Nitrogen-sulfur bond, cleavage

Sultams like (190) undergo aminolysis with amines by nitrogen-sulfur bond cleavage (similar to hydrolysis), and suitably functionalised sultams (191) may also suffer carbon-nitrogen bond cleavage by a bimolecular (E2) elimination reaction (Scheme 79). 

Nitrogen sulfur bond cleavage The deprotection conditions for the amine products of tert butylsulfinamide are HCl in MeOH or MeOH/dioxane, 25 °C. 

However, when the chlorosulfonation of the dichlorobenzenesulfonanilides 369 was carried out at 50-60 °C, the conditions successfully used in the chlorosulfonation of the analogous dichlorobenzoic acid anilides, nitrogen-sulfur bond cleavage occurred to yield the corresponding dichlorobenzenesulfonyl chlorides 371 (Equation 116). 

Other side reactions that have been reported are cleavage of the carbon-nitrogen bond to form 24 and an aminyl radical 25 or scission of the tliiocarbonyl-sulfur bond to form a thiyl radical 26 and 27 (Scheme 9.I0). U 6 4 Thiocarbonyl-sulfur bond cleavage may be a preferred pathway in the case of primary dithioearbamates. 

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>. 

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. 

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]. 

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. 

Ketones containing sulfur or nitrogen atoms bound to a-carbons suffer carbon-sulfur or carbon-nitrogen bond cleavage under the conditions of the Clemmensen reduction [159, 864 (p. 118). A ketosulfone was reduced to a sulfone-alcohol with zinc in refluxing 80% acetic acid in 70% yield [920]. 

Typical examples for type 2 are the cleavage of the carbon-oxygen bond in benzylic ethers (X = OR) either directly or indirectly via triarylamine cation radicals [49] (Eq. 22.42), the cleavage of the carbon-nitrogen bond in amines (X = NR2) [50] (Eq. 22.43), and the cleavage of the carbon-sulfur bond in sulfides (X = SR) [51] (Eq. 22.44) ... 

Cleavage of a carbon to sulfur bond by a lithium reagent is a well known entry to organolithium reagents. This process has been used to synthesize a-nitrogen carbanions, and hence SMA derivatives.67 165 This study has been extended to tellurium and selenium starting materials as well.166... 

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