Arylamines, reaction with sulfur

The classic syntheses of the antibacterial sulfonamides involve reaction of the appropriate arylamine with an acid addition salt of p-amino-benzenesulfonyl chloride, or p-nitrobenzenesulfonyl chloride followed by reduction. Chemical interest largely resides in preparation of the corresponding arylamines. For the synthesis of sulfacytine (134), N-ethyl uracil (131) was converted to its thioamide (132) by reaction with phosphorous pentasulfide. The newly introduced sulfur is then displaced with ammonia in methanol to give 133. Standard reactions complete... 

For the total synthesis of mukonidine (54), the required arylamine 656 was obtained quantitatively from commercial 4-aminosalicylic acid (659) using diazomethane (559). However, for large-scale preparation, this transformation was better achieved with sulfuric acid and methanol (81). The reaction of the arylamine 656 with the iron-complex salt 602 provided the iron complex 660 in 87% yield. The high yield of C-C bond formation was ascribed to the high nucleophilicity of the ortho-amino position of the aromatic nucleus arising from the hydroxy group in the 3-position of the arylamine. The iron-mediated arylamine cyclization of the complex... 

Aryldithiocarbamates (531), easily obtained by the reaction of ammonia and carbon disulfide on arylamines, are cyclized, with dehydrogenation, by heating with sulfur at 200 °C to 2-thiobenzothiazoles (532 Scheme 287). 

An industrial process for the preparation of 2-p-aminophenyl-6-methylbenzothiazole (562) (dehydrothiotoluidine) is based on the high temperature reaction of sulfur with p-toluidine (561 Scheme 297). A similar process involves the simultaneous action of sulfur and carbon disulfide on a primary arylamine. BenzothiazoIe-2-thione (564) (2-mercaptobenzothiazoIe) is synthesized industrially by reaction of aniline (563) with sulfur and carbon disulfide (Scheme 298). In this synthesis, sulfur plays the role of a dehydrogenating reagent and may be replaced by nitrobenzene. 

Reactions of sulfur compounds. AtAt-Bis(sulfonyl) arylamines lose one of the sulfonyl groups on heating with BU4NF in THF. Cyclic disulfides are obtained from 1, (o-dithiocyanotoalkanes. "... 

The A-nitroimidazolcs are stable for a time even in the presence of water, but treatment with concentrated sulfuric acid cleaves the N-nitro group, and strong base opens the ring. Much of the interest in such compounds is related to their multistep complex substitution reactions in which sequential nucleophilic addition of arylamines, ring opening, ring closure, nitroamide elimination, and rearomatization gives l-aryl-4-nitroimidazoles, e.g., 840 839. This method can also be used to prepare isotopically labeled imidazoles when labeled amino acids are used as the amine. 

For the l,2,4-dioxazol-3-one (65 R1 = Ar, X = Z = 0) (72JPR145), nucleophilic addition by secondary amines occurs at the ring C=N to give the adduct (90), and while I gives a high yield of benzamide, the site of attack in this case is less clear. In contrast, the l,2,4-dithiazole-3-thione (30) is attacked by arylamines at the thione carbon with extrusion of sulfur, in a reaction analogous to that in Scheme 15. A similar reaction occurs with the isomeric 1,2,4-dithiazolidine derivatives (41 X = 0, S) (72IJC1138). 

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