Acetals N-bromosuccinimide

Dihydroxy-16 methyl-4,9(11 )-pregnadiene-3,20-dlone 21 Acetate N-Bromosuccinimide Perchloric Acid... 

Acetals N-Bromosuccinimide. f-Bulyl hydroperoxide. Dimethylboron bromide. Na-fion-H. Organocopper reagents. Organoti-tanium reagents. Titanium(IV) chloride. 

More recently, Santoyo Gonzdlez and co-workers [43] reported the Hofmann rearrangement of amide 84 into cyclic carbamate 85 (40% yield. Scheme 24). This was achieved with a mixture of mercuric acetate, N-bromosuccinimide and N,hr-dimethylformamide. 

Bromination has been described using brominating agents such as N-bromosuccinimide in carbon tetrachloride (418. 420) bromine in either chloroform, acetic acid, or hydrochloric acid (414. 418, 421-423) bromine in sulfuric acid (415-417) and enzymatic catalysis (424, 425). 

Preparation of 9a-Bromo-110,17a 1 Trihydroxy-16 -Methyl-4-Pregnene-3,20-Dione 21-Acetate To a mixture of 620 mg of 17a,21-dihydroxy-16/3-methyl-4,9(11 )-pregnadiene-3,20-dione 21-acetate and 330 mg of N-bromosuccinimide in 10 ml of dioxane and 3.2 ml of water cooled to 10°C was added 1.8 ml of cold 1 M aqueous perchloric acid. The mixture was stirred at 15°C for 3 hours. Excess N-bromosuccinimide was destroyed by addition... 

Bromo pyruvaldoxime Methotrexate N-Bromosuccinimide Betamethasone acetate Bromocriptine Medrogestone 2-Bromothiophene Thihexinol... 

Residual N-bromosuccinimide from the manufacturing process may be identified and/or quantified by making use of its oxidation potential by titration of liberated iodine after addition of potassium iodide in acetic acid (25). 

Halogenation of dibenzofuran produces the 2-halo compounds. Bromina-tion can be achieved in good yield with bromine in acetic acid " or with N-bromosuccinimide in boiling carbon tetrachloride. The 2,8-dibromo compound has been made, using dioxane dibromide. Chlorination of dibenzofuran in acetic acid in the presence of iron powder can be controlled to yield the 2-chloro or the 2,8-dichloro compounds. 2-Chlorodi-benzofuran is best prepared by reaction of dibenzofuran with phosphorus pentachloride. 2-Iododibenzofuran (45%) results from treatment of dibenzofuran with iodine in boiling chloroform in the presence of nitric acid. 2,8-Diododibenzofuran is best prepared by reaction of dibenzofuran with iodine and iodic acid in aqueous acetic acid. ... 

Our initial work on the TEMPO / Mg(N03)2 / NBS system was inspired by the work reported by Yamaguchi and Mizuno (20) on the aerobic oxidation of the alcohols over aluminum supported ruthenium catalyst and by our own work on a highly efficient TEMP0-[Fe(N03)2/ bipyridine] / KBr system, reported earlier (22). On the basis of these two systems, we reasoned that a supported ruthenium catalyst combined with either TEMPO alone or promoted by some less elaborate nitrate and bromide source would produce a more powerful and partially recyclable catalyst composition. The initial screening was done using hexan-l-ol as a model substrate with MeO-TEMPO as a catalyst (T.lmol %) and 5%Ru/C as a co-catalyst (0.3 mol% Ru) in acetic acid solvent. As shown in Table 1, the binary composition under the standard test conditions did not show any activity (entry 1). When either N-bromosuccinimide (NBS) or Mg(N03)2 (MNT) was added, a moderate increase in the rate of oxidation was seen especially with the addition of MNT (entries 2 and 3). 

The isomerization of allyl ethers to 1-propenyl ethers, which is usually performed with potassium tert-butoxide in dimethyl sulfoxide, can also be carried out under milder conditions using tris(triphen-ylphosphine)rhodium chloride,208 and by an ene reaction with diethyl azodicarboxylate,209,210 which affords a vinyl ether adduct. Removal of an O-allyl group may be achieved by oxidation with selenium dioxide in acetic acid,211 and by treatment with N-bromosuccinimide, followed by an aqueous base.201,212... 

Dissolve 71 g. of p-methylnaphthalene in 450 g. (283 ml.) of A.R. carbon tetrachloride and place the solution in a 1-litre three-necked flask equipped with a mechanical stirrer and reflux condenser. Introduce 89 g. of N-bromosuccinimide through the third neck, close the latter with a stopper, and reflux the mixture with stirring for 16 hours. Filter off the succinimide and remove the solvent under reduced pressure on a water bath. Dissolve the residual brown oil (largely 2-bromomethyl naphthalene) in 300 ml. of A.R. chloroform, and add it to a rapidly stirred solution of 84 g. of hexamine in 150 ml. of A.R, chloroform contained in a 2-litre three-necked flask, fitted with a reflux condenser, mechanical stirrer and dropping funnel maintain the rate of addition so that the mixture refluxes vigorously. A white solid separates almost immediately. Heat the mixture to reflux for 30 minutes, cool and filter. Wash the crystalline hexaminium bromide with two 100 ml. portions of light petroleum, b.p. 40-60°, and dry the yield of solid, m.p. 175-176°, is 147 g. Reflux the hexaminium salt for 2 hours with 750 ml. of 50 per cent, acetic acid, add 150 ml. of concentrated hydrochloric acid, continue the refluxing for 5 minutes more, and cool. Extract the aldehyde from the solution with ether, evaporate the ether, and recrystallise the residue from hot w-hexane. The yield of (3-naphthaldehyde, m.p. 59-60°, is 50 g. 

Monosubstitution at a occurs in 255 with N-bromosuccinimide, N-chlorosuccinimide, and 25% nitric acid at 0° disubstitution (a a ) occurs with bromine or chlorine in acetic acid, thionyl chloride, chlorosulfonic acid, and 70% nitric acid and tetrasubstitution (a a bb ) is obtained with 90% nitric acid 254b behaves similarly. Tetra-cyanoethylene forms -complexes with 255 and 328,340 and the latter compound is slowly converted on standing to a C-substituted derivative with loss of HCN. 

A most useful route leading regioselectively to 6-bromo-6-deoxy derivatives involves the treatment of pyranosidic 4,6-O-benzylidene acetals with N-bromosuccinimide [18]. An acyl group is produced in the 4-position (Scheme 3) [19]. 

In the final stages, the benzylidene acetal was again opened by the action N-bromosuccinimide, and subsequent reduction and deacylation steps were accomplished as before to yield the target a glycoside. 

Table I. Reaction of O-Benzylidene Acetals with N-Bromosuccinimide... 

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