2H-Pyrroles

The pyridine-like nitrogen of the 2H-pyrrol-2-yiidene unit tends to withdraw electrons from the conjugated system and deactivates it in reactions with electrophiles. The add-catalyzed condensations described above for pyrroles and dipyrromethanes therefore do not occur with dipyrromethenes. Vilsmeier formylation, for example, is only successful with pyrroles and dipyrromethanes but not with dipyrromethenes. 

ANTIBIOTICS - NUCLEOSIDES AND NUCLEOTIDES] (Vol 3) 5-(2H-Pyrrol-2-ylidenemethyl)-2,2y-bipyrrole [22187-69-5]... 

Reduction of indolenines with sodium and ethanol gives indolines. The pentachloropyr-role, obtained by chlorination of pyrrole with sulfuryl chloride at room temperature in anhydrous ether, was shown by spectroscopic methods to have an a-pyrrolenine (2H-pyrrole) structure (222). It is necessary, however, to postulate that it is in equilibrium with small but finite amounts of the isomeric /3-pyrrolenine form (3//-pyrrole 223), since pentachloropyrrole functions as a 2-aza- rather than as a 1-aza-butadiene in forming a cycloadduct (224) with styrene (80JOC435). Pentachloropyrrole acts as a dienophile in its reaction with cyclopentadiene via its ene moiety (81JOC3036). 

H-Pyrrole, 3,4-dihydro-5-methyl-UV, 4, 179 (65JCS2313) lH-Pyrrole-3-acetic acid, ester C NMR, 4, 172 (74JCS(P2)1004)... 

Scheme 34 Cyclizations of 5-hetera-l-metalla-l,3,5-hexatrienes 157 to mainly yield 2H-pyrroles [37]. For further details see Table 8...

Ethoxypyrrolin-5-one l-Pyrrolin-5-one, 2-ethoxy- (8) 2H-Pyrrol-2-one, 5-ethoxy-3,4-dihydro- (9) (29473-56-1) tert-Butyl N-(l-ethoxycyclopropyl)carbamate Cyclopropanecar-bamic acid, 1-ethoxy-, tert-butyl ester (8) Carbamic acid, (1-ethoxycyclopropyl)-, 1,1-dimethylethyl ester (9) (28750-48-3 41879-49-6)... 

DEPMPO 2-Diethoxyphosphoryl-2-methyl-3,4-dihydro-2H-pyrrole-l-oxide... 

The formation of 2H-pyrroles (21) and a pyrrole derivative (22) from the reaction of 3-phenyl-2//-azirines and acetylenic esters in the presence of molybdenum hexacarbonyl is intriguing mechanistically (Schemes 24, 25).53 Carbon-nitrogen bond cleavage must occur perhaps via a molybdenum complex (cf. 23 in Scheme 26) but intermediate organometallic species have not yet been isolated.53 Despite the relatively poor yields of 2H-pyrrole products, the process is synthetically valuable since the equivalent uncatalyzed photochemical process produces isomeric 2H-pyrroles from a primary reaction of azirine C—C cleavage54 (Scheme 24). 

Efficient oxidation of imines into nitrones can be achieved by using methyl (trilluoromethyl)dioxirane as an oxidant. This method provides enantiopure nitrones derived from 2H -pyrrole 1-oxide (23, 24). 

Phenyl-1-pyrroline 1-Pyrroline, 2-phenyl- (8) 2H-Pyrrole, 3,4-dihydro-5-phenyl-(9) (700-91-4)... 

It is interesting to note that these compounds attract mainly the males of the respective species. Therefore, these compounds might be pheromone mimics. Protein hydrolysates, on the other hand, attract both sexes of most Tephritids and are widely used as food baits. However, volatiles from protein hydrolysates may not be simply food attractants. The cyclic imine, 3,4-dihydro-2H-pyrrole, has been identified in protein hydrolysate volatiles (12), and this compound has been identified by Baker and coworkers (11) as the sex pheromone Which attracts virgin females to the sexually mature male Medflies. Why the protein hydrolysate volatiles attract the males and other species remains unanswered. 

In 2006, Chatani and coworkers published a rhodium vinylidene-mediated alkyne cyclodimerization incorporating allylamine (Table 9.13) [26]. Although RhCl(PPh3)3 alone was a competent catalyst for the stereospecific formation of ( )-3-alkylidene-3,4-dihydro-2H-pyrroles (69), the addition of an ammonium salt helped to suppress undesired alkyne homocoupling. Under optimized conditions, a variety of functionalized alkynes underwent cyclodimerization with allyl- or crotylamine in good yield. 

Tetracyan-ethen cyclisiert mit dem Natrium-Salz von Benzimidazol zu Bemimidazolium- dicyan-[3,4-di-cyan-5-benzimidazolo-2H-pyrrol-2-yUdenammo]-methanid (33%). Mit Lewissauren geht die Kondensation weiter zu penlacyclischen Verbindungen526. 

C35H22ASN7, 2-(5-Amino-3,4-dicyano-2H-pyrrol-2-yhdene)-1,1,2-tricyanoethanide, tetraphenylarsonium salt, 34 69... 

The ring proton chemical shifts of 2H-pyrroles and 3H-pyrroles are as expected for conjugated imines (B-90MI201-02). 

Polyalkylated 2- and 3-pyrrolenines (2H- and 3H-pyrroles) and 3-indolenines (3H-indoles) are formed by methylation of the parent 1H heterocycles (see Section 3.05.1.2.7), but the acid-catalyzed or thermal rearrangement of 2,2,5-trisubstituted 2H-pyrroles and of 3,3-disubstituted 3//-indoles yields the corresponding 2,3,5-trisubstituted IH-pyrroles and the 2,3-disubstituted l//-indoles, respectively (see Section 3.05.1.1). 

As with the alkyl and aryl derivatives of the pyrrolenines and indolenines, a tautomeric equilibrium has also been noted between the pentachloro-2//- and -3H- pyrroles, such that when the 2//-pyrrole, produced by chlorination of 2,3,4,5-tetrachloropyrrole or of 3,4-dichloromaleimide, is allowed to react with dienophiles, the adducts are those formed by cycloaddition with the 3H-pyrrole tautomer (Scheme 84) (80JOC435, 80JA7862, 81JOC3036). Cycloaddition with cyclopentadiene occurs on the 2H-pyrrole, which behaves as the dienophile. 

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