Dithiols from imines

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). 

Amino-l,2-dithiolium salts are obtained from either / -oxocarbox-amides or ) -oxocarbonitriles by reaction with phosphorus penta-sulfide, followed by addition of perchloric acid (Scheme 6). These cations, which may also be considered as iminium salts, are deprotonated to the corresponding l,2-dithiol-3-imine by ammonia. ... 

The reactions of alkynes, alkynoic esters, ynamines, and dehydrobenzene with l,2-dithiole-3-thiones (2b), and occasionally l,2-dithiol-3-imines (12c), has been extensively studied <82AHC(3i)63>. The initial products for thiones are 3-thioacylmethylene-l,3-dithioles or thiazoles (111), which can react further to form di- or tri- adducts (113) and (114) respectively. Other rearrangements can give trithiapentalenes (6). Thials, formed from reactions of 5-unsubstituted-l,2-dithiole-3-thiones, can dimerize to products (112) with loss of sulfur (Scheme 14). Similar types of reactions have been observed with l,2-dithiole-3-thiones (2b) reacting with alkenes and ketenes, especially under... 

Methylthio-l,2-dithiolium perchlorates may be obtained directly from keten mercaptals, for example (31), by the action of phosphorus pentasulphide and subsequent treatment of the insoluble residue with perchloric acid. Similar treatment of /3-keto-amides (32) yields 3-arylimino-l,2-dithiole perchlorates (27 R = Ar, X = CIO4). The method succeeds with amides (32 R = alkyl) and thus serves as a route to the previously inaccessible 5-alkyl-l,2-dithiol-3-imines. Demethylation of 3-methylthio-5-phenyl-l,2-dithiolium cation, to give 3-phenyl-l,2-dithiole-3-thione, occurs when the iodide is heated in xylene. 

The formation of an isothiazole ring from the thiophene system (5) is of interest. Probably ammonia breaks the sulfur-carbonyl bond and then adds to the second carbonyl group, giving an imine (8), which is then oxidized by the hydrogen peroxide. A number of similar rearrangements and interconversions of isothiazole, thiophene, and dithiole systems are known and will be discussed later (Section II,C,3). 

Addor s synthesis of the hydrochlorides of the benzoisotrithione imines from benzene-1,2-dithiol and cyanogen chloride has already been discussed in detail (Section III, A, 1, a). 

The products from the reaction of aryl amines with the l,2-dithiole-3-thione-Br2 complex have been described both as imines (83)139,140 and as isothiazolin-5-thiones (84).141 142... 

However, definitive evidence for the existence of the title compounds has been given by Tamagaki and Oae, who recently reported the isolation of the compounds (112), obtained from the reaction of l,2-dithiole-3-thiones with bis(toluene-p-sulphonyl)diazomethane. The reaction of l,2-dithiole-3-thiones with Chloramine T produced thiocarbonyl imines (113) in a similar manner. ... 

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