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Microwave-assisted Palladium-catalyzed cyclization of allenyl indoles
No full textAs a part of our study directed to the development of intramolecular palladium-catalyzed procedure in obtaining polyheterocyclic systems, and to study the reactivity of indole derivatives, the present work is regarding the reactivity of N-allenyl 2-indolecarboxamides. Heteroannulation processes involving an allenyl functional group have been extensively studied in the past years, in particular allenamides represent a versatile and effective class of building blocks for generating nitrogen-containing heterocycles. The interest of our substrates is due to the presence of the allenyl group tethered to the indole nucleus which nitrogen atom should be suitable nucleophile to give intramolecular cyclization. The pathway proceeds with the involvement of a -allylpalladium intermediate, generated by carbopalladation of the allene moiety. The complex plays a fundamental role in terms of regio- and stereoselectivity. The subsequent step occurs following divergent outcome but in both cases the carbon in the position of the 1,2-diene is involved. The reaction is totally regioselective giving only the exo-cyclized product.
The key step, in the presence of an aryl iodide, consists of a carboamination process, to give imidazo[1,5-a]indole derivatives. The second strategy, without the intervention of the aryl iodide, consists of a new hydroamination reaction that proceeds exclusively under microwave irradiation.
The alternative hypothetical product arising from the involvement of indole C-3 nucleophile to the -allyl complex is never observed
New environmental friendly N-aryl indolines synthesis through C-N bond formation
No full textThe indoline skeleton is an ubiquitous scaffold found in a range of biologically active alkaloid and pharmaceutically active compounds. Indolines have also been successfully employed as chiral auxiliaries in asymmetric synthesis.1-2 On the other hand indolines are also useful for various application ranging from dyes, dye sensitized solar cell, to fuel cell (H2 storage).3 Our research group is always interested in heterocyclic systems synthesis and to this goal Pd-catalyzed reactions have been extensively studied.4
Among the known Pd-catalyzed reactions typologies Heck reaction, Buchwald-Hartwig reaction, oxidative coupling, arylation have been reported previously by our research group. In particular the amination reaction are nowadays one of the most powerful tool to obtain C-N bond formation.5-8 The evolution of this reaction was toward the use of weak bases in order to leave intact other functional groups. The further evolution was addressed to improve yield and applicability, and this goal was achieved using different ligands and through their optimization. Today we try to further enlarge the applicability and to use environmental friendly procedures. Last but not least we try to develop economic and scalable synthesis to switch the use of this reactions from research to industry. We present here a new kind of solvent “QUASI-free” reaction, combined with the use of a commercially available ligand and the use of a weak and cheap base, K2CO3. Irradiation by microwaves is the other key feature of this protocol
SINTESI DI BENZODIAZEPINE TETRACICLICHE TRAMITE AMMINAZIONI CATALIZZATE DA PALLADIO/CICLOADDIZIONI 1-3 DIPOLARI
No full textPalladium-catalyzed intramolecular reactions of indolyl allenamides
No full textThe allene derivatives and allenamides in particular represent a versatile class of building blocks for generating nitrogen-containing heterocycles.1 The present work is regarding the behavior of allenamides derived from indole-2-carboxylic acid. The cyclization reactions occurred following different pathways but in all cases involving the carbon in the -position of the 1,2-diene. The carbopalladation of the allene moiety, through the formation of a -allylpalladium intermediate, resulted in the carboamination process in the presence of aryl iodides. By using a substituted o-arylhalide allenamide as substrate a double intramolecular version of the process was observed with the formation of a new pentacyclic fused-rings system. The carboamination step was performed also under carbonylative conditions providing the imidazo[1,5-a]indole derivative bearing an enone moiety.
An unusual different outcome was observed when working in the absence of the aryl iodide. This activation led to an interesting hydroamination process, rarely reported in the presence of palladium complexes.2
This reaction proceeded exclusively under microwave irradiation
Reazioni domino promosse da Pd(II)/CuCl2 per la sintesi di morfoline variamente sostituite
No full textLe reazioni che decorrono con la formazione di più legami attraverso processi domino negli ultimi anni hanno assunto sempre più interesse anche nell’ambito delle reazioni catalizzate da palladio.2 Utilizzando diverse condizioni rispetto a quelle utilizzate per accedere a 3,4-diidro-2H-1,4-ossazine, è stato possibile promuovere processi di alcossi-carbonilazione, alcossi-arilazione e azido-alcossilazioni per la formazione di derivati morfolinici diversamente sostituiti. Come visualizzato nello Schema, un ruolo cruciale è occupato dall’ossidante, infatti solo il CuCl2 è in grado di inibire il processo di -eliminazione. Alcune di queste metodologie sono state estese a substrati otticamente attivi
Novel intramolecular cyclization of N-alkynyl heterocycles containing proximate nucleophiles
No full textIntramolecular cyclization of 2-acyl-1-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleu
Intramolecular Oxidative Pd(II)-Catalyzed Alkoxylation of 3-Aza-5-alkenols with O2 as Sole Oxidant: Mild Conditions for the Synthesis of 1,4-Oxazine Derivatives
No full textSynthesis of 1,4-2H-oxazine derivatives was performed by Pd(II)-catalyzed aerobic oxidative cyclization of 3-aza-5-alkenols, prepared from easily available 1,2-amino alcohols. The reaction proceeds in very mild conditions with a simple catalytic system consisting of PdCl2(MeCN)2 in THF at room temperature with molecular oxygen as the sole stoichiometric oxidant
Intramolecular Heck reaction of 2- and 3-iodoindole derivatives for the synthesis of beta- and gamma-carbolinones
No full textA new synthesis of beta- and gamma-carbolinone derivatives was achieved by an intramolecular Heck cyclisation from the corresponding 3-iodo-1H-indole-2-carboxylic acid allyl-amides 8 and 2-iodo-1H-indole-3-carboxylic acid allyl-amides 9. (C) 2002 Elsevier Science Ltd. All rights reserved
SINTESI DI PIRAZINO[1,2-a]INDOLI TRAMITE REAZIONI DI CICLIZZAZIONE INTRAMOLECOLARE DI 2-ACIL-1-PROPARGIL INDOLI
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