N-Arylpyrrole

The powerful Buchwald-Hartwig aryl amination methodology [135-141] has been applied by Hartwig to the synthesis of N-arylpyrroles (196) [142,143]. 

The phosphorylated derivatives 92 [87] and N-arylpyrroles 93, having biological activity [88], were synthesized from 2-formylpyrroles ... 

Various para substituted poly-N-arylpyrrole polymer films were prepared and their electrochemical properties were measured. Of particular interest are the poly-N-p-nitrophenylpyrrole films which can be oxidized to produce the polypyrrole cation and reduced to produce the nitrophenyl anion. The polymer films can be repeatedly switched between the neutral, cationic and anionic forms with coulombic reversibility and with little ir-interaction between the pyrrole and the aryl ring. 

Recognizing that the conducting polypyrrole films can be chemically modified (.1,2), the phenyl substituent assumes a particularly important role because it provides a means of introducing a wide selection of functional groups into the polymer. With this objective in mind, we have prepared a series of N-arylpyrrole polymers and find the thin poly-N-(p-nitrophenyl)pyrrole films of particular interest because they combine the electroactive properties of nitrobenzene and polypyrrole. With this combination, the polymer can be switched electrochemically between the cationic, neutral, and anionic form. 

A -Arylketenimine, 259 Arylmethylenemalondialdehyde, 180 2-Arylmethylene-l-tetralinthione, 217 Arylnitroso compound, 72-78 N-Arylpyrrole, 21-22, 73-74 A1-Aryls ulfiny limine. 259 Arylthienium salt, 233 4-Aryltriazolinedione, 159 N-Arylvinylketenimine, 259 Azabutadiene, 239-299... 

It has been known for over 30 years that IV-aryldihydrothiazine oxides, when treated with alkali under vigorous conditions, afford N-arylpyrroles [Eq. (21)]. ... 

The doubt on the origin of chirality was still perceptible in (31JA3519). Achiral N-arylpyrroles 311 and 312, as we can say now, were submitted to brucine resolution, an attempt affording optically inactive acids. Resolution of chiral N-arylpyrroles 313 and 314 failed due to the weakness of the carboxylic acid on the pyrrole ring. Nevertheless, it was stated that the optical isomerism in phenyl pyrroles probably resembles closely that in the diphenyl series. ... 

Treatment of alkyne 5 with silver acetate induced an oxidative cyclization to provide N-arylpyrrole 6 in excellent yield. The reaction was applied successfully in the total synthesis of alkaloids ( )-harmicine and ( )-crispine A (13ARK(ii)6). 

Photochemical [2 + 2] cycloaddition is a powerful way to produce cyclobutanes, which, in turn, are reactive synthesis intermediates. N-Methylpyrrole adds aldehydes via [2 -I- 2] photocycloaddition to give transient oxetanes with high regioselectivity Ring-opening produces 3-(oi-hydroxyalkyl)pyrroles which are oxidized easily to 3-arylpyrroles, such as 3-BUTYROYL-l-METHYL-PYRROLE. With a special apparatus, ethylene is conveniently added to 3-methyl-... 

Preferential hydrogenation of the heterocyclic ring of N- and C-arylpyrroles and of indoles and isoindoles is usual, but hydrogenation over Raney nickel can also lead to the... 

Reaction of aryl methyl ketoximes (118) with vinylchloride in the KOH (5-fold molar excess)/DMSO system at 120°C and atmospheric pressure gave 2-arylpyrroles (119) and their N-vinyl derivatives (120) (Scheme 58) (84KGS1359, 84MI3 87KGS1486). 

In the reaction with 1,2-dichloroethane in KOH/DMSO (100-125°C), aryl methyl ketoximes form 2-arylpyrroles (129) in 70% yield (Scheme 64). The maximum yield of simultaneously formed N-vinylpyrroles (130) and diethers (131) does not exceed 12 and 21%, respectively (86ZOR492). 

The TOSMIC anaiog -(tosyl)benzyl isocyanide readily reacts with simple acceptors (ethyl acrylate, acrylonitrile, etc.) to give 4-substituted 2-arylpyrroles. Extension to 2,3-diaryl derivatives by use of styryl acceptors required the use of n-butyllithium as a base. <95SC795>... 

Two unique type Had syntheses of pyrroles that were reported both involved cyclopropane fragmentations. The first allowed for a synthesis of 2-arylpyrroles <06SL2339>. In the event, treatment of stannylcyclopropane 25 with n-BuLi followed by benzonitrile produced 2-phenylpyrrole 26 via tin-lithium exchange, addition to the nitrile, ring fragmentation of ketimine intermediate, intramolecular condensation, and loss of dibenzylamine. 

An unusual formation of A-arylpyrroles was observed upon thermolysis of N-(4-aiylsulfenylbut-2-ynyl)anilines that was accompanied by elimination of a benzenethiol unit100. Mass-spectral rearrangements of A-propynylanilines and related compounds were studied more recently101,102. 

Pyrrole itself tends to give tars under radical conditions, probably by way of initial N-hydrogen abstraction, but some A -substituted derivatives will undergo preparatively useful arylations, with attack taking place predominantly at an a-position. More efficient routes to arylpyrroles depend on transition metal-mediated coupling processes (see section 2.7.2.2). A -Methylpyrrole is attacked by electrophilic benzoyloxy radicals at its a-positions. ... 

Lu employed a phosphine-catalyzed [3-1-2] cycloaddition of methyl 2,3-butenedioate (8) with aromatic or heteroaromatic N-tosylimines 9 to afford the N-tosyl-3-pyrrolines 10 in good yields <97TL3461>. Aromatization of these substrates to the corresponding 2-arylpyrrole-3-carboxylates 11 is effected by dehydrogenation with DDQ in refluxing benzene. 

S93> The lithium anion adds to N-tosylimines to generate 3-(benzotriazolylmethyl)propargylsulfonamides. In hot ethanolic sodium ethoxide these undergo cyclocondensation to the 2-arylpyrroles. The cyclization evidently occurs via allenic isomers formed under the basic conditions. The synthesis can also be adapted to... 

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