Sulfur—nitrogen bonds

Formation of the Nitrogen-Sulfur Bond 3.6.1 Oxidation of Thioamides... 

A related work by Nakamura et al. was recently reported to show the gold-catalyzed process of aminosulfonylation, the formal addition of a nitrogen-sulfur bond to an alkyne moiety, and environmentally benign synthesis of a wide variety of 3- and 6-sulfonylindoles, present in many biologically active compounds [120]. 

Bromide and iodide ions are not only effective as redox catalyst in the indirect electrochemical formation of carbon-hetero atom bonds but also of hetero-hetero atom bonds. Thus, the nitrogen-sulfur bond in sulfenimides (Eq. (53) Table 4, No. 33) and sulfenimines (Eq. (54) Table 4, No. 34) can be generated. The electrogenerated active bromine species forms a positively polarized sulfenyl intermediate from disulfides. 

In contrast, the thiophenone (204) undergoes a stereospecific conrotatory photocyclization via the enol (205) to give cis fused dihydrobenzo[b] thiophen (206).165 Initial nitrogen-sulfur bond homolysis is believed to be responsible for the photoisomerization of isothiazol-3(2//)-ones to thiazol-2(3//)-ones.166... 

The nitrogen-sulfur bond in 161 (X = S, R = NPhth X = S02, R = OMe) is easily broken under certain conditions. For instance, attempts to obtain a palladium-catalyzed carbonylation reaction with the iodide gave only the ring-opened disulfide 162 and the sulfonic acid 163, presumably by reductive cleavage of the N-S bond by the triphenylphosphine in the reaction mixture <2000T5571>. 

B. Preparation of Isothiazoles Involving Oxidative Formation of a Nitrogen-Sulfur Bond. 3... 

Few examples of photochemical transformations of the 10n heterocycles in this series have been reported. Notable is the conversion of thieno[2,3-c]isothiazoles (33) to thiophenes (37) by homolytic cleavage of the nitrogen-sulfur bond (Scheme 4). The enedithione (34) which arises from the initial diradical may undergo (a) cyclization via the bicyclic thiirane (35) or (b) electrocyclization to the 1,2-dithiine (36) <88H(27)2539>. Since similar rearrangements do not occur with isothiazoles, benzoisothiazoles, or the isomeric thieno[3,2-d]isothiazoles, this unique transformation is a direct consequence of the thieno[2,3-c]annelation. However, substituent effects on the efficiency of the transformation have not been explored. 

The nitrogen-sulfur bond in reduced forms of 1,2,5-thiadiazole is much less stable than in the aromatic form. The reduced systems are readily hydrolytically desulfurized to the open-chain NCCN portion of the ring (80JPR273,690PP255, 69T4277). Mesoionic thiadiazoles are also sensitive to basic hydrolysis (81JCS(P1)1033). 

The orientation of the carbonyl group has to be unambiguous, which can be parallel or antiparallel to the nitrogen-sulfur bond. Other orientations are energetically less favored because of the missing mesomeric stabilization with the amide nitrogen. 

In A-tosylcarboxamides there would be a competition in the reductive cleavage of the radical anion between the carbon-nitrogen bond and the nitrogen-sulfur bond in DMF containing acetic acid the sulfinate is reductively split off. The yeld of deprotection is highest when a mercury electrode is used [262]. 

The formation of nitrogen-sulfur bonds, as in the synthesis of sulfenimides and sulfenimines [173], and phosphorous-sulfur bonds [174] is achieved by electrolyses of activated N-H and P-H compounds in the presence of an RSSR/Br mixture ... 

Sultams may be prepared by cydisation of the appropriate aminosulfonic acids and derivatives the ring closure involves nitrogen-sulfur bond formation. The method can be applied to the synthesis of p-sultams, y-sultams and 8-sultams examples are the syntheses of (173) and (174) (Scheme 72). Modifications of the procedure include aminolysis of the corresponding sultones, and oxidation of... 

Sultams, e.g. (187)-(189), suffer hydrolysis by treatment with acid or alkali. The reaction opens the sultam ring (Scheme 78). With acids, the hydrolysis involves initial protonation of the nitrogen atom followed by nucleophilic attack by X". In alkaline hydrolysis, the reaction involves nucleophilic attack by OH and subsequent cleavage of the nitrogen-sulfur bond (Scheme 78). The order of reactivity of sultams towards hydrolysis is p>y>8. This is to be expected since it parallels the relative instability of the ring systems, where the four-membered ring is more reactive than the five and six-membered rings. 

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