1//-Pyrroles condensation with

There are a few examples of the formation of indolizines from pyrroles. Thus pyrrole condenses with acetonylacetone in the presence of zinc acetate to give 5,8-dimethylindolizine (74) as the major product.87,88 3,4-Diethylpyrrole similarly gives 75.89 This same compound undergoes self-condensation in the presence of zinc acetate to give 76 in 24% yield.89 In another example tetramethine compounds (77) obtained from... 

In principle, the synthesis can be realized as a one-pot process treatment of ketones with hydroxylamine in KOH-DMSO following interaction of the formed ketoximes with acetylene. Various pyrroles with alkyl, cycloalkyl, aryl and hetaryl substituents, as well as pyrroles condensed with aliphatic macrocycles, terpenic and steroid structures, together with their vinyl derivatives now become available. 

Displacement of an ethoxy attached to a vinylic side-chain occurs in mineral acid at ambient temperature with concurrent formation of a C—C bond [2042]. Ethereal hydrogen chloride annulates nitro and side-chain epoxide groups intramolecular reduction-oxidation leads to the 4-quinolinone in high yields [2314]. A C—N bond is formed when a methylthiovinylpyrrole is treated with a strong base and a malonic ester. Lactim ethers such as 5-methoxy-2 -pyrrole condense with acetonedicarboxylate in a base-induced cyclization at room temperature [3258]. 

The most unexpected by-product of the reaction in this case is 2,3,6-triphenylpyridine. Probably, benzyl phenyl ketone (the usual product of partial deoximation of oximes in the conditions for synthesis of pyrroles) condenses with acetaldehyde (product of acetylene hydration in superbase media [105], Equation 1, Scheme 1.166) to form an equilibrium mixture of ethylenic ketones I and J (Equation 2). The ketone J reacts with benzylamine to close 2,3,6-triphenyltetrahydropyridine cycle K. The latter aromatizes to the pyridine (Equation 3). 

Some studies have been carried out on the specificity of the condensation reaction using synthetic monopyrroles. In addition to 2,4-dimethylpyrrole, other pyrroles, such as 2,4-dimethyl-3-ethylpyrrole (kryptopyrrole) and 2-methyl-pyrrole, condensed with MBC in growing cultures or in resting cell suspensions of 9-3-3 (Williams, 1965 Williams and Goldschmidt, unpublished). No pigment was formed if the monopyrrole was 2,5-dimethylpyrrole, 2,4-dimethyl-3-acetyl-pyrrole or unsubstituted pyrrole. 

CH3COCH2CH1COCH3. Colourless liquid which becomes yellow on standing b.p. I9PC. Obtained by boiling 2,5-dimethylfuran with dilute sulphuric acid. It readily condenses with a variety of substances to give derivatives of furan, thiophen and pyrrole, and is a solvent for cellulose acetate. 

Because the a-aminoketone is subject to self-condensation, the condensation with a P-dicarbonyl derivative (6) is usually carried out by generating the a-aminoketone in situ through reduction of an oximino derivative (7) 2iac ia glacial acetic acid is used as the reductant. For example, Knorr s pyrrole... 

Aldehydes and Ketones. Pyrrole aldehydes and ketones are somewhat less reactive than the corresponding benzenoid derivatives. The aldehydes do not undergo Cannizzaro or Perkin reactions but condense with a variety of compounds that contain active methylene groups. They also react with pyrroles under acidic conditions to form dipyrryhnethenes (26). The aldehydes can be reduced to the methyl or carbinol stmctures. The ketones undergo normal carbonyl reactions. 

The unsaturated tetraoxaquaterene (accompanied by linear condensation products) was first synthesized in 18.5% yield by the acid-catalyzed condensation of furan with acetone in the absence of added lithium salts. Other ketones also condensed with furan to give analogous products in 6-12% yield.A corresponding macrocycle was also prepared in 9% yield from pyrrole and cyclohexanone. The macrocyclic ether products have also been obtained by condensation of short linear condensation products having 2, 3, or 4 furan rings with a carbonyl compound. ... 

Dimethoxytetrahydrofuran forms pyrrole derivatives with primary amines, these derivatives then condense with 4-dimethylaminobenzaldehyde in acid milieu to yield colored products [1] ... 

