Pyrrol-2-aldehyde

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. 

Redistilled N, O-persilylated L-proline 438 reacts with pivaldehyde in pentane at ambient temperature to give the 0,N-acetal 439 in 78% yield in the presence of LDA this condenses, a to the carbonyl group, with N-alkyl-2-pyrrole aldehydes [48] (Scheme 5.14). 

Boiadjiev and Lightner synthesized fluorescent tricyclic-bridged pyrrinones such as 31 by base-catalyzed condensation-cyclization of pyrrolin-2-one 112 with pyrrole aldehyde 113 (Equation 24) <2005M553, 2005JOC689>. 

The use of Pd/C to effect decarbonylation reactions, which has long been known, is equally successful with pyrrole aldehydes, e.g., 204 to 205 [108]. 

Krausz el al. have synthesised two series of amino acid porphyrinylsugar derivatives (Fig. 5). One of them involves the coupling of adequate glycoporphyrin derivatives, prepared by pyrrole/aldehyde condensation methodology, with 9-fluorenylmethoxycarbonyl-L-alanine (Fmoc-L-alanine) to give the tri-, di-, and mono-alanine glycoporphyrin derivatives 54—57 after the deprotection step the other series (58) involves a glucosylamino acid moiety instead of the alanine in their preparation.21,44... 

The condensation reaction of some selected furo[3,2-b]pyrrole aldehydes (8g, 266,267) with benzothiazolium salts was carried out in refluxing methanol with pyridine as catalyst giving 269a-d <2004MOL241>. 

The action of phosphorus halides on pyrrolinones and related compounds offers an alternative route to chloropyrroles. Yields of around 60% of 2,5-dichloropyrroles were obtained in this way from N-substituted succinimides (82ZC126). Vilsmeier reaction of N-alkylsuccinimidals formed chlorinated pyrrole aldehydes in modest yields (90CJC791), and there are other examples [66YZ158 81H(15)547]. A useful synthesis of chloropyrrole-2-carboxylates employed the action of phosphorus pentachloride on pyrrolidin-2-one-5-carboxylates (40) (87CB45) (Scheme 15), and in a Pummerer-type reaction pyrrol-3-yl sulfoxides were transformed by thionyl chloride into chloropyrroles. Yields were increased to >80% by the use of oxalyl chloride (88JOC2634) (Scheme 15). 

Substituted pyrrole aldehydes, ketones and esters have been studied in a similar fashion to the 2-substituted derivatives. The barrier to rotation about the ring to carbonyl group... 

Pyridines and pyrroles can be formed in different pathways by Mail-lard reaction. The formation of 5-methyl pyrrole aldehyde and 6-methyl-3-pyridinole has been observed by Nyhammar et al (17) by the reaction of isotope labelled 3-deoxyosone with glycine. The 3-deoxy-hexosone represents an -dicarbonyl compound and in this way the Strecker degradation occurs. Another pathway is the reaction of fu-rans with ammonia. Under roast conditions, we have obtained primarily the corresponding pyrrole, whereas we found the corresponding py-... 

Why is pyrrole aldehyde 2.44 less reactive to nucleophiles than, say, benzaldehyde Why is pyrrole alcohol 2.45 readily polymerised on exposure to acid ... 

A variation of this method that removes the water produced in the pyrrole/aldehyde or hydrated aldehyde condensation has been used to produce meso-tetrakis(perfluoroalkyl)porphyrins. Lindsey s laboratory has also reported a rational synthesis of weyo-substituted porphyrins bearing one nitrogen heterocyclic group that can readily be used for preparing other mono-functionalized porphyrins, methods for minimi zing scrambling in the synthesisof tran -porphyrins from dipyrromethanes and aldehydes, and a rational synthesis of porphyrins bearing up to four different meso substituents. ... 

Vinylogous porphyrins are formally built up of odd-numbered carbon spacers separating four pyrrole rings. There are, however, several expanded porphyrins that contain four pyrrolic or pyrrole-like subunits that contain only even-numbered carbon spacers. These macrocycles will be grouped under the general heading stretched porphycenes , since they are typically prepared via the low-valent titanium mediated coupling of pyrrolic aldehydes just as are the porphycenes (cf. Chapter 3). 

The Cram modification has not been greatly exploited in multistep synthetic endeavors, possibly because of the above-mentioned need to preform and isolate the hydrazone intermediate coupled with very slow addition of the hydrazone. This latter requirement is particularly inconvenient when milligram quantities are involved. The aldehyde in a triterpenoid (partial structure 18) was successfully reduced to the corresponding methyl group using the Cram method, albeit in low yield (32%). Notably, the hydrazone (lO mg) was not added slowly. The Cram process was not successful for the reduction of the cyclo-butanone (19) (the Huang-Minlon process succeeded), or the pyrrole aldehydes (20) and (21). ... 

Some of the heterocyclic compounds among the Maillard products, for example, pentosi-dine 370 and pyrraline 371, are AGEs in the skin of diabetic patients as well as in the brain of Alzheimer patients [319,320,321,322,323,324,325,326,327,328,329]. The observation that the aldehyde 372, the Maillard product of 33 and -propylamine, reacts with the amine and 369 to give 373 and 374, respectively, led to the assumption that pyrrole aldehydes might also be precursors of the lysine side chain of proteins [320,330,331,332] (O Scheme 71). 

An acid-resistant protecting principle for carbonyl groups consists of the a,a-dicyanoethylene derivatives (96). They are obtained from carbonyl compounds, e.g. pyrrole aldehydes (95), by Knoevenagel condensation with malodinitrile. In general, mineral acids and Lewis acids, which are used in Friedel-... 

One-pot pyrrole-aldehyde condensations as versatile self-assembly processes 04AG(E)1918. 

Analogous condensations, but with a pyrrole aldehyde lead to mesomeric dipyrromethene cations, which play an important part in porphyrin synthesis. Thus, using formyldipyrromethane as the aldehyde and a second mole as the pyrrole component, with air as oxidant, porphine is formed directly, as its magnesium derivative, possibly via a dipyrromethene cationic intermediate. ... 

These are stable compounds which do not polymerise or autoxidise. For the most part, pyrrole-aldehydes and -ketones are typical aryl-ketones, though less reactive - such ketones can be viewed as vinylogous amides. They can be reduced to alkyl-pyrroles by the Wolff-Kishner method, or by sodium borohydride via elimination from the initial alcoholic product (cf. 16.11). Treatment of acyl-l-phenylsulfonyl-pyrroles with f-butylamine-borane also effects conversion to the corresponding alkyl derivatives. ... 

In fact the pyrrole/aldehyde condensation methodology allows the use of a mixture of aldehydes, providing that the required product can be easily purified from the final statistical product-mixture. Using two aldehydes, that usually happens when their relative proportions are 3 1. 

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