A new synthesis of biologically active pyrroles: Formal synthesis of pentabromopseudilin,bimetopyrol, and several antitubercular agents

Although pyrroles have been synthesized from azido dienes, the corresponding reactions of structurally similar nitrodienes had not been investigated until it became the main focus of this study. This article describes the synthesis of several biologically active pyrroles and mechanistically intriguing results in connection with our new approach using nitrodienes in the presence of Ph₃P and a Mo catalyst, bis (acetylaceto)dioxomolybdenum (VI). The final precursor of pentabromopseudilin (PBP), pseudilin, was synthesized in four steps from o-hydroxycinnamaldehyde. An alternate pathway to PBP proceeded through o-methylpseudilin, prepared in two steps from o-methoxycinnamaldehyde. Both starting materials are commercially available. Similarly, bimetopyrol (2-methyl-4,5-bis(p-methoxyphenyl)pyrrole), a potent anti-inflammatory, was prepared using the new methodology. The remarkable conversion of nitrodienes 14 and 15 to bimetopyrol highlights the formation of a nitroso or nitrene intermediate. We also established that 14 and 15 interconvert in the presence of ambient light and each converts to bimetopyrol when reacted separately. The wide application of our synthetic methodology includes preparation of several antitubercular and Herpes Simplex 2 (HSV2) agents.     

Pyrrolidine-thioxotetrahydropyrimidinone as an efficient organocatalyst for the enantioselective Michael addition of cyclic ketones to nitrodienes

Among the various Michael additions, the enantioselective reaction between cyclic ketones and nitrodienes has received little attention in comparison to the corresponding reaction with nitroolefins. A bifunctional organocatalyst consisting of the pyrrolidine moiety and a thioxotetrahydropyrimidinone ring successfully catalyzed this asymmetric transformation. The products of the reaction between various ketones and nitrodienes were obtained in high yields (up to 96%) with excellent diastereo- (up to >98:2 dr) and enantioselectivities (up to 99:1% er).     

Synthesis of 2-mercaptoimidazoles and pyrroles of the adamantane series

2-Mercaptoimidazole derivatives were prepared by the reaction of N-R-(adamantanoyl-l-methyl)amines with potassium thiocyanate. An attempt to synthesize pyrroles from the same amines with the Knorr reaction did not produce the anticipated results.Samara State Technical University, Samara 443010. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 621–623, May, 1994. Original article submitted February 4, 1994.     

A straightforward one-pot multicomponent synthesis of polysubstituted pyrroles

Polysubstituted pyrroles were efficiently synthesized in moderate yields by a one-pot multicomponent reaction starting from primary amines, ethyl glyoxalate and 2-bromoacetophenones in the presence of pyridine in refluxing acetonitrile. This methodology was utilized to synthesize a highly substituted benz[g]indole.     

A three-component one-pot synthesis of penta-substituted pyrroles via ring opening of α-nitroepoxides

A novel and facile one-pot reaction has been developed to synthesize a variety of penta-substituted pyrroles from α-nitroepoxides, primary amines and dialkyl acetylenedicarboxylates under the conditions without catalyst. Furthermore, the controlled experiments has been performed and a possible mechanism has also been proposed.     

New regiocontrolled synthesis of functionalized pyrroles from 2-azetidinone-tethered allenols

A new one-pot approach to synthesize densely substituted racemic and enantiopure pyrroles from beta-lactams has been developed. The approach relies on the regiocontrolled cyclization of beta-allenamine intermediates derived from the ring opening of 2-azetidinone-tethered allenols. In this approach four points of diversity are introduced, one of which is the position of the allene moiety on the beta-lactam ring.     

