3H-pyrrole

Die Reduktion cyclischer Schiff scher Basen mit Hydriden verlauft ahnlich den acycli-schen Verbindungen zu Aminen. Azirine werden durch Lithiumalanat zu den Aziridi-nen reduziert, mit Natriumboranat in Methanol erfolgt dagegen Solvolyse zum Me-thyl-aminomethyl-ather5. 4,5-Dihydro-3H-pyrrol-Derivate lassen sich mit Lithiumalanat6 und Natriumboranat7 zu Pyrrolidinen reduzieren. Ahnlich konnen auch Pipe-... 

The 5-dig-mode of cyclization has been applied in the synthesis of N-heterocycles. For example, treatment of the /i-allenyl dithiosemicarbazide 37 with Bu3SnH and AIBN in hot benzene furnishes the substituted 3H-pyrrole 38 in 41% yield and the isomeric heterocycle 39 in 30% yield (Scheme 11.13) [68], Iminyl radical 40 is formed via Bu3Sn addition to the thiocarbonyl group of the radical precursor 37 and fragmentation of the adduct (not shown). Nitrogen-centered radical 40 adds 5-dig-selectively to provide substituted allyl radical 41. The latter intermediate is trapped by Bu3SnH to furnish preferentially product 38 with an endocydic double bond. 

Carbonsaure-amid-hydroximid und 99 g (1 mol) 2-Methoxy-4,5-dihydro-3H-pyrrol bzw. 127 g (1 mol) 2-Methoxy-4,5,6,7-tetrahydro-3H-azepin werden unter Riihren erwarmt, vvobei bei 110° entstehendes Methanol iiber eine 30-cm-Vigreux-Kolonne abdestilliert wird. Innerhalb von 2 h steigert man die Temp, auf 200° und destillicrt anschlicfiend den Riickstand i.Vak. 

Die reduktive Aminierung von 2-(3-Oxo-alkyl)-l,3,4-oxadiazolen verliiuft analog unter intra-molekularer Ringtransformation uber 2-(2-Acyl-hydrazino)-5-methyl-4,5-dihydro-3H-pyrrole (33-54%) zu 5-Methyl-6,7-dihydro-5H-[Pg.620]

Hydroximino-2,4,5-lrimethyl-3H-pyrrol liefcrt mit Flydroxylamin 4-(2-Hydroximino-1 -methyl-propyl)-3-me thyl-furazan117 ... 

In diesem Zusammenhang sei auch auf die Reduktion von 5-Carboxy-2-cthyl-4,5-dihydro-3H-pyrrol zu els- bzw. trans-5-Ethyl-prolin hingewiesen1 IJ ... 

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. 

With methyl /-propyl ketoxime (competition of the CH3 and CH groups) only 2-/-propylpyrrole and its vinyl derivative can be isolated in 10 and 15% yield, respectively. Under these conditions (Table XXII), the 3H-pyrrole 78 appears to be unstable (Scheme 39). 

The 2H - and 3H -pyrroles and -indoles are considerably more basic than the corresponding 1//-isomers and they readily undergo alkylation to give the quaternary salts, which are then highly susceptible to nucleophilic attack. Thus, for example, methylation of the trialkyl-3//-indole (507), followed by reaction with aqueous base, yields the indolin-2-ol (508). A similar reaction sequence results from the acylation of (507) under Schotten-Baumann conditions to give (509 X = OH). When the benzoylation is conducted in benzene in the absence of the base, the 2-chloroindoline (509 X = C1) is formed and acylation of (507) with a carboxylic acid anhydride produces the ester (509 X = OCOR) (79HC(25-3)l). 

Note that because of the use of beta bonds, rather than fixed single and double bonds, there is not inconsistency between the molecule depicted and the common vs. the alternate IUPAC names. The double bonds are NOT localized, as the IUPAC picture implies. To the contrary, 5H-Pyrrole is, because of symmetry just another (non-canonical) name for 2H-Pyrrole. Additionally, one should note that a 3H-Pyrrole can also be formed. This would have as its systemic name NP(CP)4 (1H). 

In the reaction of 3,5-dimethyl-2,6-diphenylpiperid-4-one oxime (10) with acetylene and RbOH-DMSO, migration of the 3a-Me group to the anionic nitrogen atom occurred, leading to 5,7-dimethyl-4,6-diphenyl-4,5,6,7-tetrahydropyrrolo[3,2-c]pyridine (11) (04CHE326). The formation of the N-anion caused aromatization of the tetrahydropyridine ring. Tetrahydropyrrolo[l,2-c]pyrimidine 12 resulted from the decomposition of the intermediate 3H-pyrrole in a retro-Mannich reaction (Scheme 3). 

H-Pyrazol 3-(bzw. 4)-Methyl-4,5-dihydro- IV/lb, 110 Pyrimidin 1,4.5,6-Tetrahydro-(Hydrochlorid) IV/lc, 316f. 3H-Pyrrol 2-Amino-4,5-dihydro-IV/ld, 112... 

Oxid), 1412 (NH - N-oxid) 3H-Pyrrol-l-oxid 2-Methyl-4,5-dihydro- E14b, 146 (aus N02-Keton) Pyrrolidin... 

H-Pyrrol 2-Amino-5-methyl-4,5-dihydro- -1-oxid X/4, 349 Pyrrolidin l-Hydroxy-5-imino-2-methyl- X/l, 440... 

Azetidin l-(Cyan-carbonyl)-2,2-dimethyl- El6c, 771 (aus 4,5-H 2 3H-pyrrol-l -oxid) Benziniidazol 2-Hydroxy-4,5,6,7-tetrahydro- E8c, 34 [1,2-(O —SiR3)2 —cyclohexen + (H2N)2CO]... 

H-Pyrrol 5-Ethenyl-2-methyl-4,5-dihydro- -1-oxid E14b, 1432 (aus Oxim intracycl. C,N-Bild.)... 

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