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Pyrroles substitution regioselectivity

The regioselectivity of substitution in pyrrole and thiophene is like that of furan and for similar reasons... [Pg.508]

In the tris-pentafluorophenyl analog (TFPC), in contrast to other Co corroles, aromatic amines can substitute PPh3 to form six-coordinate trivalent bis(amine) complexes.788 Bis-chlorosulfon-ation of TFPC occurs regioselectively to give the 2,17-(pyrrole)-bis-chlorosulfonated derivative fully characterized as its triphenylphosphinecobalt(III) complex.789 The amphiphilic bis-sulfonic acid was also obtained. [Pg.69]

The influence of substituents on regioselectivity was studied by using a model nitrone 3,4-dihydro-2,2-dimethyl-2/f-pyrrole 1-oxide (DMPO, 256) with different alkylidenecyclopropanes substituted with phenyl (156), electronreleasing (270 and 271) and electron-withdrawing groups (52, 272 and 4) [67,... [Pg.46]

Electrophilic substitutions at the pyrrole nucleus were described only with 1,2-dihydropyrrolizines which react with the same regioselectivity as would do equivalently substituted monocyclic pyrroles. [Pg.9]

A study of the regioselectivity of the 1,3-dipolar cycloaddition of aliphatic nitrile oxides with cinnamic acid esters has been published. AMI MO studies on the gas-phase 1,3-dipolar cycloaddition of 1,2,4-triazepine and formonitrile oxide show that the mechanism leading to the most stable adduct is concerted. An ab initio study of the regiochemistry of 1,3-dipolar cycloadditions of diazomethane and formonitrile oxide with ethene, propene, and methyl vinyl ether has been presented. The 1,3-dipolar cycloaddition of mesitonitrile oxide with 4,7-phenanthroline yields both mono-and bis-adducts. Alkynyl(phenyl)iodonium triflates undergo 2 - - 3-cycloaddition with ethyl diazoacetate, Ai-f-butyl-a-phenyl nitrone and f-butyl nitrile oxide to produce substituted pyrroles, dihydroisoxazoles, and isoxazoles respectively." 2/3-Vinyl-franwoctahydro-l,3-benzoxazine (43) undergoes 1,3-dipolar cycloaddition with nitrile oxides with high diastereoselectivity (90% de) (Scheme IS)." " ... [Pg.460]

Regioselective synthesis of 2-substituted pyrroles using oximinocyanoacetate esters or related compounds in a Knorr-type reductive condensation with diketones was described . Thus, oximinocyanoacetates 63 reacted with pentane-2,4-diones 64 in hot... [Pg.242]

As described in the previous sections, a variety of nucleophiles attack the Cy atom of ruthenium-allenylidene intermediates. Aromatic compounds should also be suitable candidates and this was found to be the case [30]. Thus, reactions of propargylic alcohols with heteroaromatic compounds such as furans, thiophenes, pyrroles, and indoles in the presence of a diruthenium catalyst such as la proceeded smoothly to afford the corresponding propargylated heteroaromatic compounds in high yields with complete regioselectivity (Scheme 7.25). The reaction is considered to be an electrophilic aromatic substitution if viewed from the side of aromatic compounds. [Pg.233]

Large 1-alkyl substituents increase 3-substitution in the Vilsmeier formylation of pyrroles (70JCS(C)2573). A similar trend occurs in trifluoroacetylation of W-alkylpyrroles (80JCR(S)42). The trifluoroacetylation, formylation and bromination of 1-tritylpyrrole occur regioselectively at the 3-position in high yield (83JCS(P1)93). [Pg.304]

MO calculations67 on the trimethylsilylation of pyrrole and IV-alkylpyrroles have been reported in full and studies of sulfonation by S03 also pursued. Suggestions are made to reconcile the predictions as to regioselectivity with the experimentally observed /3-substitution in the reactions. [Pg.199]

Facile, regioselective ring opening-cross-metathesis reactions between unsymmet-rical norbornene derivatives and electron-rich alkenes in the presence of the second-generation Grubbs catalyst have been reported to generate highly substituted furans and pyrroles.114... [Pg.308]

Notice that the three key reactions work brilliantly in this synthesis the hydrogenation of 113 is totally stereoselective and very high yielding while the two electrophilic substitutions on the pyrrole are perfectly regioselective acylation of 108 controlled by steric hindrance and alkylation of 112 controlled by electronic preference and because it is intramolecular. [Pg.324]

The preceding sections describe regioselective electrophilic addition of pyrrole complexes at the 3-position with various electrophiles to give ( -substituted lZ/-pyrrole or 3//-pyrrolium isomers. The latter compounds, in contrast to their noncomplexed counterparts, are only moderately acidic (pKa 6) and therefore resist rearomatization and multiple alkylations. For example, when uncomplexed 2,5-dimethylpyrrole is treated with 1 equiv of methyl acrylate and TBSOTf, a statistical 1 2 1 ratio of starting material, monoalkylated 105 (vide infra), and 3,4-bis-alkylated product is found.12 Treatment of 1-methylpyrrole under the same conditions results in at least four alkylated products along with starting material. In contrast, coordination by osmium results in smooth... [Pg.19]

Several 2-substituted 3,4-diarylpyrroles 3 have been prepared in a regioselective process employing the base induced addition of methyl isocyanoacetate to the a,f -unsaturated nitriles 4, and one of the pyrroles so obtained was used in a concise synthesis of the alkaloid ningalin B... [Pg.141]

Notice that the regioselectivity is the same as it was with pyrrole—the 2-position is more reactive than the 3-position in both cases. The product ketones are less reactive towards electrophiles than the starting heterocycles and deactivated furans can even be nitrated with the usual reagents used for benzene derivatives. Notice that reaction has occurred at the 5-position in spite of the presence of the ketone. The preference for 2- and 5-substitution is quite marked. [Pg.1160]

Intramolecular acylations of pyrroles and indoles are useful synthetically, for example, A-glutamyl-substituted pyrrole 94 gives 95, regioselectively, with retention of configuration, on brief treatment with methanolic hydrogen chloride or boron tribromide. A seven-membered ketone 97 was produced from 96 no cyclization onto the indole 4-position was observed <1999T4341>. [Pg.406]

An enantioselective radical substitition (termed SOMO activation ) involving pyrroles has been reported <07SCI582>. For example, treatment of pyrrole 58 with octanal 59 and chiral amine 60 in the presence of CAN gave chiral 2-alkylated pyrrole 61. The mechanism included the formation of an enamine radical. A radical alkylation of 3-substituted pyrroles with xanthates produced 2,3-disubstituted pyrroles regioselectively <07TL4515>. [Pg.130]


See other pages where Pyrroles substitution regioselectivity is mentioned: [Pg.114]    [Pg.242]    [Pg.118]    [Pg.144]    [Pg.263]    [Pg.1010]    [Pg.82]    [Pg.145]    [Pg.117]    [Pg.242]    [Pg.412]    [Pg.408]    [Pg.339]    [Pg.115]    [Pg.311]    [Pg.258]    [Pg.349]    [Pg.143]    [Pg.116]    [Pg.152]    [Pg.5]    [Pg.41]    [Pg.46]    [Pg.100]    [Pg.45]    [Pg.107]    [Pg.109]    [Pg.17]    [Pg.196]    [Pg.210]    [Pg.115]    [Pg.129]   
See also in sourсe #XX -- [ Pg.23 ]




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