Dimethylaminocinnamaldehyde reacts with primary amines to form colored or fluorescent Schiff s bases (I). Pyrroles react with the reagent to form colored or fluorescent condensation products (II) ... 

The mechanism of the original Knorr pyrrole synthesis entails in situ reduction of the oxime moiety to an amine, condensation with the second carbonyl compound, and cyclization with loss of a second molecule of water to give a pyrrole for example, 10 + 11 to 12. Several studies have demonstrated that different pathways and pyrrole products obtain depending on the substrates. 

Allen et al mainly on the evaluation of data reported by previous workers, advanced structure (5) for 2-methylpyrrole dimer. These data were (a) the monobasic nature of the dimer and (b) the conversion by aqueous acid into an indole which they showed by elimination (i.e., by the synthesis of 2,5-, 2,6-, and 2,7-dimethylindoIes) to be 2,4-dimethyIindole (this compound has since been synthesized by Marion and Oldfield ). Structure (5) for the dimer was confirmed by Edwards and Smith by conversion, by way of the methiodide (6), into the pyrrolidinopyrrole (7), the structure of which was proved by synthesis l,5-dimethylpyrrolid-2-one was condensed with 2-methyI-pyrrole by means of POCI3 to give the cation (8), isomeric with the... 

The condensation of 2,5-diunsubstituted pyrroles with formic acid20 is a viable method to produce porphyrins. However, the most common procedure21 22 involves the heating of the corresponding pyrroles 1 with aldehydes and aldehyde derivatives like imines or a Mannich reagent in the presence of acid. The reaction is initiated by electrophilic attack of the aldehyde (or aldehyde derivative) to the pyrrole 1. The formed (hydroxyalkyl)pyrrole 3 then undergoes electrophilic substitution with another pyrrole to form a dipyrrylmethane 4. Repeated addition of aldehyde and pyrrole finally forms a tetrameric (hydroxyalkyl)bilane 5. 

In a similar manner, aminotriazole 260 has been condensed with 1 -mcthyM-m ethyl sulfanyl-2,5-dioxo-2,5-dihydro-17/-pyrrole-3-carbonitrile 262 to give rise to analogous product 263 (Equation 72) <1996H(43)1597>. 

Nitrobenzofurazan 240 and 4-chloro-7-nitrobenzofurazan 232 also condense with isocyanoacetates in the presence of the non-nucleophilic base l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to give tricyclic pyrrole derivatives 241 in excellent yields (Scheme 60) <2005T11615>. 

Katritzky offers a general one-pot alternative approach to polysubstituted pyrroles utilizing disubstituted olefins of which a wider variety is commercially available compared to acetylenes . Thus, thioamides 32 were subjected to Mannich condensation with aldehydes and BtH to yield functionalized thioamides 33 which were then treated with base... 

The amino pyrrole 29 derived from the reaction with phenylhydrazine <1998JOC9131> was found to undergo an acid-catalyzed intramolecular condensation with the carbonyl present to give the 3//-pyrrolo[l,2-A pyrazole 30 ring system in a good yield (75%) (Equation 2). 

In order to prepare asymmetric meso-porphyrinylsugar derivatives (mono-, di- and tri-glycosylarylporphyrins), pyrrole was condensed with a mixture of glycosylated and nonglycosylated aldehydes.17,21,24,44 46 Several porphyrinylsugar derivatives were prepared by this synthetic methodology. The saccharide unit can be directly linked to the porphyrin macrocycle 35-50 or separated from the phenyl group by a spacer, such as in the case of derivative 51-53 shown below (Fig. 4). 

In chlorophyll iron as complex-forming metal is replaced by magnesium (Willstatter). The structure of chlorophyll differs from that of haemin as follows. In chlorophyll one propionic acid chain (a) in oxidised form has condensed with a methine carbon atom to form a cyclopentane ring which takes the position at (c) of the vinyl ethyl. Further the two carbonyl groups are esterified and one of the four pyrrole rings is partially hydrogenated... 

Unsubstituted acetone resists condensation with 2,3-diformylthiophene (71BSF1437) but, surprisingly, reacts with 3,4-diformylfuran, -thiophene, and -pyrrole or 1,2-diformylferrocene (Table II). The reactivity of hydroxy-acetone allows the preparation of heterocycle-fused tropolones. 

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... 

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