[17534-15-5]  · C6H6S2  · Benzene-1,2-dithiol  · (MW 142.24)

(starting material for the preparation of several organosulfur reagents)

Physical Data: mp 27-28 °C; bp 119-120 °C/17 mmHg; d 1.236 g cm-3.

Form Supplied in: deliquescent, bad-smelling solid; commercially available. Aged samples may be contaminated by polymeric disulfides.

Preparative Methods: can be prepared by a number of methods.1,2

Handling, Storage, and Precautions: to be kept refrigerated under an inert gas.

The thiol groups of benzene-1,2-dithiol react with a number of reagents to afford compounds of good synthetic potential.

Acyclic Reagents.

The S,S-dimethyl derivative of the title reagent has been oxidized to the corresponding chiral bis-sulfoxide, which can be viewed as a bifunctional aryl methyl sulfoxide (eq 1).3

Five-Membered Rings.

The carbon atom between the two sulfur atoms in benzodithioles can be activated as a carbocation (1), carbene (2), or carbanion (3).

1,3-Benzodithiolium salts (1)4 are useful for numerous functional group transformations. For example, 1,3-benzodithiolium tetrafluoroborate reacts rapidly with Trimethyl Phosphite in the presence of Sodium Iodide to give 2-(O,O-dimethylphosphonyl)-1,3-benzodithiole. This reagent can be used in Horner-Emmons reactions with various carbonyl compounds for the preparation of benzo-1,4-dithiafulvenes (eq 2).5a The double bond of the latter can be hydrogenated under mild conditions and the benzenedithiol eventually removed to generate the aldehyde.5b The sequence corresponds to a one-carbon homologation of carbonyl compounds. Other applications include the preparation of 1D-aldehydes,5c the reduction of sugars,5d and the transformation of many carboxylic acid derivatives (eq 3).5e 2-Phenyl-1,3-benzodithiolium trifluoromethanesulfonate can be used to convert alcohols into benzyl ethers and benzoates under mild conditions (eq 4).6

Treatment of the benzenedithiolium tetrafluoroborate with base is one method for generating 1,3-benzodithiole-2-ylidene (2).7 The carbene is also formed as an intermediate in the 1,3-dipolar cycloaddition of carbon disulfide with benzyne.4 It displays a 6p-electron system and belongs to the class of nucleophilic carbenes capable of reacting with sulfur and selenium metal.4c

1,2-Benzenedithiol has found much use in the synthesis of organic metals. A large number of electron-rich compounds have been synthesized with the aim of producing conducting radical cation salts.8 (4), (5) and (6) are representative compounds derived from the dithiol.

The ability of the two sulfur atoms in benzodithioles to stabilize a negative charge (unlike the parent 1,3-dithiolane that fragments on treatment with bases) makes these reagents useful as umpoled formyl and acyl anion synthons.9 As with many other sulfur reagents of this type, the oxides exhibit higher reactivity, but the anion of the tetroxide gives aldol-type products only with difficulty because of its stability. The trans dioxide of 1,3-benzodithiole can be transformed via a Mannich reaction into the 2-methylene derivative which exhibits dienophilic properties and high diastereoselection in Diels-Alder cycloadditions (eq 5).10

A number of heteroatoms can be included in the five-membered ring in between the two sulfur atoms. Examples include phosphorus11 and boron.12 The latter compound has been shown to catalyze Diels-Alder reactions. A large number of complexes of 1,2-benzenedithiol are also well-known and are currently being investigated.13

Six-membered Rings.

1,4-Benzodithiin S,S,S,S-tetroxide is available from 1,2-benzenedithiol or by other methods.14 These compounds exhibit exceptional reactivity as dienophiles, higher than the bis(phenylsulfonyl)ethylenes (see 1,2-Bis(phenylsulfonyl)ethylene; 1,1-Bis(phenylsulfonyl)ethylene). The 2-chloro derivative can be used as C2 synthon in cycloaddition reactions for the preparation of molecules that are difficult to prepare by other methods (eq 6).15

Seven and Higher-Membered Rings.

