1,720,972 research outputs found
Alternative approaches to heterocyclic compounds through new developments of domino transition-metals catalysed and/or Lewis acids promoted reactions
No full textThe aim of the project is based on the development of alternative synthetic methodologies in order to
obtain heterocyclic compounds of interest in biological and pharmacological fields. In particular,
homogeneous and heterogeneous transition-metal catalysts and/or Lewis acids will allow the
development of domino and multi-component reactions devoted to the preparation of heteropolyciclic
rings through domino coupling/regioselective annulation reactions starting from alkynes/alkenes
containing proximate nucleophiles as suitable building blocks. Among the variety of new synthetic transformations, transition metal-catalysed reactions are some of
the most attractive methodologies for synthesising heterocyclic compounds, because a transition metal
catalysed reaction can directly construct complicated molecules from readily accessible starting
materials under mild conditions. Moreover, organometallic intermediates are useful for synthesising
organic compounds which are difficult to obtain through traditional methods and/or are responsible
for regio-, stereo-, and chemoselectivity. In contrast with classical synthetic procedures which involve
multistep synthetic operations, transition metal-catalysed reactions are often domino processes which
lead to the facile creation of several new covalent bonds in a one-pot procedure or can accomplish the
coupling of three or more simple and flexible building blocks in a multicomponent reaction.
Besides, starting from suitable and reactive substrates, domino transformation can be easily achieved
under mild reaction conditions without catalysts, in presence of Lewis acids or promoters that can act
both as Lewis acids and transition metals. Many new procedures based on transition metal complexes
or other suitable catalysts have been developed to obtain heterocycles by C-C and C-N bond formation
with maximal conversion of the reagents and minimal generation of by-products starting from
substrates that are readily available and generally easy to handle. In the field of metal catalysed-reactions our research group focused the attention toward the families of
transition metals and Lewis acids. In the first case we were attracted by the high versatility and activity
of palladium, rhodium, and gold salts and complexes in cross-coupling reactions and multiple bonds
activation. Moreover, we considered the family of Lewis acids using titanium, indium and gallium salts
with their feature to activate both carbon-carbon and carbon-heteroatom multiple bonds.
Moreover, metal-mediated reactions have been mainly applied to the domino/multicomponent
synthesis of heterocyclic compounds from substrates characterised by the presence of an alkyne and a
proximate nucleophile. These compounds demonstrated to be suitable building blocks for the synthesis
of relevant heterocyclic scaffolds
SYNTHESIS OF α-CARBOLINE DERIVATIVES THROUGH A DOMINO AMINATION/C-H DIRECT ARYLATION STRATEGY
No full textREAZIONI di CICLOADDIZIONE [4+2] tra 2-VINILINDOLI e CARBODIENOFILI ACICLICI
No full textLe reazioni di cicloaddizione [4+2] tra 2-vinilindoli e carbodienofili aciclici rappresentano una via sintetica molto importante per la sintesi di carbazoli come building blocks di alcaloidi. Recentemente, partendo da un nuovo 2-indoliltriflato, attraverso una reazione di cross-coupling Pd-catalizzata, abbiamo realizzato una nuova ed efficiente sintesi di indoli protetti all'azoto, recanti un gruppo vinilico in posizione 2 e non sostituiti in posizione 3. La reattività dei 2-vinilindoli è stata saggiata in reazioni di Diels-Alder con semplici dienofili attivati a catena aperta per l'ottenimento di derivati tetraidrocarbazolici. I derivati carbazolici diastereoisomeri sono stati ottenuti in rapporto variabile e dipendente dal pattern di sostituzione dei reagenti. Il lavoro è stato poi esteso utilizzando come dienofili alfa,beta-deidroamminoacidi e indoli non protetti all'azoto al fine di ottenere, anche in maniera enantioselettiva, amminoacidi non naturali a struttura ciclica di potenziale interesse farmacologico
Selective Base Promoted Synthesis of Dihydroisobenzofurans by Domino Addition/ Annulation Reactions of ortho-Alkynylbenzaldehydes
No full textThe synthesis of dihydroisobenzofuran nucleus was achieved by the base promoted tandem nucleophilic addition/
annulation reaction of ortho-alkynylbenzaldehydes in the presence of methanol. The reactions of aryl-, trimethylsilyl- and