Thiazolium-catalyzed additions of acylsilanes: a general strategy for acyl anion addition reactions

A strategy utilizing N-heterocyclic carbenes (NHCs) derived from thiazolium salts has been developed for the generation of carbonyl anions from acylsilanes. Synthetically useful 1,4-diketones and N-phosphinoyl-alpha-aminoketones have been prepared in good to excellent yields via NHC-catalyzed additions of acylsilanes to the corresponding alpha,beta-unsaturated systems and N-phosphinoylimines. These organocatalytic reactions are air- and water-tolerant methods to execute robust carbonyl anion addition reactions. Additionally, polysubstituted aromatic furans and pyrroles have been efficiently synthesized in a one-pot process using this carbonyl anion methodology. The addition of alcohols to the reaction renders the process catalytic in thiazolium salt. In an effort to synthesize a potential intermediate along the proposed reaction pathway, silylated thiazolium carbinols have been identified to provide good yields of carbonyl anion addition products when subjected to the standard reaction conditions in the presence of suitable electrophiles.     

Reactions of heterocumulenes with organometallic reagents: XVII. One-pot synthesis of alkoxy and (alkylsulfanyl)-substituted pyrroles and 2,3-dihydropyridines from aliphatic isothiocyanates and lithiated alkoxyallenes

A fundamentally new approach was developed to designing pyrrole and dihydropyridine rings from available allenes and isothiocyanates involving a single preparative stage. Applying the reaction of lithiated alkoxyallenes with aliphatic isothiocyanates we have synthesized previously unknown 1-alkyl(cycloalkyl) pyrroles and 2,3-dihydropyridines with rare alkoxy- and alkylsulfanyl substituents. It was proved that the five- and six-membered azaheterocycles formed as a result of competing reactions of direct intramolecular cyclization of S-alkylated adducts of lithiated alkoxyallenes with isothiocyanates (1-aza-1,3,4-trienes) into pyrroles and of [1,5]-sigmatropic rearrangement into conjugated 2-aza-1,3,5-trienes with subsequent closure into dihydropyridine ring (through 6π-electrocyclization).     

Synthesis of Some Novel S- and N,S-Substituted Chlorobutadienes

Abstract

Mono(thio)substituted nitrodienes were synthesized by reactions of 2-nitro-pentachloro-1,3-butadiene with some thiols [(tert-butylbenzyl)thio- and 2,3,5,6-tetra-fluorophenylthio-] either directly or in ethanol in the presence of sodium hydroxide. N,S-Substituted 1,3-butadienes were obtained from the reaction of the mono(thio)substituted nitrodienes with morpholine and some piperazine derivatives in dichloromethane. Also mono- and di(thio)substituted perchlorobutadienes were synthesized from the reactions of hexachloro-1,3-butadiene with o-aminothiophenol in ethanol in the presence of sodium hydroxide. The structures of the new compounds were characterized by microanalysis and spectroscopic data.     

Rh-catalyzed transannulation of N-tosyl-1,2,3-triazoles with terminal alkynes

The first transannulation of 1,2,3-triazoles with terminal alkynes into pyrroles is reported. The reaction proceeds in the presence of a Rh(2)(oct)(4)/AgOCOCF(3) binary catalyst system providing a straightforward approach to 1,2,4-trisubstituted pyrroles in good to excellent yields.     

Michael Reactions of α-Unsubstituted Trisubstituted 1H-Pyrroles

To obtain stable derivatives of α-unsubstituted pyrroles, the reaction of the test pyrrole 9 with a series of chalcones 14a – h were studied. Michael adducts 16b – h could be isolated. In order to synthesize coloured derivatives, the reaction of different pyrroles 9, 21, 23 , and 25 with diphenylpropynone 19 was investigated. In these cases, too, Michael-addition products were formed. The intense absorption band around 400 nm makes the identification of these derivatives easy.     

Metal free coupling of heteroaryl N-tosylhydrazones and thiols: Efficient synthesis of sulfides

A metal free coupling of heteroaromatic N-tosylhydrazones with thiols is presented. A convenient synthetic route to synthesize heteroaryl N-tosylhydrazones is also showed. Valuable thioethers with pyrroles, pyridines, thieno[2,3-b]pyridines, imidazo[1,2-a]pyridines, and 6H-thieno[2,3-b]pyrroles derivatives were synthesized in good yields. This coupling reaction can be carried out in a one-pot fashion and scaled up to the gram scale by using heteroaryl aldehydes, without the need to isolate the N-tosylhydrazone.     

