Bromo zinc

The gem-dibromide, MejSiCHBrj, reacts with a Zn-Cu couple in THF at 60°C to give the gem-bis(bromo)zinc compound, Me3SiCH(ZnBr)2. 

The Reformatsky reagent ethyl bromo zinc acetate added across the 3,4-double bond of quinazoline, but oxidation followed and 4-ethoxycarbonyl-methylquinazoline was formed in low yields. 

Interaction of long-chain n-alkylammonium halides with a halide of a divalent metal leads to the formation of salts of the general formula (RNH3)2MX4 with peculiar phase changes in the solid state [65]. Bis(n-alkylammonium)bromo zinc-ates with n = 10-16 display two reversible high entropy solid crystalline-solid crystalline phase transitions and a solid crystalline-liquid crystalline (smectic phase) transition up to at least 450 K. 

Reformatski reaction Aldehydes and ketones react with a-bromo- fatty acid esters in the presence of zinc powder to give -hydroxy-esters which may be dehydrated to give a-, 0-unsaturated esters. a-Chloroesters will react if copper powder is used in conjunction with the zinc. 

This preparation illustrates the Reformatsky reaction, which consists in the interaction of a carbonyl compound, an a-halogen ester (e.g., ethyl bromo-acetate) and zinc In the presence of ether or benzene, followed by hydrolysis. 

Fluorescein is obtained by condensing phthahc anhydride (1 mol) with resorcinol (2 mols) in the presence of anhydrous zinc chloride. The tetra-bromo derivative, readily prepared by the addition of the calculated quantity of bromine, is eosin. 

Bromo-2-nitrophenylacetic acid (26 g, 0.10 mol) was dissolved in a mixture of 50% HjSO (400 ml) and ethanol (600 ml) and heated to 90°C. Over a period of 1 h, zinc dust (26.2 g, 0.40 mol) was added. slowly and then heating was continued for 2 h. The excess ethanol was removed by distillation. The solution was cooled and filtered. The filtrate was extracted with EtOAc. The filtered product and extract were combined, washed with 5% NaCOj and brine and then dried (MgSO ). The solvent was removed in vacuo and the residue recrystallized from methanol to give 20.5 g (97% yield) of the oxindole. 

Deuteration at C-9 by Treatment of a 9a-Bromo-11 -keto Steroid with Zinc in Acetic Acid-OD... 

Zinc dust (35 mg) is added to a solution of 9a-bromo-5a-androstan-ll-one (225, 13 mg) in anhydrous ether (2 ml) and acetic acid-OD (0.5 ml, prepared by heating an equimolar mixture of acetic anhydride and deuterium oxide) and the resulting suspension is stirred at room temperature for 4 hr. (The progress of the reaction can be checked by thin layer chromatography.) The... 

Deuteration at C-9 by treatment of a 9a-bromo-ll-keto steroid with zinc in acetic acid-OD, 204... 

Reductive opening with zinc and isopropanol or acetic acid is possible either at the bromo ether stage or at the a,/5,-unsaturated keto... 

Kitazume and Kasai [55] have investigated the Reformatsky reaction in three ionic liquids. This reaction involves treatment of an a-bromo ester with zinc to give an a-zinc bromide ester, which in turn reacts with an aldehyde to give an addition product. An example is given in Scheme 5.1-26. Moderate to good yields (45-95 %) were obtained in ionic liquids such as [EDBU][OTf] for the reactions between ethyl bro-moacetate or ethyl bromodifluoroacetate and benzaldehyde [55]. 

Similar reactions were also carried out with 3-bromopropene, l-bromo-2-butene, 3-bromocy-clohcxcnc. and 3-bromocyclooctene in refluxing ethanol as solvent24 . Zinc-mediated Barbier reactions can be accomplished with high yields in a mixture of saturated aqueous NH4C1/THF (5 1), at room temperature or below using a 1.2 to 2-fold excess of the halide over the carbonyl compound25. 