diethoxymethyl-substituted alkynylbenzaldehydes occurred with
complete regioselectivity in good to excellent yields under microwaves
irradiation. The reactions of alkyl substituted alkynylbenzaldehydes
took place with good yields and high regioselectivity
only when performed at room temperature and in the presence of a
catalytic amount of a gold(III) salt. The plausible reaction mechanisms
involved were discussed. The effect of the substituent at the
alkynyl terminus on the cyclization mode was tentatively rationalized
Knowledge Management and Customised 3D Modelling to Improve Prosthesis Design
No full textThis paper presents a new approach to design lower limb prosthesis focusing the attention on geometrical model issues. The new design approach has been developed within national and international research projects and, at present, “ad hoc” tools to carry out specific tasks are under development. Within this context, an important role is played by product and process knowledge and by specific CAD tools to design the most critical component, the socket. The paper discusses acquisition and formalisation of the knowledge related to the prosthesis design, with particular attention to the socket, and presents main features of a CAD tool specifically intended for this highly customised component
Reazioni domino di addizione/annulazione di chetoacetileni
No full textLe strutture policicliche contenenti un sistema indolico condensato sono il nucleo base di numerose molecole farmacologicamente attive, aventi un’ampia possibilità d’impiego terapeutico (antitumorali, antivirali, antibiotici, PKC inibitori, antifungini). Di recente, con l’intento di ottenere tali sistemi, abbiamo rivolto la nostra attenzione verso le reazioni domino di addizione/annulazione di chetoacetileni.1 Tali reazioni prevedono una ciclizzazione intramolecolare promossa da nucleofili all’ossigeno2 o all’azoto3,4,5 su tripli legami non attivati.
In questo nuovo lavoro abbiamo valutato la percorribilità di nuove vie sintetiche per l’ottenimento di indoli ciclizzati in posizione 1,2 o 2,3 attraverso attacco di nucleofili al carbonio. All’iniziale formazione dell’enammina, terminale nucleofilo del sistema, fa seguito la reazione di carbociclizzazione che porta alla formazione del nucleo policlico
FROM DOMINO TO MULTICOMPONENT: Pd-ASSISTED SYNTHESIS OF DIHYDROISOBENZOFURANS
No full textMulticomponent reactions (MCRs) are a powerful tool for the synthesis of complex molecules starting from ready available building blocks in a “well-contrived” one-pot sequential procedure.1 The dihydroisobenzofuran nucleus is the core of some important biologically active molecules.2 We recently reported3 a selective synthesis of the dihydroisobenzofuran skeleton through a microwave promoted domino addition/annulation reaction of 2-alkynylbenzaldehydes with methanol in the presence of a suitable base (Scheme 1, pathway A). The approach involves two different steps with a few common requirements: the presence of a base and the needing of an energy source. We were intrigued to simplify and improve the procedure. We found that a variety of substituted dihydroisobenzofuran derivatives can be easily synthesized in high yield by a microwave-assisted three-component approach4 starting from o-bromoarylaldehydes, methanol and terminal alkynes (Scheme 1, pathway B). The reaction occurs through an unprecedented cooperative palladium/base promoted coupling/addition/cyclization sequence
A MICROWAVE-PROMOTED APPROACH TO ISOBENZOFURANS AND ISOQUINOLINES BY TANDEM ADDITION/ANNULATION OF o-ALKYNYLBENZALDEHYDES
No full textLewis Acid Mediated Aminobenzannulation Reactions of δ-Ketoalkynes: Synthesis of 1-Aminocarbazoles and 9-Aminopyrido[1,2-a]indoles
No full text2-Acyl-N-propargylindoles 1 and 2-acyl-3-propargylindoles 5 undergo aminobenzannulation reactions with pyrrolidine in the presence of an appropriate Lewis acid to give 9-aminopyrido[1,2-a]indoles 6 and 1-aminocarbazoles 7, respectively. The selection of the appropriate Lewis acid, TiCl4 or GaCl3 for 1 and InCl3 for 5, allows the domino process involving the initial formation of an enamine intermediate, followed by a regioselective 6-exo-dig intramolecular nucleophilic attack of the nucleophilic terminus of the unsaturated system (the β-carbon of the enamino moiety) to the carbon–carbon triple bond. Moreover, several features concerning the reaction mechanism and the role of both catalysts, in connection with the electronic properties of the reacting alkynes, are reporte
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