Sulfur-amino rearrangement

Nitraminothiazole. treated for 12 hr with 96% sulfuric acid, gives 2-amino-5-nitrothiazole (194). The mechanism of this rearrangement is not yet quite resolved even for nitraminobenzene derivatives (617). The series of kinetic determinations and appropriate labeling performed by Toth et al. provide, however, precious hints for this difficult problem (1578. 1579). 

In the first case (22), almost stoichiometric amounts of sulfuric acid or chlorosulfonic acid are used. The amine sulfate or the amine chlorosulfate is, first, formed and heated to about 180 or 130°C, respectively, to rearrange the salt. The introduction of the sulfonic acid group occurs only in the ortho position, and an almost quantitative amount of l-aminoanthraquinone-2-sulfonic acid is obtained. On the other hand, the use of oleum (23) requires a large excess of SO to complete the reaction, and inevitably produces over-sulfonated compound such as l-amino-anthraquinone-2,4-disulfonic acid. Addition of sodium sulfate reduces the byproduct to a certain extent. Improved processes have been proposed to make the isolation of the intermediate (19) uimecessary (24,25). 

The converse situation in which ring closure is initiated by the attack of a carbon-based radical on the heteroatom has been employed only infrequently (Scheme 18c) (66JA4096). The example in Scheme 18d begins with an intramolecular carbene attack on sulfur followed by rearrangement (75BCJ1490). The formation of pyrrolidines by intramolecular attack of an amino radical on a carbon-carbon double bond is exemplified in Scheme 19. In the third example, where cyclization is catalyzed by a metal ion (Ti, Cu, Fe, Co " ), the stereospecificity of the reaction depends upon the choice of metal ion. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Chemists at the Naval Air Warfare Center (NAWC), Weapons Division, China Lake, have reported many examples of polynitroarylamine synthesis via Bamberger rearrangements of arylnitramines. " " The nitration of 4-amino-2,5-dinitrotoluene (36) with a mixture of nitric acid and acetic anhydride in glacial acetic acid at room temperature yields the nitramine (37) which on treatment with neat sulfuric acid, provides 4-amino-2,3,5-trinitrotoluene (38) as the sole product. " Nitration of 3,4-dinitroaniline (39) with a solution of nitric acid in acetic anhydride yields A,3,4-trinitroaniline (40) acid-catalyzed rearrangement of the latter in neat sulfuric acid furnishes a 74 % yield of isomeric 2,3,4- (41) and 2,4,5- (42) trinitroanilines in a 4 6 ratio.Accordingly, a mixture of products can be expected when an unsymmetrical arylnitramine has two unsubstituted ortho positions available. 

Numerous carbacyclic, or sulfur-containing, analogues of mono- and difluoronucleo-sides have been synthesized as potential antivirals. In the carbacyclic series, the starting compound is hydroxymethylcyclopentene oxide. Rearrangement of this oxirane creates a new unsaturation that can be oxidized further into another epoxide. An amino function can then be introduced on the 4 position and can be used to build the base (Figure 6.13). 

Nitration of 4-amino-6-methylpyridazin-3(2-ff)-one at C-5 was performed in two steps. Treatment with concentrated nitric acid affords 6-methyl-4-(nitroamino)pyridazin-3(2f/)-one whose rearrangement in concentrated sulfuric acid led to the formation of 4-amino-6-methyl-5-nitropyridazin-3(2/0-one <2001RJ01026>. 

For the retro-Dimroth rearrangement of a TP, apparently only one example has been found (70JPR254) 5-Amino-6-cyano-TP (24) under the influence of the unusual rearranging agent concentrated sulfuric acid leads to [4,3-a] derivative 25 (Scheme 12). The triazole ring is believed to be polyprotonated in this medium and to have its most nucleophilic site at N-4. 

In the synthesis of a-amino acids [290] through addition of the carbanion of MMTS to nitriles the overall process involves three other steps frequently encountered in sulfur-mediated chemistry a Pummerer-type rearrangement, with a less common migration of a methylthio group, and a Raney nickel desulfurization following transesterification of the thioester function. 

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