To a stirred solution of 110 mg (0.246 mmol) of benzyl (3S,5S,6/f)-3-bromo-2-oxo-5,6-diplienyl-4-morplio-linecarboxylate in 2 mL of dry tilt is added 150 tL (0.944 mmol) of trimcthyl(2-propenyl)silane followed by addition of 2.5 mL of a 0.187 M solution of zinc chloride in THF (0.472 mmol). After stirring for 60 h at 25 "C the mixture is poured into water and thoroughly extracted with CH,CL. The combined extracts... 

The chemistry of indium metal is the subject of current investigation, especially since the reactions induced by it can be performed in aqueous solution.15 The selective reductions of ethyl 4-nitrobenzoate (entry 1), 2-nitrobenzyl alcohol (entry 2), l-bromo-4-nitrobenzene (entry 3), 4-nitrocinnamyl alcohol (entry 4), 4-nitrobenzonitrile (entry 5), 4-nitrobenzamide (entry 6), 4-nitroanisole (entry 7), and 2-nitrofluorenone (entry 8) with indium metal in the presence of ammonium chloride using aqueous ethanol were performed and the corresponding amines were produced in good yield. These results indicate a useful selectivity in the reduction procedure. For example, ester, nitrile, bromo, amide, benzylic ketone, benzylic alcohol, aromatic ether, and unsaturated bonds remained unaffected during this transformation. Many of the previous methods produce a mixture of compounds. Other metals like zinc, tin, and iron usually require acid-catalysts for the activation process, with resultant problems of waste disposal. 

Alkylzinc halides have also been prepared under microwave irradiation. The Reformatsky reagents (2-t-butoxy-2-oxoethyl)zinc bromide and [(2-dibenzylamino)-2-oxoethyl]zinc bromide were synthesized from the corresponding bromides via reaction with zinc in THF (Scheme 5) [24], The oxidative addition was executed at 100 °C in 5 min. The obtained reagents were subsequently used in Negishi reactions on 2-bromopyridine, 3-bromopyridine, 2-bromo-5-nitropyridine, and 2-bromo-5-trifluoromethyl-pyridine using Pd(PPh3)4 as a catalyst (Scheme 5). 

Cholest-3-ene has been prepared previously by deamination of 5/3-cholestan-3 -yl amine,by reduction of a mixture of 4 -bromo-5 -cholestan-3a-ol and its epimer with zinc in acetic acid, and as component of a mixture of cholestenes by Wolff-Kishner reduction of cholest-4-en-3-one. ... 

Reaction of 47 with NBS in carbon tetrachloride afforded the tribromide (240, 100%). After replacement of the primary bromo group with benzoyl-oxyl, the product (241,47%) was debrominated with zinc dust in ethanol to give the diene (242,64%). Epoxidation of242 produced the isomeric compounds 243 and 244, which were transformed into the azides (245 and 246), convertible into valienamine isomers. ... 

These examples show that when information is not needed to identify the compound, it is omitted from the name. In the first name, for instance, it is not necessary to tell how many sodium ions are present, because we can deduce the number from the name of the complex anion. In the second name, the oxidation state of zinc is omitted because it is always +2. In the fourth name, the single bromo ligand is not preceded by the prefix mono. 

The reaction of an a-halo carbonyl compound with zinc, tin, or indium together with an aldehyde in water gave a direct cross-aldol reaction product (Eq. 8.90).226,227 A direct Reformatsky-type reaction occurred when an aromatic aldehyde reacted with an a-bromo ester in water mediated by zinc in low yields. Recently, it was found that such a reaction mediated by indium was successful and was promoted by son-ication (Eq. 8.91).228 The combination of BiCl3-Al,229 CdCl2-Sm,230 and Zn-Et3B-Eb0231 is also an effective mediator. Bismuth metal, upon activation by zinc fluoride, effected the crossed aldol reaction between a-bromo carbonyl compounds and aldehydes in aqueous media. The reaction was found to be regiospecific and syn-diastereoselective (Eq. 8.92).232... 

Reaction of p-fluorobenzyl chloride with the anion of diethylmethylmalonate ester followed by saponification and decarboxylation leads to acid 9. Polyphosphoric acid cyclization leads to indanone 10. A Reformatsky reaction with zinc amalgam and bromo-acetic ester leads to carbinol 11 which is then... 

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