P-Bromoiodobenzene

Following the same methodology, the photostimulated reaction of the anion of 9-phenanthryl amide with ArX gave 10-aryl phenanthren-9-amines (75-100%) [51].The double arylation of 9-phenanthryl amide with p-bromoiodobenzene afforded 40% yield of the disubstitution... 

Distillation under reduced pressure gives o-bromoiodobenzene as a nearly colorless li< uid, b.p. 120 121°atl5 mm. Yield 65-75 g. (72 8.1%). 

This procedure has been utlilized successfully with a variety of aryl iodides, but aryl bromides are much less reactive. Bromoiodobenzenes and o- and p-chloroiodobenzene give the corresponding phenylenediphosphonate esters.2,3... 

Phenyl 4-(Phenyltelluro)phenyl Tellurium2 A 500-ml, three-necked, round-bottom flask is fitted with a cold-finger condenser charged with dry ice/ethanol, a nitrogen inlet, and a magnetic stirrer. 250 ml of liquid ammonia are condensed into the flask, 1.6 g (4 mmol) of diphenyl ditellurium and then pieces of sodium are added until the blue color persists. A very small amount of diphenyl ditellurium is added to discharge the blue color followed by 1.13 g (4 mmol) of 4-bromoiodobenzene, and the mixture is irradiated for 220 min. The reaction is quenched by addition of 10 ml of distilled water, the ammonia is allowed to evaporate, the residue is diluted with 100 ml of water, and the whole is extracted three times with 100 ml of diethyl ether. The extract is dried with anhydrous sodium sulfate, the solvent is distilled off, and the residue is chromatographed on neutral aluminum oxide with petroleum ether as eluent yield 0.58 g (30%) m.p. 88-907... 

However, neither copper(I) iodide nor photostimulation are absolutely necessary for the arylation of benzenetellurolate. Lithium benzenetellurolate and 1,2-bromoiodobenzene condensed in tetrahydrofuran at 20° to form 1,2-bis[phenyltelluro]benzene in 32% yield3. Sodium benzenetellurolate condensed similarly with l-chloro-2,4-dinitrobenzene at 20° in tetrahydrofuran/aqueous sodium hydroxide in the presence of a phase-transfer reagent. In this case 2,4-dinitrophenyl phenyl tellurium (m.p. 134°) was isolated in 30% yield4. Lithium methanetellurolate was arylated in tetrahydrofuran by iodobenzene5, 1,2-dibromobenzene, and l-bromo-2-methoxybenzene at 20°3. 

Since the amino group can be substituted by diazotization (p. 520), many problems of regio-selectivity can be solved by using nitro compounds as intermediates. You could, for example, use the product above to make the otherwise challenging 3-bromoiodobenzene ... 

One-pot synthesis of symmetric and asymmetric biarylacetylenes was carried out from 23 at room temperature. The TMS group in the eoupling produet 110 of p-ehloroiodobenzene was removed in situ by addition of DBU (6 equiv.) and water (40 mol%). Then m-bromoiodobenzene was added to give asymmetric diary-lacetylene in 90% yield [55]. 

Scheme 36, A and Turnover numbers up to approximately 500,000 were reported for the reaction of iodobenzene with methyl acrylate and an impressive nnmber (about 100,000) was also achieved with bromobenzene and 4-methoxy-bromobenzene. Characteristic featnres of these tridentate PCP catalysts are thermal stability and air stability. A competitive experiment, including 4-bromoiodobenzene, iodobenzene, 4-methyliodoben-zene, and 4-methoxy-iodobenzene with methyl acrylate provided a linear correlation with Hammet cr-valnes, which, however, exhibited a low p valne (1.39). It was concluded that nucleophilic aromatic substitution is not rate determining, bnt a snbsequent step with different electronic requirements, such as alkene insertion, may acconnt for this observation. Chlorobenzene could not be coupled with these catalyst. Very recently, Milstein s group reported new cyclopalladated, phosphine-free imine complexes as catalysts in the Heck arylation reaction (Scheme 36, The new dimeric imine complexes show... 

Another catalytic system was developed by Bao using the p-ketoester ligand L5 (Table 1, entry 2) [44]. Coupling of different N-nucleophiles at mild temperatures with aryliodides or bromides mainly substituted by electron-donating groups was reported. Note that reactions could be conducted at room temperature from phenyl iodide or bromoiodobenzene and pyrrohdinone. 

---