1-Imino-pyrroles

Reaction with Diazo Compounds Synthesis of 1-Imino-Pyrrole Derivatives... 

Dilithio-l,3-dienes 1 could react with diaryl diazomethanes to give multi-substituted 1-imino-pyrrole or indole derivatives 46 in high yields [73]. In this reaction, diaryl diazomethanes reacted as electrophiles. Besides, synthetic methods for Af-imino-pyrrole and indole derivatives are limited. Only when 2,3-cyclic-1,4-diphenyl-1,4-dilithio-l, 3-butadiene 1 were treated with 2.2 equivalents of... 

Mechanistic investigation revealed that two diazo compotmds reacted with one di-lithio reagent affording the intermediate 48 (Scheme 27), which was isolated and characterized by NMR spectrum. Quenching intermediate 48 with H2O under N2 afforded the product 49.49 could be oxidized to afford the 1-imino-pyrrole 46b and the diazo compound 50 [73]. Furthermore, an tmprecedented Zn-complex 51 was obtained via transmetalation of the intermediate 48 with ZnCl2. In this Zn-complex, coordination mode in the solid state was observed. 

Scheme 26 Synthesis of 1-imino-pyrrole derivatives and bis(diazo) compounds via the reaction with diazo compounds...

Iminophosphoranes, mercuration, 2, 432 (Iminophosphoranyl)ferrocenes, synthesis, 6, 202 Imino-pyrrolate systems, with zirconium, 4, 1138-1139 Imino-pyrrolides, with Zr(IV) and Hf(IV), 4, 780 Imino-pyrrolyl ligands, in chromium complexes, 5, 355 Iminosilanes, reactions, 3, 440 Imprinted complexes, on oxide surface, 12, 810 Impurities, glovebox techniques, 1, 215 Inclusion chemistry... 

The amino-pyrrolate complex 99 is another case of a complex with coordination 4 and two coordinating N atoms. In the temperature range 0-50 °C, the 99/MAO catalyst oligomerizes ethylene (/t/w < 8000, Mw//l/n < 2.8) with high activity (< 8x 102gpK(mmol M)-Ih bar ), whereas the monoligated imino-pyrrolate complex 100 shows moderate polymerization activity (19g (mmol M)-1 h 1 bar-1).1086... 

MAO-activated imino-pyrrolate Zr complexes such as 167 also polymerize ethylene, although the activity is moderate (20 gPp (mmol M)-1 h-1 bar-1). Average molecular mass is Mw = 94 000 and the very broad polydispersity (Mv/Mn = 28.4) suggests multiple active species. Interestingly, the X-ray structure of this complex is GTsymmetric and reveals one benzylic group trans to a pyrrolate N atom, while the other benzylic group is trans to an imine N atom.1086,1214 The related MAO-activated mono-imino-pyrrolate pre-catalyst 168 also exhibits moderate ethylene polymerization activity.1214... 

Figure 64 Ethylene polymerization with bis(imino-pyrrolate) Ti-based catalysts.

Zhan M, Zhang S, Zhang WX, Xi Z (2013) Diazo compounds as electrophiles to react with l,4-dilithio-l,3-dienes efficient synthesis of l-imino-pyrrole derivatives. Org Lett 15 4182-4185... 

Prepared by heating ammonium mucate, or from butyne-l,4-diol and ammonia in the presence of an alumina catalyst. The pyrrole molecule is aromatic in character. It is not basic and the imino-hydrogen atom can be replaced by potassium. Many pyrrole derivatives occur naturally, e.g. proline, indican, haem and chlorophyll. 

These observations can be extrapolated to the pyrrole series the 2-amino derivatives are very unstable whereas 3-aminopyrroles appear to be more stable. 3-Amino-l-tritylpyr-role (162) appears to exist in solution exclusively in the imino-A -pyrroline form (163) (83JCS(P1)93). 2-Aminoindole (164) is unusual in that it exists mainly as the 3//-tautomer (165). 4-Alkylaminoindoles (166) undergo an unexpected rearrangement to 4-amino-1-alkylindoles (167) when heated with p-toluenesulfonic acid hydrate (82CC1356). 

Reaction between [W(RC=C)Cl(CO)2(py)2] (R = Ph, Me) with the anionic chelating Schiff base pyrrole-2-carboxaldehyde methylimine yields the cationic complexes [NEt4][W(RCCO)(NN)2(CO)] (where NN is the dianion of the pyrrole ligand). These complexes react with methyltriflate, forming the neutral acetylenic complexes [W(NN)2(CO)(RC=COMe)] (87OM1503). One of the pyrrolic Schiff bases is coordinated via the pyrrole and imino nitrogen atoms, and another one only via the imino nitrogen atom. 

