1.2- dithiones

Tliermolyses of 245-248 were investigated (83JA4519). 1,2-Dithietes 246, thermodynamically favored products in the equilibrium with their 1,2-dithione counterparts, were satisfactorily generated from 245 and their photoelectron spectra were recorded. At higher temperatures, 246 decomposed to the corresponding alkynes and S9. Meanwhile, on thermolysis of 247, the corresponding 1,2-dithiones, and not 1,2-dithietes, were formed in the cases of R = Me and Et, and their photoelectron and IR spectra were... 

As happens for dioxolenes, dithiolenes can undergo the reversible sequence 1,2-dithionej 1,2-dithione monoanion/ene-1,2-dithiolate illustrated in Scheme 6. 

On passing from the neutral 1,2-dithionate to the dianionic 1,2-dithiolate, the Ni-S and C-S distances progressively increase, whereas the C-C distance decreases. 

Several 1,2-dithiones can be obtained from 1,2-diones by direct sulfurization with P4S[0 or B2S3. The usually heterogeneous reaction can be accelerated by the use of ultrasound.24 Although most dithiones are prone to hydrolysis and decomposition (some cannot be prepared at all under the above conditions), they are most useful intermediates in the synthesis of more complex dithiolenes. 

Dithietanes 74 have been studied as appropriate sources for their valence tautomers 1,2-dithiones 75a, 75b (equation 79) and theoretical calculations have been carried... 

There are some theoretical studies concerning the stability of 1,2-dithietenes and ethane-1,2-dithiones <1996IJQ859>. The valence isomerization of a series of 1,2-dithietes 19 to the open-chain dithiones 20 was studied by CASSI multiconfiguration methods, including the CASPT2 perturbational treatment <1996IJQ859>. 

Theoretical and experimental studies on the reaction of 3,4-bis(methoxycarbonyl)-1,2-dithiete with alkenes and alkynes yielding cycloadducts have been carried out. The activation energy of the interconversion of the 1,2-dithiete to 1,2-dithione was estimated by MO calculations. These calculations (MP2/6-31G(d)) show that the dithiete 19f is 5.8 kcal mol-1 more stable than the ethane-1,2-dithione cis-20f, and the tautomerization energy is 28.5 kcal mol-1 from the thiete 19f and this value of the activation energy supports the possibility of the tautomerization between the 1,2-dithiete 19f and ethane-1,2-dithione cis-20f, at least at high temperature <1996IJQ859>. 

Dithiete, the smallest unsaturated cyclic system with a disulfide bond, has been the subject of interest since 1960 because of its structure, unique bonding properties, and relation to its valence isomer, ethane-1,2-dithione. 

The reaction of 1,2-dithietes with unsaturated compounds has also been investigated. 1,2-Dithietes were found to react with alkenes and alkynes to give the cycloadducts stereospecifically, which indicates the concerted reaction between ethane-1,2-dithione, the valence isomer of 1,2-dithiete, and dienophiles <2000JOM(611)106, 1999JOC8489>. 

It was suggested that this reaction proceeds via the biradical 129 or 1,2-dithione as-20f, which is generated as tautomer of 19f (Scheme 15) <2000JOM(611)106>. 

In an attempt to prepare the 1,2-dithione (41), 4,6-dihydro-4,4,6,6-tetramethylfuro[3,4-d]-l,2,3-thiadiazole (37) was treated with molten sulfur, yielding a mixture of cyclopolysulfides. Subsequent photolysis of this mixture in the presence of an alkene (e.g., norbornene) gave adducts such as compound (42), indicating the intermediacy of the dithione (41) (87TL4833). 

F. From 1,2-Dithiones, Including Dithiaoxamides and Esters of Tetrathiaoxalate / 23... 

In this chapter, the term dithiolene refers to a ligand of the formula R2C2S2, which depending on one s formalism could be described as an alkene-1,2-dithiolate dianion, a 1,2-dithione, or some oxidation state between these two extremes (Fig. 1). Benzenedithiolates, their derivatives, and analogues are also included. 

II. SYNTHESIS FROM PREFORMED ALKENEDITHIOLATES, 1,2-DITHIONES, AND THEIR EQUIVALENT... 

Few dithiolenes are prepared via reactions involving 1,2-dithioketones, a rare class of compounds prone to oligomerization. The first stable 1,2-dithione, l,2-bis(4-dimethylaminophenyl)ethane-l,2-dithione, was generated by photolysis... 

A subset of the 1,2-dithiones are dialkyl tetrathiooxalate esters, C2S2(SR)2. The parent C2S2(SMe)2 exists in dynamic equilibrium with its dimer (Eq. 15) (179). 

Dithiolene complexes display unusual structural, electronic, photophysical, photochemical, and reactivity features. The base ligand units, 1,2-ethenedithio-late, 1,2-dithione, and 1,2-benzenedithiolate, are depicted in Scheme 1 as A, B, and C. 

Figure 1. Valence bond description of the various dithiolene ligand forms. Two-electron oxidation of the dianionic ene-1,2-dithiolate results in the formation of the 1,2-dithione and 1,2-dithiete resonance forms.

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