Pyrrole catalytic reduction

Reduction of isoindoles with dissolving metals or catalytically occurs in the pyrrole ring. Reduction of indolizine with hydrogen and a platinum catalyst gives an octahydro derivative. With a palladium catalyst in neutral solution, reduction occurs in the pyridine ring but in the presence of acid, reduction occurs in the five-membered ring (Scheme 38). Reductive metallation of 1,3-diphenylisobenzofuran results in stereoselective formation of the cw-1,3-dihydro derivative (Scheme 39) (80JOC3982). 

Sulfonamides (R2NSO2R ) are prepared from an amine and sulfonyl chloride in the presence of pyridine or aqueous base. The sulfonamide is one of the most stable nitrogen protective groups. Arylsulfonamides are stable to alkaline hydrolysis, and to catalytic reduction they are cleaved by Na/NH3, Na/butanol, sodium naphthalenide, or sodium anthracenide, and by refluxing in acid (48% HBr/cat. phenol). Sulfonamides of less basic amines such as pyrroles and indoles are much easier to cleave than are those of the more basic alkyl amines. In fact, sulfonamides of the less basic amines (pyrroles, indoles, and imidazoles) can be cleaved by basic hydrolysis, which is almost impossible for the alkyl amines. Because of the inherent differences between the aromatic — NH group and simple aliphatic amines, the protection of these compounds (pyrroles, indoles, and imidazoles) will be described in a separate section. One appealing proj>erty of sulfonamides is that the derivatives are more crystalline than amides or carbamates. 

Catalytic reduction of pyrroles gives successively A3-pyrroles and pyrrolidines. Tetrahydrofurans are formed by the catalytic reduction of furans with Raney nickel and hydrogen ring cleavage products... 

Catalytic reduction of the C-alkenyl and -alkynyl substituents over palladium or Raney nickel can be effected without concomitant hydrogenation of the heterocyclic system to give the corresponding alkyl-pyrroles and -indoles (72HC(25-2)65, B-77MI30504). 

A simple stereospecific synthesis of 1-substituted pyrrolizidines112 starts by heating jV-formyl-L-proline (89) with EP and excess acetic anhydride to give 90% of the pyrrole 91 possibly via the 1,3-dipole 90. Catalytic reduction of 91 gave 92, which was converted into 93 and 94. 

Rodrigues Pereira N, Obirai J, Nyokong T, Bedioui F (2005) Electropolymerized pyrrole-substituted manganese phthalocyanine films for the electroassisted biomimetic catalytic reduction of molecular oxygen. Electroanalysis 17(2) 186-190... 

A frequently used intermediate in pyrrolizidine syntheses is the hydroxy-alkylpyrrolidine (3). This has been prepared in an improved yield of 40% from pyrrole by Kray and Reinecke, by Grignard reaction of pyrryl magnesium chloride with trimethylene oxide, followed by catalytic reduction [Eq. (2)]. Some 20% of the product was the isomeric compound (4). Cyclization of the mixture gave the two azabicyclic derivatives (1) and (5). A similar... 

Indolizine and its simple alkyl derivatives are sensitive to light and to aerial oxidation, which lead to destruction of the ring system. Catalytic reduction in acidic solution (reduction of the indolizinium cation) selectively saturates the pyrrole ring, giving a pyridinium salt complete saturation, affording indolizidines, results from reductions over platinum. ... 

Due to its electronic conductivity, polypyrrole can be grown to considerable thickness. It also constitutes, by itself, as a film on platinum or gold, a new type of electrode surface that exhibits catalytic activity in the electrochemical oxidation of ascorbic acid and dopamine in the reversible redox reactions of hydroquinones and the reduction of molecular oxygen iV-substituted pyrroles are excellent... 

Complex (21), a Con-cyclam analogue, is very active for the reduction of N02 and NH2OH intermediates and catalyzes the complex electrochemical conversion of N03 to NH3 325 Gold electrodes modified with cobalt-cyclam incorporated in Nafion films,324 or by electropolymerization of the pyrrole-substituted cobalt cyclam (22)326 have shown catalytic activity for the reduction of nitrate in strongly basic media. 

A poly(pyrrole) film was deposited on a Pt electrode from potentiostatic conditions at 0.8 V vs Ag/AgCl. The film was colorless, its presence was verified by oxidation and reduction of the film in plain electrolyte solution. The infrared spectrum of the electrochemically prepared poly(pyrrole) is similar to the catalytically prepared films indicating the two films are structurally similar. 

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