energy of 105 kJ mol-1 has been calculated for this cation. For the benzo-l,3-dithiolylium ion it was found that nucleophilic attack should take place in the 2-position but electrophilic substitution at the 4-position. 

Density functional theory (DFT) and post-Hartree-Fock MP2 in conjunction with the B3LYP employing the 6-31G(d) basis set were used to predict structure and correlate assignments of the fundamental vibrational modes of 3/7-1,2-dithiole-3-one la and 3/7-1,2-dithiole-3-thione lb with experimental data <1998VSP77>. These sulfur-rich heterocycles, characterized by a long and weak S-S bond, are represented in accordance to the simple 7t-MO theory by resonance contributor 8, involving a cationic 67t-l,2-dithiolylium part and an anionic thiolate or olate part, and the exocyclic C=S bond is more delocalized than the C=0 bond. However, computational evidence suggests structures with localized bonds and relatively low aromatic delocalization, which is also supported by the low values of the dipole moments, that is, 3.54 D for la and 4.12 D for lb. 

In connection with studies of the 1,2-dithiole antibiotics thiolutin and holomycin it was observed that 4-acetamido-l,2-dithiol-3-one (104) is converted to thiazine 105 by sodium ethanolate.154 Compound 106 allegedly forms from 5-(tcrf-butyl)-4-neopentyl-l,2-dithiole-3-thione and trimethyl phosphite,155 but no proof was given for the structure. 

Irradiation of 4-p-tolyl-l,2-dithiole-3-thione in the presence of styrene or a-methylstyrene gave products (114) formed by addition to the thiocarbonyl group156 (Eq. 5). The diradical 113 was proposed as an intermediate. This reaction is different from the one described by Okazaki et a/.1 57,158 for 5-phenyl-l,2-dithiole-3-thione (2) and 4,5-diphenyl-l,2-dithiole-3-thione (7),... 

The preparative reduction, polarography, and cyclic voltammetry of 5-methyl-l,2-dithiole-3-thione have been studied.171 The results obtained are in agreement with a one-electron reduction of the thiocarbonyl group to a radical-anion, which could not be detected by ESR spectroscopy as it dimerizes too fast. The dimer is further reduced by a one-electron reduction to an anion in which the ring has been opened. (Scheme 12). The dianion could be isolated after methylation and was found to be identical with the compounds isolated by Maignan and Vialle by reduction with sodium sulfide.124 The dianion corresponds to the thioketonate dianion obtained by electrochemical reduction of 1,2-dithiolylium salts.172... 

The heats of formation for three l,2-dithiole-3-thiones and l,2-dithiol-3-ones indicate that the 1,2-dithiole system possesses a delocalized 7r-electron sextet.264... 

IR and Raman spectra of a series of l,2-dithiole-3-thiones and 1,2-dithiol-3-ones have been recorded and interpreted.274 Sixteen of the eighteen fundamental ring vibrations of the parent l,2-dithiole-3-thione have been observed, and most of the substituent frequencies have been assigned. 

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