Formyl pyrrole

Conjugated dipyrrolic pigments, the dipyrromethenes, are synthesized by add-catalyzed condensation of an a-formyl pyrrole and an a-unsubstituted pyrrole. They are readily protonated and deprotonated and are difficult to purify by chromatography. 

Viaylpyrroles and 3-vinylpyrroles can be prepared by the base-catalyzed condensation of the corresponding formyl pyrroles with activated... 

Mit Diboran verlauft die Reaktion in THF oder Bis-[2-methoxy-athyl]-ather ahnlich12, 13. Mit dieser Methode konnen auch N-Methyl-Verbindungen hydrogenolytisch umge-setzt werden (2-Formyl-pyrrol polymerisiert13) z.B. ... 

Dimethyl-4-athyl-2-formyl-pyrrol —> 2,3J-Trimethyl-4-athyl-pyrrol13 49% d.Th. 

The protonation of acetyl- and formyl-pyrroles occurs on the carbonyl group (Skylar et al., 1966). So, for example, in the nmr spectrum of 2,4-dimethyl-3-acetyl-pyrrole in concentrated acid the vinyl (C-5) proton resonance is retained, although there is exchange in deuteriated acid (Melent eva et al., 1971). The behaviour of carbethoxy-substituted pyrroles is more complicated, however. While 3-carbethoxy derivatives [168] and the 2-carbethoxy derivatives unsubstituted at the 5-position [169] protonate at the a-position of the ring and are not exceptional, the 2-carbethoxy derivatives with a methyl group at the 5-position [170] give evidence in the nmr... 

The Reimer-Tiemann reaction is not an effective route to formyl-pyrroles or -indoles (see Section 3.05.1.6) and the oxidation of alkyl and hydroxyalkyl derivatives of the heterocycles and the reduction of carboxylic acid derivatives are discussed in Sections 3.05.2.2 and 3.05.2.4, respectively. 

The apparent fickleness of the acyl-pyrroles and -indoles in their reaction with carbanions to form new C—C bonds arises from the contribution made by the zwitterionic structure, e.g. (410b), to the resonance hybrid and the choice of the reaction conditions is critical for a successful nucleophilic reaction. Thus, formyl-pyrroles and -indoles do not normally undergo the Cannizzaro reaction nor do they form stable cyanohydrins or undergo benzoin-type reactions. However, surprisingly, 2-formylpyrrole reacts with arylaldehydes in the presence of potassium cyanide to yield (428), which is easily oxidized to (429) (B-77MI30505). It is noteworthy that the presence of an ester substituent adjacent to the formyl group modifies the mesomeric interaction to such an extent to allow the formation of (430) in low yield, as a result of an initial benzoin-type self-condensation (Scheme 76) (68BSF637). 

Although less reactive than many aromatic aldehydes, formyl-pyrroles and -indoles undergo base-catalyzed reactions with a variety of activated methylene compounds to yield compounds of the type (431) and (432), where, for example, X, Y = C02Et, C02Et COMe,... 

Condensation of formyl-pyrroles and -indoles with a wide range of other activated methylene compounds has been reported. These include, for example, hydantoin, which provides a useful synthetic route to tryptophane and j8- (pyrrolyl)alanines, thiohydantoin, rhodanine and AT-substituted barbituric acids (B-77MI30505, 79HC(25-3)357). Flash pyrolysis of the condensation product derived from 3-formyl-2,5-dimethylpyrrole with Meldrum s acid produces 6-hydroxy-2-methylindole, (440) — (441) (74AJC2605), whilst the analogous... 

A direct synthesis of 3H-pyrrolizin-3-one derivatives has been effected. Reaction of 2-benzoylpyrrole with ylides 148 gave the 3H-pyrrolizin-3-one 149 9 ,92 analogous reaction of 2-formyl pyrroles could be achieved with... 

JOC4394, 1995CEJ68, 1997JCS(CC)1689). Smith and coworker (1997JOC5133) have also reported the formation of sapphyrin from biladi-ene 109 and formyl pyrrole. 

As a consequence of bottle aging, carbohydrate conversions can occur, although slowly at cellar temperature, to form the caramel-like 2-furfural aroma for example, in aged Madeira wines. Rapp and Giintert (86MI141) have shown that such carbohydrate decomposition in Riesling wines leads to 2-furfural 9,2-acetylfuran 10, ethyl furan-2-carboxylate 11, 2-formyl pyrrole 12, and 5-hydroxymethylfurfural 13. 

Aus l-(2-Pyrrolyl-methyliden)-pyrrolidiniumperchlorat erhalt man das sonst schwer zugangliche 2,4-Di-formyl-pyrrol (437o)68 ... 

Diese Arbeitstechnik ist bei den eindeutigen Donorhetarenen (z. B. Pyrrol) nicht anwend-bar, da die Formyl-pyrrole unter den Rcaktionsbedingungen entweder mit sich selbst oder mit den jeweiligen Edukten unter elektrophiler Substitution reagieren. 

Pyrrol selbst liefert nur in geringer Ausbeute 2-Formyl-pyrrol, 1-Methyl-pyrrol reagiert unter diesen Bedingungen nicht mehr. 

Tab. 12 Formyl-pyrrole aus Pyrrole namitChlormethylen-dimethyl-iminium-chlorid(A) bzw. DMF/Benzoylchlorid (B)... 

Auf diese Weise ist femer 3,5-Dimethyl-4-ethoxycarbonyl-2-formyl-pyrrol zuganglich659. 

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