991 research outputs found
PERCHLORATES AS POWERFUL CATALYSTS IN MANY IMPORTANT ORGANIC TRANSFORMATIONS
No full textFor long times, metallic perchlorates have been considered dangerous compounds[1] in that they function as explosives and as incontrollable oxidizers.
Therefore, the fear of the great hazard connected with their manufacture and uses had prevented an extensive use both in research laboratories and in industrial processes.[2]
However, recently it has been cleared that this bad reputation is due to the mistaken association of metallic perchlorates with the oxidizing potential of perchloric acid and the pyrotechnic performances of NH4ClO4.
In this conference, we report that Magnesium and Zinc perchlorates can be used as powerful Lewis acids in several organic transformations which are commonly employed both in laboratory and industrial processes.
As depicted in the Scheme, perchlorates are able to promote a series of reactions such as:
a) Acylation of alcohols[3,4]
b) Fisher esterification[5]
c) Synthesis of b–enamino esters[6]
d) Protection of the amino group as N-Boc derivative[7]
Moreover, they can act as specific catalysts for the development of a new organic transformations. In fact, the treatment of an alcohol or a phenol with Boc2O in the presence of Mg(ClO4)2 leads to the unexpected formation of the corresponding t-butyl ethers.[8] This represents the first general method to synthesize aromatic t-butyl ethers.
In an analogous manner, the treatment of phenols with diethyl dicarbonate results in a very efficient method to produce difficulty available aryl ethyl carbonates.
Several of the above mentioned transformations can be carried out in the absence of the solvent, and often the catalyst can be easily recovered and reused without an appreciable loss of activity.
Acknowledgement
Work carried out in the framework of the National Project “Stereoselezione in Sintesi Organica. Metodologie e Applicazioni” supported by MIUR, Rome, by the University of Bologna, in the framework of “Progetto di Finanziamento Pluriennale, Ateneo di Bologna”, and by National project FIRB “Progettazione, preparazione e valutazione biologica e farmacologica di nuove molecole organiche quali potenziali farmaci”
References
[1] Schumacher, J. C. Perchlorates-Their Properties, Manufacture and Uses, ACS Monograph Series, Reinhold: New York, 1960.Author. Title[J]. Name of the journal, Year, Volume(Issue): initial page and ending page (Optional).
[2] Long, J. Chemical Health & Safety, 2002, 9, 12.
[3] Bartoli, G.; Bosco, M.; Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.; Rinaldi, S.; Sambri, L. Synlett, 2003, 39.
[4] Bartoli, G.; Bosco, M.; Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.; Sambri, L. Eur. J. Org. Chem. 2003, 4611.
[5] a) Gooβen, L.; Döhring, A. Adv. Synth. Catal. 2003, 345, 943; b) Bartoli, G.; Boeglin, J.; Bosco, M.; Locatelli, M.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Adv. Synth. Catal. 2005, 347, 33.
[6] Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Melchiorre, P.; Sambri, L. Synlett 2004, 239.
[7] Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Synlett 2004, 1794.
[8] Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Melchiorre, P.; Sambri, L. Org. Lett., 2004, 7, 427
APPLICATIONS OF PERCHLORATES IN ORGANIC SYNTHESIS. A NEW AND GENERAL ROUTE TO t-BUTYL ETHERS
No full textAPPLICATIONS OF PERCHLORATES IN ORGANIC SYNTHESIS. A NEW AND GENERAL ROUTE TO t-BUTYL ETHERS
Giuseppe Bartoli, Marcella Bosco, Manuela Locatelli, Paolo Melchiorre and Letizia Sambri
Dipartimento di Chimica Organica “A. Mangini”, v.le Risorgimento 4, Bologna, Italy
[email protected]
In the last few years, we were interested in the use of various metallic perchlorates as Lewis acid promoters in various organic transformations.1 In particular, perchlorate salts have shown a high ability to activate 1,3-dicarbonyl systems.
