Sulfur acid derivatives, substitution reactions

With Sulfur Nucleophiles N-Carboxy-protected aziridine-2-carboxylates react with thiols to give P-mercapto-ot-amino acid derivatives. The reaction is usually catalyzed by BF3 and the yields range from fair to excellent [15, 16, 108-111]. With N-unprotected 3-substituted aziridine-2-carboxylates, the ring-opening with thiols usually takes place with anti stereoselectivity, especially in the case of the C-3 aliphatic substituted substrates. In cases in which C-3 is aromatic, however, the stereoselectivity has been found to be a function of the substitution pattern on the aromatic ring 3-p-methoxy ph eri yl-su bs li In led aziridines 143a (Scheme 3.51) and... 

Diaryl ditellurium compounds catalyzed the oxidation of aryl-substituted olefins by /-butyl hydroperoxide, hydrogen peroxide, 3-chloroperbenzoic acid, pure oxygen, or air in the presence of sulfuric acid. When the reactions were carried out in refluxing methanol, the vic-dimethoxy compounds were obtained. With acetic acid as the reaction medium, the vic-diacetoxy derivatives were isolated, text.-Butyl hydroperoxide was the best oxidizing agent with yields approaching 100%. ... 

A variation involves the reaction of benzylamines with glyoxal hemiacetal (168). Cyclization of the intermediate (35) with sulfuric acid produces the same isoquinoline as that obtained from the Schiff base derived from an aromatic aldehyde and aminoacetal. This method has proved especially useful for the synthesis of 1-substituted isoquinolines. 

As a result of the 7r-deficiency of the pteridine nucleus, alkyl pteridines are activated in the a-positions. The common reactions based on C—H acidity are found with a wide variety of compounds. Bromination of 6- and 7-methyl groups leads to mono- and di-substitution selective formation of the monobromomethyl derivatives has not yet been achieved satisfactorily. 6-Methylisoxanthopterin is claimed to give the 6-bromomethyl derivative with bromine in acetic and sulfuric acids at 100 °C for 2 min (50ZN(B)132) and with 1,7-dimethyl-lumazine a 90% yield of the 7-bromomethyl derivative (60CB2668) is obtained after 4h... 

The range of preparatively useful electrophilic substitution reactions is often limited by the acid sensitivity of the substrates. Whereas thiophene can be successfully sulfonated in 95% sulfuric acid at room temperature, such strongly acidic conditions cannot be used for the sulfonation of furan or pyrrole. Attempts to nitrate thiophene, furan or pyrrole under conditions used to nitrate benzene and its derivatives invariably result in failure. In the... 

The first electrophilic substitution reaction studied in the isoxazole series was the nitration of 3,5-dimethylisoxazole reported by Morgan and Burgess in 1921.The reaction occurs smoothly on heating with mixed nitric and sulfuric acids at 100°C and leads to the 4-nitro derivative in 86% yield. 

Electronegative groups do not invariably prevent nuclear bromination, but reaction conditions must be much more severe, and the orientation of substitution may be affected by the substituent. Thus 6-nitroquinoline was brominated in sulfuric acid at 100°C to give the 8-bromo product (71) in 51% yield 8-methyl-5-nitroquinoline gave a 69% yield of the 7-bromo derivative (72) under similar conditions, whereas 7-chloroquinoline was transformed into the 5-bromo product (93%) (88CHE892) (Scheme 35). In a sealed tube reaction with bromine, 8-nitroquinoline gave a mixture... 

Dichloro-2,2 -dimethyl-1,1 -dianthraquinonyl can be synthesized by Friedel-Crafts reaction from phthalic anhydride and 2,6-dichlorotoluene. Subsequent cyclization of the resulting substituted benzoylbenzoic acid 102 in sulfuric acid affords the corresponding anthraquinone derivative 103, which is dimerized by Ullmann reaction ... 

Reaction of a sulfinyl sulfone with a nucleophile in the manner shown in (139) is, of course, an example of a nucleophilic substitution at sulfinyl sulfur. Reactions of this general type occur frequently and are of great importance in the chemistry of most kinds of sulfinic acid derivatives. At this point it would seem desirable to discuss what is known about such key aspects of their mechansim as stereochemistry and the timing of the bond-making and bond-breaking processes necessary in such a substitution. In doing this we will call upon results obtained from the study of such reactions using a variety of different types of sulfinic acid derivatives. 

The reactions represented by (191) are all nucleophilic substitutions occurring at a sulfonyl sulfur. Besides cpdisulfones substitutions of this kind are also of frequent occurrence in the chemistry of many other types of sulfonyl derivatives such as sulfonyl halides, aryl esters of sulfonic acids, etc., and many of the general aspects of their behaviour and mechanism have been examined in considerable detail. Most of the remainder of this section will be devoted to consideration of the results of such studies. 

Technetium dissolves in dilute or concentrated nitric acid to form nitrate, Tc(N03)2. Reaction with concentrated sulfuric acid yields the sulfate TCSO4. Technetium is oxidized by hydrogen peroxide in alkaline solution to form soluble pertechnetate, Tc04 anion. Such pertechnatate anion forms complexes with tertiary or quarternary amines, pyridine and its methyl-substituted derivatives. 

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