Bromination Sandmeyer reaction

The functional group transformation from NH2 to Br was performed with a Sandmeyer-reaction. Bromine-lithium exchange with n-BuLi (-78 °C, 12 h) and reaction with PhOPCl2 led to the phosphane 27 in 78% yield Eq. (14) [23]. 

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

Ha.loisoquinolines, The Sandmeyer reaction is commonly used to prepare chloroisoquinolines from the amino compound. The corresponding hydroxy compounds are also used by treatment with chlorides of phosphoms. The addition of bromine to a slurry of isoquinoline hydrochloride in nitrobenzene gives a 70—80% yield of 4-bromoisoquinoline [1532-97-4J. Heating 1-chloroisoquinoline [19493-44-8] with sodium iodide andhydriodic acid gives 1-iodoisoquinoline [19658-77-6] (179). 

Bromination of 136 in methanol gave the 3-bromo derivative, identical with the product of Sandmeyer reaction of the 3-diazonium salt. When the reactive 3-position was blocked, electrophilic bromination would not take place (66JOC265). Chlorination appears to occur by addition [83AHC(34)79], and perhalides are known [84MI25 90AHC(47)1]. Activating substituents are able to induce some bromination in the pyridine ring. 

Treatment of diazonium salts with cuprous chloride or bromide leads to aryl chlorides or bromides, respectively. In either case the reaction is called the Sandmeyer reaction The reaction can also be carried out with copper and HBr or HCl, in which case it is called the Gatterman reaction (not to be confused with 11-16). The Sandmeyer reaction is not useful for the preparation of fluorides or iodides, but for bromides and chlorides it is of wide scope and is probably the best way of introducing bromine or chlorine into an aromatic ring. The yields are usually high. 

Halo-de-diazoniations are a series of reactions in which the replacement of the dia-zonio group changes from a heterolytic de-diazoniation in the case of the fluorination (Balz-Schiemann reaction) to transition metal-catalyzed chlorination and bromination (Sandmeyer reaction) and finally to iodination and astatination where no catalyst is necessary due to the favorable redox potentials of I and At- (I- E° = 1.3 V). 

Amino- and 7-aminothiocoumarin have been thoroughly explored as useful precursors to a wide variety of thiocoumarins. Thus, substituents such as Cl, Br, I, SCN, CN, OH, and OMe have been introduced by way of the Sandmeyer reaction. 6-Aminothiocoumarin is brominated in the 5-posi-tion, whereby 5-bromo- or 5,6-dibromothiocoumarin may be made by way of the corresponding diazonium salt, using hypophosphorous acid or cuprous bromide, respectively. Alternatively, 6-acetylaminothiocoumarin may be nitrated in the 5-position and thus 5-nitro-, 5-amino-, 5,6-diamino-, or 6-chloro-5-nitrothiocoumarins can be prepared by classical syntheses. These derivatives are useful intermediates for the synthesis of further fused thiocoumarins (e.g., 23, 24 and 25 ). 

There appear to be no direct electrophilic substitutions of compound 2 it is unreactive toward bromine, N-bromosuccinimide, or nitrating agents.49 The sole electrophilic substitution (excluding alkylation) is that of the diazo group in compound 190 by chlorine in a Sandmeyer reaction.65 By contrast,... 

The replacement of the diazonium group by chlorine or bromine is accomplished using the Sandmeyer reaction Replacement with fluorine and iodine can be achieved by variations of this reaction. 

Bromination of [l,2,4]triazolo[4,3-a]pyridine in methanol gave the 3-bromo derivative (89), the same product obtained from the Sandmeyer reaction on 3-amino-... 

A diazonium salt reacts with copper(I) chloride or copper(I) bromide to form an aryl chloride or aryl bromide, respectively. This is called the Sandmeyer reaction. It provides an alternative to direct chlorination and bromination of an aromatic ring using CI2 or Br2 and a Lewis acid catalyst. 

Of the halogenobenzo[c]dnnolines the 1-bromo, 4-bromo, and 1,4-dibromo are obtainable by direct bromination (Section IV,B). Some, including the 2- and 3-monobromo compounds, have been prepared by the cyclization of halogenobiphenyls, - - and others, including all the monochloro and monoiodo isomers, by the photocyclization of halogenoazo-benzenes. Several have also been prepared by Sandmeyer reactions of aminobenzo [c] cinnolines. 

Amino-1,2-azoles exist as the amino tautomers. Amino-pyrazoles and amino-isothiazoles are relatively well-behaved aromatic amines, for example 3(5)-aminopyrazole undergoes substituent-A-acetylation and easy electrophilic bromination at C-4. Diazotisation and a subsequent Sandmeyer reaction provides routes to halo-isothiazoles and azido-pyrazoles. ... 

As detailed previously, Vedejs showed that trapping of 2-lithiooxazole with 1,2-diiodoethane yields 2-iodooxazole. Daugulis has demonstrated non-cryogenic conditions for the direct bromination of C2-unsubstituted oxazoles using dibromotetrafluoroethane as the electrophile. The Sandmeyer reaction can be utilized to prepare 2-chlorooxazoles from 2-aminooxazoles. Hexachloroethane can also be used as an electrophile for the direct chlorination of 2-lithiooxazole. The conversion of 2-oxazolones to 2-trifloyloxazoles is also possible however, 2-trifloyloxazoles decompose at high temperatures. ... 

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