We surprisingly found that anhydrous Mg(ClO4)2 promotes the reaction of alcohols with t-butyl dicarbonate (Boc2O) to give t-butyl ethers.2 This reaction appears extremely interesting, as it represents a potential solution to a longstanding problem in organic synthesis namely, t-butyl ether formation. The t-butyl ether in fact is “one of the most underused alcohol protecting groups”,3 although it is one of the few ethers stable under strongly basic conditions.
We set up a new protocol for the synthesis of t-butyl ethers from a large variety of functionalized aromatic and aliphatic alcohols. Selective mono-protection of symmetric and asymmetric diols can also be achieved.
At the same time, a convenient deprotection protocol was set up. In fact, t-butyl ethers were easily reconverted in the corresponding alcohols by simple treatment with the CeCl3/NaI system.4
Scheme 1.
1. Bartoli, G.; Boeglin, J.; Bosco, M.; Locatelli, M.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Adv. Synth. Catal. 2005, 347, 33-38. and references herein cited.
2. Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Melchiorre, P.; Sambri, L. Org. Lett. 2005, 7, 427-430.
3. Greene, T. W.; Wuts, P. G. M in Protective Groups in Organic Synthesis, Wiley, New York, 3rd Ed., 1999, pp. 65-67.
4. Bartoli, G.; Marcantoni, E.; Sambri, L. Synlett, 2003, 2101-2116
Highly Enantioselective Carbamate-based Aminolytic Kinetic Resolution (AKR) of Terminal Epoxides
No full textHighly Enantioselective Carbamate-based Aminolytic Kinetic Resolution (AKR) of Terminal Epoxides
P. Melchiorre*, G. Bartoli, A. Carlone, L. Sambri
Department of Organic Chemistry “A. Mangini” - University of BolognaV.le Risorgimento, 4 - 40136 Bologna, ItalyFax +39 051 209 3654, e-mail: [email protected]
Amino alcohol, Asymmetric synthesis, Aziridine, Kinetic resolution, Oxazolidinone
The asymmetric aminolytic kinetic resolution (AKR) of racemic terminal epoxides using carbamates as the nucleophile catalysed by readily available chiral (salen)CoIII complexes affords both aliphatic and aromatic N-Boc or N-Cbz protected 1,2-amino alcohols in almost enantiomerically pure form (ee ≥ 99%).1, 2 The extraordinary high levels of selectivity and the synthetic versatility of the carbamate moiety render the AKR strategy a practical synthetic tool for the direct synthesis of valuable chiral building blocks such as 5-substituted oxazolidinones and N-protected aziridines in enantiomerically pure form starting from inexpensive racemic terminal epoxides. 1. Bartoli, G.; Bosco, M.; Carlone, A.; Locatelli, M.; Melchiorre, P.; Sambri, L. Org. Lett. 2004, 6, 3973.2. For earlier studies involving (salen)Co-catalysed aymmetric ring opening of epoxides, see: Schaus, S. E.; Brandes, B. D.; Larrow, J. F.; Tokunaga, M.; Hansen, K. B.; Gould, A. E.; Furrow, M. E.; Jacobsen, E. N. J. Am. Chem. Soc. 2002, 124, 1307 and references cited therein
Le attività down-stream nel settore dell’energia elettrica e del gas naturale
No full textConcorrenza e regolamentazione nei servizi
pubblici a rete: Il settore dell’energia elettrica dal monopolio pubblico
