Pyrrole 3-amino- from

The exploration of the chemistry of azirines has led to the discovery of several pyrrole syntheses. From a mechanistic viewpoint the simplest is based upon their ability to behave as a-amino ketone equivalents in reactions analogous to the Knorr pyrrole synthesis cf. Section 3.03.3.2.2), as illustrated in Schemes 91a and 91b for reactions with carbanions. Parallel reactions with enamines or a-keto phosphorus ylides can be effected with electron-deficient 2//-azirines (Scheme 91c). Conversely, electron-rich azirines react with electron deficient alkynes (Scheme 91d). 

A more complex reaction is involved in the cooligomerization of acetylenes and tert-butyl isocyanide using nickel acetate as the catalyst (Scheme 20)43 the nature of intermediate complexes leading to the formation of 2-cyano-5-terf-butylaminopyrroles has not been established. Cocyclization of tert-butyl isocyanide with coordinated hexafluoro-2-butyne gives rise to coordinated cyclopentadienone anils for molybdenum systems,44 hence the nature of acetylene substitutents and of the organometallic catalyst play crucial roles in these processes. The pyrrole products from the former reaction can be decomposed by sulfuric acid and the overall sequence provides a simple synthesis of 5-amino-2-cyanopyrroles (Scheme 20). 

To make tryptophan analogs, Gronowitz and coworkers conducted a pyrrole annulation from an aminoiodopyrimidine utilizing the Larock indole synthesis conditions (see Section 1.10.) [80]. They prepared heterocondensed pyrrole 115 by treating 4-amino-5-iodopyrimidine 114 with trimethylsilyl propargyl alcohol under the influence of a palladium catalyst The regiochemical outcome was governed by steric effects. 

Ilac Knorr pyrrole synthesis from a-amino ketones and /3-dicarbonyl compounds 3.06.3.4.1... 

A one-pot synthesis of pyrroles (90) from 1,2,5-selenadiazoles (88) with 1,3-diketones in the presence of zinc powder and acetic acid was reported. Initial reductive elimination of selenium gave a diamine (89), then one amino group was condensed with a 1,3-diketone followed by intramolecular cyclization to afford a pyrrole (90). [94JCS(P1)2201]... 

Nagafuji, P., Cushman, M. A General Synthesis of Pyrroles and Fused Pyrrole Systems from Ketones and Amino Acids. J. Org. Chem. 1996, 61,4999-5003. 

Pyrrole synthesis from 1,3-dicarbonyl compounds (or enamino Ketones) and a-amino acids via cyclization of enamino acid intermediates. 

Pyrrole Derivatives from 2-Amino-2-deoxy-o-glticose... 

Pyrrole Derivatives from 1-Amino-l-deoxy-D-frudoses... 

Borohydride trapping was also used to demonstrate the presence of an iminium ion in the pathway involved in pyrrole biosynthesis from two molecules of A-amino-levulinic acid [123]. This reaction, shown in Scheme 23, involves iminium ion formation with 1 mole of substrate, eneamine formation by deprotonation, and then... 

Formation of the pyrrole 278 from l-amino-3-alkyn-2-ol 276 is catalyzed by PdCl2. The reaction can be understood as aminopalladation to generate 277, followed by protonolysis and dehydration [116]. Indoles are prepared from o-alkynyl aromatic amines. The required alkynyl amine 279 is prepared from o-iodoacetanilide. Aminopalladation of 279 and protonolysis affords 280 [117]. 

The key intermediates in the formation of furan and pyrrole derivatives from 3-deoxyglycos-2-uloses via P-dicarbonyl compounds are 3-deoxy-2,4-diuloses and l-amino-l,3-dideoxy-2,4-diuloses. Cyclisation, dehydration and keto-enol tautomerisation of diuloses yield 2-acetylpyrrole derivatives as the main products (Figure 4.96). 

In contrast to many studies on cycloaromatization via transition metal-vinylidene complexes as key reactive intermediates, only one example of such a reaction via transition metal-allenylidene complexes has been reported to date. In 2008, Yada et al. reported the formation of substituted fiirans 78 from 3-butyne-l,2-diols 77 in the presence of a catalytic amount of thiolate-bridged diruthenium complex (Scheme 21.33) [45]. This methodology was also applied to the formation of a substituted pyrrole 80 from l-amino-2-butyn-2-ol 79. It is noteworthy that thiolate-bridged diruthenium complexes worked as effective catalysts toward cyclization involving both ruthenium-allenylidene and ruthenium-vinylidene complexes as key reactive intermediates. 

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