Synthesis of Thioamides and Thiolactams

Schaumann, Ernst

doi:10.1016/b978-0-08-052349-1.00163-3

Cited by 24 publications

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“…[10] The parallel product hydrogen sulfide is the most probable candidate for the reducing agent (Scheme 3). The reduction of a thiocarbonyl group to a sulfide unit is exceptional; thioamides usually serve as thioacylating agents [11] or, in the presence of another adjacent thiocarbonyl group, may be reduced to a methylene group. [12] p-Chlorophenyl isocyanate (3b) and p-nitrophenyl isocyanate (3c) were found to react quite rapidly with 2 in diethyl ether to provide good crude yields of 6b,c.…”

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The Reaction of Cyanothioformamide with Isocyanates − Formation of a Disulfide by Reduction of a Thiocarbonyl Group

2001

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Keywords: Thioamides / Isocyanates / Cyclizations / ImidazolidinesThe reactions of the title compounds are governed by sulfur redox chemistry. Thus, cyanothioformamide 2 reacts with aryl isocyanates 3a−c to give bis[3-aryl-1-(arylcarbamoyl)-2-oxo-4-(arylcarbamoylimino)imidazolidin-5-yl] disulfides 6, as shown by an X-ray crystallographic investigation of product 6a. Reaction with methyl isocyanate (3d) gives the related The reactions of N-substituted cyanothioformamides with electrophiles have provided a number of interesting heterocyclic ring closures. [2Ϫ5] In particular, their reactions with isocyanates [4] and isothiocyanates [5] give 1,3-disubstituted imidazolidine systems 1 (Scheme 1). In order to determine the scope of these reactions and to evaluate a possible route to the 1-unsubstituted analogs (R 1 ϭ H), it was deemed of interest to study similar reactions using the unsubstituted cyanothioformamide 2. This compound was first prepared in 1815 by Gay-Lussac [6] from cyanogen and hydrogen sulfide; in fact, it provided one of his examples for establishing the law of combining proportions. In the intervening 185 years, only about 20 references to this compound have appeared in the chemical literature, none of which has explored its synthetic utility. We have found that the conventional synthesis of 2 from 1 equiv. each of cyanogen and hydrogen sulfide [7] can be improved by using diethyl ether as a solvent and by adding triethylamine (4) as a catalyst, and that the crude product can best be crystallized from dichloromethane/pentane. Scheme 1 [ ‡] Heterocyclic Ring-Closure Reactions, Part XI. Ϫ Part X: Ref. [1] [a]1695 trisulfide 7d along with disulfide 6d. A desulfurized product, imidazolinone 10, could also be isolated from the methyl isocyanate reaction and was characterized by X-ray diffraction analysis. In boiling ethanol, 6a and 7d undergo reductive desulfurization to give 4-iminoimidazolidin-2-one 11a and the methyl analog 11d, respectively.We first treated 2 with phenyl isocyanate (3a) in diethyl ether, using amine 4 as a catalyst. The crude product, obtained in good yield, was found to melt over a wide temperature range. However, repeated recrystallization gradually provided a single, higher melting product, combustion analysis of which was consistent with it being a 3:1 adduct of 3a and 2. This composition suggested that the product might have had the imidazole structure 5a, derived from the sequence of reactions shown in Scheme 2.Scheme 2 However, that this structure was incorrect was indicated by a signal at δ ϭ 6.6 in the 1 H NMR spectrum, by the fact that the mass spectrum showed a peak at m/z ϭ 2 [M ϩ 1], and by the lack of color of the product, which was inconsistent with the presence of an intact thiocarbonyl group. Thus, we carried out an X-ray crystallographic analysis, which revealed (Figure 1) that the product was apparently derived from 5a by reduction to the dimer 6a. The molecule has an almost planar imidazolidine ring and this plane also includes the double-bonded heteroatoms O21 an...

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