Palladium phosphorus pentoxide

This method is very useful for the construction of 1-substituted 3,4-dihydroisoquinolines, which if necessary can be oxidized to isoquinolines. A P-phenylethylamine (l-amino-2-phenylethane) is the starting material, and this is usually preformed by reacting an aromatic aldehyde with nitromethane in the presence of sodium methoxide, and allowing the adduct to eliminate methanol and give a P-nitrostyrene (l-nitro-2-phenylethene) (Scheme 3.17). This product is then reduced to the p-phenylethylamine, commonly by the action of lithium aluminium hydride. Once prepared, the p-phenylethylamine is reacted with an acyl chloride and a base to give the corresponding amide (R = H) and then this is cyclized to a 3,4-dihydro-isoquinoline by treatment with either phosphorus pentoxide or phosphorus oxychloride (Scheme 3.18). Finally, aromatization is accomplished by heating the 3,4-dihydroisoquinoline over palladium on charcoal. 

Isoquinoline synthesis Bischler-Napieralski synthesis is used to synthesize isoquinolines. (3-phenylethylamine is acylated, and then cyclodehy-drated using phosphoryl chloride, phosphorus pentoxide or other Lewis acids to yield dihydroisoquinoline, which can be aromatized by dehydrogenation with palladium, for example in the synthesis of papaverine, a pharmacologically active isoquinoline alkaloid. 

Bis[triphenylphosphanc] bis-[2-thiopheneteUuroIato]dlpalladium3 Under nitrogen, 1.15 g (1 mmol) of tctrakis[triphenylphosphane]palladium are dissolved in 50 ml of anhydrous benzene, a benzene solution of 0.42 g (1 mmol) of bis[2-thicnyl] ditellurium is added, the mixture is stirred under nitrogen overnight, and then filtered. The brown solid is washed with diethyl ether and dried over phosphorus pentoxide under vacuum. Addition of hexane to the filtrate precipitated additional product. 

Cyanopyrazines were previously prepared by treatment of bromopyrazines with copper(I) cyanide in refluxing 4-picoline <56JA2i4i>. These compounds can also be synthesized by palladium-catalyzed cyanation of the less reactive chloropyrazines with potassimn cyanide (Section 6.03.5.4.2). Sodium dicyanocuprate is similarly effective for the cyanation of 2-amino-3-bromopyrazine, the halogen of which is almost inert to copper(I) cyanide. Dehydration of pyrazinecarboxamides with phosphoryl chloride, acetic anhydride or phosphorus pentoxide gives the carbonitriles. 

Tank hydrogen was obtained from the Hoffman Laboratories, while the deuterium gas (99.5 %) came from the Atomic Energy Commission. They were purified by passage over platinized asbestos and by drying over phosphorus pentoxide. The ethylene was obtained from Matheson Co. and was purified by threefold condensation and distillation. Heavy ethylene CtDt was prepared by the addition of deuterium to heavy acetylene in the presence of 5 % palladium on charcoal at 0°. It is possible under these conditions to obtain a 60 % yield of C2D4. The product was brominated to separate off the ethane that was formed, and the ethylene regenerated from the nonvolatile dibromide by treatment with zinc. Any contamination of heavy acetylene was removed by absorption in alkaline mercuric cyanide solution. The mass spectrum revealed the presence of 1.6 % C2H3D. 

In the classical process a phenylethylamine reacts with a carboxylic acid chloride or anhydride to form an amide, which can be cyclised, with loss of water, to a 3,4-dihydroisoquinoline, then readily dehydrogenated to the isoquinoline using palladium, sulfur, or diphenyl disulfide. Common cyclisation agents are phosphorus pentoxide (P Ojq), phosphorus oxychloride and phosphorus pen-tachloride. The electrophilic intermediate is very probably an imino chloride, or phosphate the former have been isolated and treated with Lewis acids when they are converted into isonitrilium salts, which cyclise efficiently to 3,4-dihy-droisoquinolines. ... 

Under high pressures and temperatures, iodine reacts with oxygen to form iodine pentoxide [12029-98-0] (44). The reaction of iodine with carbon monoxide under acidic conditions is catalyzed by palladium salts (45). Phosphorous vapor and iodine react to form phosphorus triiodide [13455-01-1]> PI3 (46). 

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