all’apertura della concorrenza. La trasmissione e il dispacciamento dell’energia elettrica . L’affidamento dell’attività di distribuzione dell’energia elettrica: il regime transitorio. La vendita di energia elettrica. Il trasporto e il dispacciamento del gas naturale. L’attività di distribuzione del gas naturale. L’affidamento del servizio pubblico di distribuzione del gas naturale dal periodo transitorio alle nuove gare. Le gare per ambiti territoriali minimi. I decreti attuativi della riforma. Il contratto di servizio. La durata del regime transitorio applicabile all’attività di distribuzione del gas. Le conseguenze della cessazione anticipata per i vecchi concessionari: la partecipazione alle gare e il rimborso delle immobilizzazioni. Il sistema tariffario per la distribuzione del gas. L’attività di vendita del gas naturale. Gli obblighi di servizio pubblico e l’accesso alla fornitura di
gas. Gli obblighi di separazione societaria, funzionale e contabile
(unbundling
Group 14 metalloles. Properties, synthesis and potential applications: From organic electronics to soft materials
No full textSince the discovery of the aggregation-induced emission (AIE) phenomenon of siloles in 2001, extensive research has been devoted to the synthesis of AIE-active group 14 metalloles and their applications. A large number of new systems have been designed, synthesized, and studied. It has been determined that the restriction of intramolecular rotation is the main cause for AIE, and the effect that the nature of the substituents has on the electronic structures allows one to control the properties of these materials. Siloles hold a number of favourable attributes for application in organic electronics; therefore many applications can be conceived for the siloles and other metalloles. In this mini-review we illustrate recent progress in the development of group 14 metallole-based OLEDs, bio/chemosensors and soft materials
Applications of CeCl3.7H2O-NaI System Towards the Formation of Heterocyclic Structures
No full textApplications of CeCl3·7H2O-NaI system
towards the formation of heterocyclic structures
Enrico Marcantoni,1 Massimo Massaccesi,1 Marino Petrini,1
Giuseppe Bartoli,2 Letizia Sambri2
1 Department of Chemical Sciences, University of Camerino, via S. Agostino 1, I-62032 Camerino (MC), Italy
2 Department of Organic Chemistry “A. Mangini”, University of Bologna,
V.le Risorgimento 4, I-40136, Bologna, Italy
[email protected]
CeCl3·7H2O-NaI system has emerged in the last years as a “friendly” Lewis acid,(1) able to promote a wide range of organic transformations. Its high and specific affinity for O-containing functionalities prompted us to employ such a promoter in the field of heterocyclic chemistry. We present some our recent applications of CeCl3·7H2O-NaI combination directed towards the formation of heterocyclic systems, within an organic synthetic view.
Continuing our work on solvent-free conditions, we found that CeCl3·7H2O-NaI system supported on silica gel promotes the addition of a variety of indoles 1 to nitroalkenes 2, giving 2-indolyl-1-nitroalkanes 3 in good yields.(2) Our methodology was applied to the synthesis of β-carbolines 4, a large group of naturally occurring heterocyclic alkaloids.(3)
The tetrahydro-2H-pyran heterocyclic structure (THP) is frequently used for the protection of alcohols in organic synthesis. We have developed a practical procedure for the introduction of THP group by using the CeCl3·7H2O-NaI system. After screening various reaction conditions, we found that 3,4-dihydro-2H-pyran ring reacts with the hydroxy function in the presence of a catalytic amount of CeCl3·7H2O-NaI, for the conversion of alcohols into the corresponding THP ethers 5. The scope of the reaction was investigated through several examples, which revealed both the chemoselective action of our Lewis acid system and its marked capacity to act as a promoter even in solvent-free conditions.
