1,3-Dithioles, mesoionic

Analogously, the mesoionic jV-methyl thiazol-5-ones and l,3-dithiol-4-ones afforded A-methyl-4-pyridones and thiapyran-4-ones when reacting with diphenyl cyclopropenone and its thione261. Benzonitrile oxide apparently gives a 1,3-dipolar cycloaddition to the C=0 group of diphenyl cyclopropenone rationalizing the formation of triphenyl-l,3-oxazin-6-one 41626i ... 

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). 

For mesoionic 1,2-dithioles, IR studies indicate that the cyclic structure (249) is favored over acyclic structure (250) except where R is an amino substituent (87PS(3l)109). 

Photochemical rearrangement of some mesoionic 1,3-dithioles (160) and (161) produces the dithioles (162) and (163) (80CA(92)19766l), and 4,5-dimercapto-l,3-dithiole-3-thione (164) salts are reported to rearrange to 4,5-dimercapto-l,2-dithiole-3-thione (165) salts (77EGP124044). 

This chapter deals with 1,3-dithiole compounds such as 1,3-dithiolylium ions (1), mesoionic l,3-dithiol-4-ones (2), 1,3-dithioles (3), 1,3-dithiolanes (4) and the tetrathiaful-valene system (5). During the last 15 years the chemistry of 1,3-dithiole compounds has developed considerably. One reason is that tetrathiafulvalene and its derivatives serve as donors in organic charge-transfer salts which exhibit the electrical properties of quasi-one-dimensional metals. For the preparation of such organic metals, 1,3-dithiolylium cations serve as useful synthetic intermediates. 

The mesoionic l,3-dithiol-4-ones of type (2) are best represented as resonance hybrids of several limiting formulae (2a)-(2e), of which (2a) and (2b) are presumably most representative both formulae are, for example, in good agreement with the direction of the dipole moments. According to the IUPAC nomenclature rules, the mesoionic 1,3-dithiolones (2) should be named as l,3-dithiolylium-4-olates (B-79MI43202). 

This section is divided into reactions of fully unsaturated rings like 1,3-dithiolylium ions, mesoionic 1,3-dithiolones, l,3-dithiol-2-ones and l,3-dithiole-2-thiones, and reactions of the saturated 1,3-dithiolanes. As a consequence of the positive charge in 1,3-dithiolylium ions, the main reactions of this class of compounds consist of nucleophilic attack at the 2-position, whereas the mesoionic 1,3-dithiolones undergo cycloaddition reactions. Reactivity of the benzo ring in benzo-l,3-dithiole and related systems has not been studied to any extent. 

Examples of these systems are the l,2-dithiole-3-thione 43 and the type A mesoionic l,3-thiazolium-4-olate 44. Important members of this class are the tetrathiafulvalenes (TTFs) 45 and related systems, which have been studied extensively because of their potentially useful electrical properties . 

Reactivity of 1,3-Dithiolium Ions Mesoionic 1,3-Dithiol-4-ones, -4-thiones 1,3-Dithiol-2-ones, -2-thiones... 

Reactivity of Substituents Attached to Ring Carbon Atoms. 7.1 Substituents Attached to Mesoionic 1,3-Dithiol-4-ones, -4-thiones, -4-selenones. 7.2 Substituents Attached to 1,3-Dithiole. 7.3 Substituents Attached to 1,3-Dithioianes. 8 Reactivity of Substituents Attached to Ring Heteroatoms. 9 Ring Syntheses from Acyclic Compounds Classified by Number of Ring Atoms Contributed by Each Component. 9.1 1,3-Dithioiium Ions... 

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. 

In this section, 1,3-dithiolium ions, mesoionic l,3-dithiol-4-ones, and 4-thiones are discussed. Reactivity of 1,3-dithiol-2-ones (X=0) and 2-thiones (X=0) is also reported here on the grounds that ionic canonical structures 94b-e make the 1,3-dithiole ring fully conjugated . 

In the reviewed period, most work was connected with synthesis of 1,3-dithioles and 1,3-dithiolanes. Only a few contributions on the synthesis of 1,3-dithiolium ions, mesoionic l,3-dithiol-4-one and -thione derivatives were reported during this time. 

This section deals with the synthesis of 1,3-dithiole and 1,3-dithiolane rings. No investigations on ring synthesis of 1,3-dithiolium ions and mesoionic 1,3-dithiole derivatives were reported in this category. 

A number of publications of substantial significance have appeared in literature since the preparation of this chapter up to October 2007. These concerned mostly 1,3-dithiolanes, 1,3-dithioles and TTF systems. No new investigations were reported on 1,3-dithiolylium ions, mesoionic 1,3-dithiol-4-ones and mesoionic l,3-dithiole-4-thiones. 

With tetrachloro-o-benzoquinone 1,2-benzodithiolethione gives a spirane (163).236 4-Phenyl-l,2,4-triazoline-3,5-dione forms mesoionic compounds (e.g., 164) with l,2-dithiole-3-thiones.237-238... 

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. 

Dithiolium salts react with hydrazines similarly to amines, but further cyclization gives pyrazoles (46) or pyrazolium salts (47). When there are replaceable substituents, hydrazones and azines are formed. A mesoionic l,2-dithiole-3-olate (20 R = Ph) reacts similarly at C(3) with aniline, but with eventual formation of the products (48) and (49) <87CJC2830,92T8127). The reaction... 

Dithioles with hydroxy and thiol substituents are protonated forms of l,2-dithiole-3-ones (2a) and -3-thiones (2b) respectively, which are regenerated on deprotonation. The reactions with nucleophiles of 3-alkoxy and 3-alkylthio-1,2-dithiolium salts give dealkylation products only in minor amounts. Instead, nucleophilic attack occurs on the ring (Section 3.11.4.2(iv)). A l,2-dithiolium-4-thiolate (98) readily acylates on an amine function to form a l,2-dithiolo-l,2-dithiole (99). This unusual reactivity is explained by the relative preferences for cyclic and acyclic forms of mesoionic forms <91EGP293120>. 

REACTIONS OF 1,3-DITHIOLYLlUM IONS, MESOIONIC 1,3-DITHIOL-4-ONES,... 

IJ-Dithiolylium Ions, Mesoionic 1 J-Dithiol-4-ones, and 1,3-Dithioles... 

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