L,2-Dithiol-3 Ones

Mercaptodithiole thiones 93 were treated with sulfur monochloride and DABCO under conditions for the synthesis of tricyclic bis-dithiolothiazines from substituted diisopropylamines (see Scheme 38). Unexpectedly, in all the cases 5-chloro-l,2-dithiole-3-ones 96 were formed in high yields (2006RCB143 Scheme 47). 

H. Behringer and E. Meinetsberger, Thiophene derivatives and 1,2-trithiones from l,2-dithiol-3-one /7-toluenesulfonylhydrazones and desaurins. Tetrahedron Lett. 1915 (1973). 

Grignard reagents commonly react at S(2) of l,2-dithiole-3-ones with ring opening (Scheme 18) (73LA247, 74LA1261, 82AHC(31)63>. 

Halogen atoms in cationic olium rings are very reactive. The halogen atom in the quaternary salts of 3- and 5-halo-1-phenylpyrazoles is replaced at 80-100°C by hydroxy, alkoxy, thiol, amino or cyano groups (66AHC(6)347). 3-Halo-1,2-dithiolyliums are converted into l,2-dithiol-3-ones by water and react readily with other nucleophiles (80AHC(27)l5i). 

A related reaction is the cycloaddition of l,2-dithiole-3-ones 80 onto a number of electrophilic alkynes such as acetylenedicarbaldehyde or its monoacetal. It affords different stable thials or thiones372 (equation 83). 

Phosphorus oxychloride reacts with l,2-dithiol-3-ones, giving 3-chloro-l,2-dithiolium ions. If this reaction is carried out in the presence of an active methylene compound, a condensation follows immediately, giving a dithiolylidene derivative. For instance, 5-phenyl-l,2-dithiol-3-one reacts with phosphorus oxychloride and benzoylacetonitrile, giving benzoyl-(5-phenyl-l,2-dithiol-3-ylidene)-acetonitrile (Eq. 10).29... 

The 1,2-dithiole system and related compounds possess two adjacent sulfur atoms in a five-membered ring. The types are known respectively as 1,2-dithiolanes (1), 1,2-dithioles (2), l,2-dithiol-3-ones (3a), l,2-dithiole-3-thiones (3b), 3-iminodithioles (3c), l,2-dithiol-3-ylidenes (3d) and 1,2-dithiolylium (4) ions. 

The spectra of a large number of l,2-dithiol-3-ones (3a) and l,2-dithiole-3-thiones (3b) have been tabulated (64MI43100). l,2-Dithiol-3-one itself shows two maxima at 226 and 310 nm, and l,2-dithiole-3-thione has four maxima at 229, 251, 336 and 415 nm. Neither of these compounds shows much solvent effect. 

Studies on l,2-dithiol-3-ones (3a) show carbonyl absorptions around 1640-1670cm-1 ... 

Dithiolanes (1), in contrast to other dithioles, are not planar. In the carboxylic acid (28a) the CSSC dihedral angle is 26.6° (B-61MI43100), leading to a strain of 67 kJ mol-1. These compounds are unstable and the parent may be obtained only in dilute solution. Lipoic acid (29) is more stable, but does polymerize. The instability may account for its particular reactivity (B-61MI43101). l,2-Dithiol-3-ones (3a) and -3-thiones (3b) are very stable, as is evident from their modes of formation. Simple l,2-dithiol-3-imines (3c) are also stable, but some readily interconvert to isothiazoline-3-thiones (30) (Section 4.31.3.2). 

Several thieno[3,2-6]thiophenes (67) are produced by pyrolysis of various 1,2-dithioles, including bi(l,2-dithiol-3-ylidenes) (20), alkali metal salts of l,2-dithiole-3-sulfonyI hydrazides (68) (75TL3473), and tetrahydrobenzo-l,2-dithiol-3-ones (69) (63BSF161). 

AIkoxy l,2-dithioles (34a) and bis(l,2-dithiol-3-yl) ethers (36a) are pseudobase forms of 1,2-dithiolylium salts, which they regenerate on acidification (65JCS32). However, the dithiole (113) readily loses sulfur to form an acyclic product (114). Like the l,2-dithiole-3-thiones (3b) below, l,2-dithiol-3-ones (3a) are readily converted into 3-halo-l,2-dithiol-ylium salts (35a). 

Dithiolanes are efficiently synthesized by the oxidative cyclization of 1,3-dithiols , as illustrated by the preparation of 1,2-dithiolane 77 in quantitative yield from 1,3-propanethiol 76 by oxidation with iodine in the presence of 2-methyl-2-butene (Scheme 44) <20000L369> and a similar synthesis of the l,2-dithiol-3-one 78 (Scheme 45) <2004TL4307, 2006JME5626>. 

Hydrolysis of chlorinated dithiolium salts of this type (Section II, B, 3) yields chlorinated l,2-dithiol-3-ones which have recently attracted attention because of their fungicidal properties.13... 

The dissociation of 28 by path A is exemplified by the reactions of the l,2-dithiol-3-ones (30a) ( Baumann-Fromm disulfides 48) and of the trithiones (30b) with halogens. 

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