Sulfur in liquid ammonia is used in one method of synthesis of benzopentathiepine (eq 7).16a This sulfide can be used in the synthesis of heterocycles and as a sulfur transfer reagent.16b Benzo-1,3,5,2,4-trithiadiazepine is a 10p aromatic system available from benzene-1,2-dithiol via the bis-sulfenyl chloride shown in eq 8.17 Higher ring systems (thiocrown heterocycles) can also be prepared.18

1. (a) Hurtley, W. R. H.; Smiles, S. JCS 1926, 1821. (b) Backer, H. J.; Wiggerink, G. L. RTC 1941, 40, 470.
2. (a) Hünig, S.; Fleckenstein, E. LA 1970, 738, 192. (b) Ferretti, A. OSC 1975, 5, 419. (c) Degani, I.; Fochi, R. S 1976, 471. (d) Maiolo, F.; Testaferri, L.; Tiecco, M.; Tingoli, M. JOC 1981, 46, 3070. (e) Block, E.; Eswarakrishnan, V.; Gernon, M.; Ofori-Okai, G.; Saha, C.; Tang, K.; Zubieta, J. JACS 1989, 111, 658. (f) Giolando, D. M.; Kirschbaum, K. S 1992, 451.
3. Bendazzoli, P.; Di Furia, F.; Licini, G.; Modena, G. TL 1993, 34, 2975.
4. (a) Campbell, C. D.; Rees, C. W. JCS(C) 1969, 742, 748, 752. (b) Nakayama, J. S 1975, 38. (c) Nakayama, J.; Sugiura, H.; Hoshino, M. TL 1983, 24, 2585.
5. (a) Degani, I.; Fochi, R. S 1977, 263. (b) Barbero, M.; Cadamuro, S.; Ceruti, M.; Degani, I.; Fochi, R.; Regondi, V. G 1987, 117, 227. (c) Ceruti, M.; Degani, I.; Fochi, R. S 1987, 79. (d) Prasad, J. S.; Clive, D. L. J.; da Silva, G. V. J. JOC 1986, 51, 2717. (e) Degani, I.; Fochi, R. JCS(P1) 1978, 1133.
6. Mocerino, M.; Stick, R. V. TL 1990, 31, 3051.
7. Scherowsky, G.; Weiland, J. LA 1974, 403.
8. For example: (a) Mizuno, M.; Cava, M. P. JOC 1978, 43, 416. (b) Bryce, M. R. JCS(P1) 1985, 1675.
9. (a) Ager, J. D. In Umpoled Synthons; Hase, T. A. Ed.; Wiley: New York, 1987; pp 19-72. (b) Gimbert, Y.; Moradpour, A.; Bittner, S.; Jordis, U. TL 1989, 30, 819. (c) Boyd, D. R.; Sharma, N. D.; Dorman, J. H.; Dunlop, R.; Malone, J. F.; McMordie, R. A. S.; Drake, A. F. JCS(P1) 1992, 1105.
10. Aggarwal, V. K.; Lightowler, M.; Lindell, S. D. SL 1993, 730.
11. (a) Chen, C. H.; Donatelli, B. A.; Zumbulyadis, N. S 1978, 667. (b) Sau, A. C.; Holmes, R. R. JOM 1978, 156, 253.
12. Howarth, J.; Helmchen, G.; Kiefer, M. TL 1993, 34, 4095.
13. Holm, R. H. CSR 1981, 10, 455.
14. (a) Wenkert, E.; Broka, C. A. Finn. Chem. Lett. 1984, 126. (b) Nakayama, J.; Nakamura, Y.; Hoshino, M. H 1985, 23, 1119.
15. De Lucchi, O.; Cossu, S. CC 1992, 1089.
16. (a) Sato, R.; Saito, S.; Chiba, H.; Goto, T.; Saito, M. BCJ 1988, 61, 1647. (b) Sato, R.; Chino, K. TL 1991, 32, 6345.
17. Morris, J. L.; Rees, C. W. JCS(P1) 1987, 211.
18. (a) Kyba, E. P.; John, A. M.; Brown, S. B.; Hudson, C. W.; McPhaul, M. J.; Harding, A.; Larsen, K.; Niedzwiecki, S.; Davis, R. E. JACS 1980, 102, 139. (b) Sundermeyer, J.; Roesky, H. W.; Noltemeyer, M. CJC 1989, 67, 1785.

Ottorino De Lucchi & Fabrizio Fabris

Università di Venezia, Italy

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