(1) Bartoli, G.; Marcantoni, E.; Sambri, L. Synlett. 2003, 14, 2101; (2) Bartoli, G.; Bosco, M.; Giuli, S.; Giuliani, A.; Lucarelli, L.; Marcantoni, E.; Sambri, L.; Torregiani, E. J. Org. Chem. 2005, 70, 1941; (3) Cacchi, S.; Fabrizi, G.; Parisi, L. M. Org. Lett. 2003, 5, 3843; Wang, H.; Usui, T.; Osada, H.; Ganesan, A. J. Med. Chem. 2000, 43, 1577
Triple Click to Tripodal Triazole-Based Ligands - Synthesis and Characterization of Blue-Emitting Ce3+Complexes
No full textTris(aryltriazolylmethyl)amine compounds have been synthesized by a one-pot triple click reaction of azides from anilines with tripropargylamine. The resulting tripodal ligands have been employed to obtain six new Ce3+ complexes. The formation of the new complexes, which were obtained both as heteroleptic or homoleptic types, is influenced by the nature of the counterion (nitrate, perchlorate, or triflate) of the starting Ce3+ salts. All the new Ce3+-based complexes are highly stable both in solution and in the solid state. Their structural features have been at first studied by NMR spectroscopy. In addition, by combining experimental and DFT theoretical approaches, the X-ray structure of one heteroleptic complex has been used to simulate the structures of all the remaining complexes. Finally, both the heteroleptic and the homoleptic complexes are luminescent, and the analysis of their photophysical properties indicate that the Ce3+ center regulates the occurrence of radiative processes. A new one-pot triple click reaction leads to tripodal triazole ligands, which are able to coordinate CeIII to give luminescent complexes. Their nature, such as their NMR spectra and photophysical properties, depends on the counteranion. By combining experimental and theoretical approaches, the X-ray structure of one complex is used to simulate the structures of the remaining complexes
Propagation dynamics of a LaMnO3 laser ablation plume in an oxygen atmosphere
No full textThe effect of ambient gas on the expansion dynamics of the plasma plume generated by excimer laser ablation of a LaMnO3 target is investigated by using fast photography. The plume propagation in an oxygen environment is examined with pressure ranging from vacuum to a few millibars. Imaging analysis performed over a complete set of images of the plume emission, for each pressure, has allowed following the changes in the plume structure, the plume front dynamics and stopping length, as well as the variation of plume angular distribution as a function of time and pressure. Our experimental findings evidence a number of interesting effects occurring at various times of the expansion and at different pressure levels. At low pressure (< 10(-2) mbar) the plume expands freely resembling the propagation in high vacuum condition. Then, at intermediate pressure levels (10(-2)-1 mbar) spatial splitting of the plume, plume front oscillations, plume broadening and sharpening, and, finally, plume stopping are observed as a function of the expansion time. The plume stopping length and the asymptotic angular width of the plume as a function of the pressure are analyzed and discussed. The expansion dynamics of the plume front is examined by means of a theoretical description of plume evolution and shock-wave propagation, which considers distance-related pressure dimensionless variables, resulting in a fairly good agreement
1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
No full textPro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process
Versatility of Silicon-based compounds in organic synthesis
No full textOrganosilicon compounds exhibit a multitude of functions in organic synthesis, therefore a plenty of
research has been performed in this field and the interest in these important compounds is still growing.
Organosilanes own many attractive properties. They generally are much more moisture- and air-stable
than various organometallic reagents and can be readily prepared from a wide range of starting
materials. Silicon derivatives have low toxicity and display rich and diverse chemistry that can usually
be rationalized by understanding a relatively small number of fundamental properties of silicon.
The reactivity of organosilanes depends both on steric requirements and electronic contributions.
Silicon is below carbon in the periodic table, but it is capable of very different bonding characteristics.
It is less electronegative than carbon and hydrogen and it forms unusually strong bonds with
electronegative elements of the second period bearing a lone pair of electrons; therefore most of
organosilicon chemistry is driven by the formation of these bonds at the expense of weaker bonds.
In addition, the availability of relatively low energy empty 3d AOs lets Si to allow higher coordination
numbers, forming the so called hypervalent silicon compounds. The ability to expand its valence state
has consequences on the mechanisms of many reactions proceeding at Si.
Silicon can stabilize a positive charge in β-position, and this effect is known as the β-Si effect.3
Moreover, silicon provides stabilization of α-negative charge,4 in fact carbanions with an α-silicon
group are more stable than their carbon analogues.
Since the versatility in reactivity, a wide range of reaction-types involving silicon compounds have
been developed over the years. An exhaustive overview is almost impossible and during this lecture
only some classes of reactions will be covered.
From a synthetic point of view, organosilanes possess many desirable characteristics. In fact, besides
their green character, they can survive under a large variety of reactions and purification conditions,
such as air, moisture, silica-gel, reducing or oxidizing conditions.5 The silyl moiety can be introduced at
almost any stage in the synthesis and can remain unaltered until the appropriate conditions make it
reactive
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