Sulfur—nitrogen bonds reactions with

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

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>. 

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. 

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). 

Various types of electron-deficient sulfur diimides react as hetero-dienophiles. In general, these cycloadditions occur under conditions similar to those used for AT-sulfinyl compounds. However, fewer types of sulfur diimides have been utilized in this process relative to Af-sulfinyl compounds. Some examples of symmetrical sulfur diimide Diels-Alder reactions are listed in Table l-II. It should again be noted that the orientational selectivity in these cycloadditions is the same as that shown by N-sulfinyl systems (cf. Table l-I). Several examples of cycloadditions with unsymmetrical sulfur diimides are shown in Table l-III. In all cases, these reactions were totally regioselective, and as noted above, reactions occurred at the least electron-deficient nitrogen-sulfur bond. Frontier molecular orbital (FMO) theory has been used to rationalize the regio-selectivity of addition of the cationic sulfur diimide shown in entry... 

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

Sulfamation is the formation (245) of a nitrogen sulfur(VI) bond by the reaction of an amine and sulfur trioxide, or one of the many adduct forms of SO. Heating an amine with sulfamic acid is an alternative method. A practical example of sulfamation is the artificial sweetener sodium cyclohexylsulfamate [139-05-9] produced from the reaction of cyclohexylamine and sulfur trioxide (246,247) (see Sweeteners). Sulfamic acid is prepared from urea and oleum (248). Whereas sulfamation is not gready used commercially, sulfamic acid has various appHcations (see SuLFAMiC ACID AND SULFAMATES) (249—253). 

The red [SSNO] anion (37) is produced by the reaction of an ionic nitrite with elemental sulfur or a polysulfide in acetone, DMF or DMSO.115 The [SSNO] anion has a planar cis structure with a short S-S distance (1.99 A), and S-N and N-O distances of 1.67 and 1.22 A, respectively. The treatment of [SSNO]- with triphenylphosphine produces the thionitrite anion [SNO]- (38) with a bond angle of ca. 120° at nitrogen and S-N and N-O bond lengths of 1.69 and 1.21 A, respectively. 

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