The amino form is usually much more favored in the equilibrium between amino and imino forms than is the hydroxy form in the corresponding keto-enol equilibrium. Grab and XJtzinger suggest that in the case of a-amino- and a-hydroxy-pyrroles, structure 89 increases the mesomeric stabilization and thus offsets the loss of pyrrole resonance energy, but the increase due to structure 90 is not sufficient to offset this loss. Similar reasoning may apply to furans and... 

Even in Ugi reactions of chiral 4,5-dihydro-3//-pyrrole derivatives with aryloxy substituents vicinal to the cWo-cyclic imino group, a low stereoselectivity was found with either chiral or achiral isocyanides and benzoic acid leading to substituted 2-aminoearbonyl-3-aryl-oxy-1 -benzoylpyrrolid ine derivatives82. 

Hoesch reaction. In most cases, a Lewis acid is necessary zinc chloride is the most common. The reaction is generally useful only with phenols, phenolic ethers, and some reactive heterocyclic compounds (e.g., pyrrole), but it can be extended to aromatic amines by the use of BCls. Acylation in the case of amines is regioselectively ortho. Monohydric phenols, however, generally do not give ketones " but are attacked at the oxygen to produce imino esters. Many nitriles... 

The reaction of 5(4H)-oxazolones (32) and miinchnones with triphenylvinylphos-phonium bromide (33) provides a mild synthesis of substituted pyrroles (34) (Scheme 11). The cycloaddition-elimination reactions of 5-imino-l,2,4-thiadiazolidin-3-ones with enamines and ester enolates produce 2-iminothiazolidines. " Chiral isomtinchnone dipoles show jr-facial diastereoselectivity with IV-phenyl- or A -methyl-maleimide in refluxing benzene. ... 

In another approach, 2-(alkylamino)alcohol is employed as starting material for aziridine syntheses with the aid of dihalogenophosphoranes (70BCJ1185). Intramolecular transformation of 3-azidopropyloxirane 73 results in a simultaneous formation of a condensed aziridino[l,2-a]pyrrol-idine system (Scheme 39). The azide group is first transformed into imino-phosphorane 74, the nucleophilic N atom cleaves the oxirane to form betaine 75 [as in the Mitsunobu reaction (81S1)], and the phosphorus is shifted from N to O and then eliminated as phosphane oxide under simultaneous cyclization to bicyclic 76 (89JA7500). 

The imino carbene complexes of tungsten and chromium (e.g., 81) also serve as nitrile ylide synthons (40). The mngsten complexes gave higher yields of the adducts and were strongly regioselective for product 82. For example, for 81 (M=W R = Me, Ph R = Pr, Ph R" = H), the pyrrole 82 was produced in yields of 65-75% with <1% of 83. This route to pyrroles thus has clear advantages over... 

An unprecedented nitrogen elimination reaction of 4-amino-7-benzylpyrrolo [23- f][133]triazine-5-caibonitrile (72) to give the pyrrole derivative 74 has been described. The following mechanism, presumably via a a retro Diels-Alder reaction of the imino tautomer 73, has been proposed <990L537>. 

Irradiation of the pyridinium dicyanomethylide (324) in benzene gives the substituted pyrrole (325), by the postulated route shown (Scheme 242) which originates from the singlet excited ylide. 7,7-Dicyanoazanorcaradiene presumably arises by N—C bond fission in the triplet which produces a dicyanocarbene (of dubious multiplicity) which is trapped by the solvent benzene (67CR(C)(264)1307). Photolysis of the imino-ylide (326) in benzene (equation 200) follows the same pathways initially but the two products result from ring expansions,... 

N6Li4Te2C24H54, Tellurite, bis dilithium[tris-(tert-butylimido)-], 34 46 N7ASC35H22, 2-(5-Amino-3,4-dicyano-277-pyrrol-2-ylidene)-1,1,2-tricyanoethanide, tetraphenylarsonium salt, 34 69 N7C11H3, 5-Amino-3-imino-1,2,6,7-tetracyano-377-pyrrolizine, 34 72... 

The formation of pyrroles or dihydropyridazines appears to be dependent on the E or Z geometry of the a-imino ketone. 

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