Oligosubstituted Pyrroles Directly from Substituted Methyl Isocyanides and Acetylenes

The formal cycloaddition of α‐metallated methyl isocyanides 1 onto the triple bond of electron‐deficient acetylenes 2 represents a direct and convenient approach to oligosubstituted pyrroles 3 . The scope and limitations of this reaction (24 examples, 25–97 % yield) are reported along with an optimization of the reaction conditions and a rationalization of the mechanism. In addition, a related newly developed Cu^I‐mediated synthesis of 2,3‐disubstituted pyrroles by the reaction of copper acetylides derived from unactivated terminal alkynes with substituted methyl isocyanides is described (11 examples, 5–88 %yield).     

Highly N2‐Selective Coupling of 1,2,3‐Triazoles with Indole and Pyrrole

Hydrogen‐bond mediated coupling of 1,2,3‐triazoles to indoles and pyrroles results in N2 selective functionalization of the triazole moiety in moderate to excellent yields. The reaction was tolerant of un‐, mono‐ and disubstituted triazoles and was applied to synthesize tryptophan derived fluorescent amino acids.     

Synthesis of functionalized pyrroles via catalyst- and solvent-free sequential three-component enamine-azoene annulation

A new and efficient synthesis of polysubstituted pyrroles by a sequential one-pot three-component reaction between primary aliphatic amines, active methylene compounds, and 1,2-diaza-1,3-dienes (DDs) is reported. The reactions were performed without catalyst and under solvent-free conditions with complete control of pathway selectivity. Notably, the ready availability of the starting materials and the high level of practicability of the reaction and work up make this approach an attractive complementary method for access to unknown polysubstituted pyrroles.     

The synthesis and spectral characterization of novel nitrodiene compounds from thiols

Novel S-, S,S- and S,O-substituted nitrodiene compounds were synthesized from the reactions of 2-nitro-pentachloro-1,3-butadiene (1) and various thiols in different solvent media. The N,S-substituted nitrodienes also were achieved by the reactions of S-substituted nitrodienes with using morpholine, piperidine and piperazine derivatives. All of the new compounds were characterized by elemental analysis, UV-VIS, FT-IR, ¹H-NMR, NMR and mass spectroscopy.     

Solvent-free synthesis of penta-substituted pyrroles: one-pot reaction of amine, alkyl acetoacetate, and fumaryl chloride

A novel, convenient, and efficient approach to the synthesis of penta-substituted pyrroles has been reported based on the multicomponent reaction. Solvent-free condition for the formation of enaminones from primary amines and alkyl acetoacetates and it's reaction with fumaryl chloride lead to the formation of pyrroles that have halide, CH₂CO₂H, ester functional groups, and two alkyl substitutions.     

Tandem Synthesis of Tetrasubstituted NH Pyrroles from Simple Nitriles

An efficient tandem route to obtain tetrasubstituted NH pyrroles in a one-pot manner has been developed, staring from simple nitriles, ethyl bromoacetates, and zinc. This reaction involves oxidative dimerization of the zinc bromide complex of β-enaminoesters using cerium ammonium nitrate (CAN) as an oxidant, affording 2,3,4,5-tetrasubstituted pyrroles in yields up to 91%.     

Gold-catalysed rearrangement of O-vinyl oximes for the synthesis of highly substituted pyrroles

O-Vinyl oximes were synthesised from the reaction of oximes with activated alkynes and subsequently rearranged using gold catalysis to afford highly substituted pyrroles in an efficient and regiocontrolled process. Additionally, pyrroles were formed directly from oximes and activated alkynes in a multifaceted catalysis process.     

N-Heterocyclic Carbene Catalyzed Homoenolate-Addition Reaction of Enals and Nitroalkenes: Asymmetric Synthesis of 5-Carbon-Synthon δ-Nitroesters

Synthesizing synthons: The highly enantioselective title reaction is described. It employs catalytic amounts of N-heterocyclic carbene precursors and transforms a broad range of nitroalkenes, such as nitrodienes, nitroenynes, and nitrostyrenes, through reaction with a broad range of enals, into δ-nitroesters via homoenolate intermediates.