324 research outputs found
The CeCl3 Lewis Acid Promoter in the Stereoselective Construction of Carbon-Carbon Double Bonds
No full textThe presence of a C-C double bond in polyfunctionalized organic molecules is a crucial requirement
for the control of its biologically activity.(1) The importance of having a site in the molecule that is
able to generate geometrical isomerization of a carbon-carbon double bond stimulated the
development of new olefination methodologies. In particular, some efforts focused on the ability of
Lewis acids to provide a cheap alternative for the synthesis of molecules with C-C double bond in a
highly stereoselective fashion.
For several years, we have been investigating CeCl3 promoted organic reactions. This Lewis acid has
been found to efficiently promote carbon-carbon (2) and carbon-heteroatom bond formation
reactions.(3) In addition to being green in nature (4), CeCl3 has been widely used for both inter- and
intramolecular reactions for the synthesis of organic molecules with significant biological
importance.
Regarding the total synthesis of biologically active small molecules containing a carbon-carbon
double bond, we saw the possibility to employ CeCl3 in the stereoselective construction of 2,3-
dihydropyridones 1,(5) and 1,2-dihydroquinolines 2.(6)
The additional advantage of using CeCl3 in a reaction includes its selectivity and tolerance in the
presence of other functional groups. For instance, it can be used during the functionalization of
molecules at late stage involving complex molecules or undesirable use of protecting groups.
Introduction of C-C double bonds, which are known to increase the activity in macrolides against
bacterial RNA polymerase, is currently in progress in our laboratory.
References: 1. Shen, X.; Nguyen, T. T.; Koh, M. J.; Xu, D.; Speed, A. W.; Schrock, R. R.; Hoveyda, A. H. Nature 2017,
541, 380-385. 2. Bartoli, G.; Marcolin, M.; Sambri, L.; Marcantoni, E. Chem. Rev. 2010, 110, 6104-6143. 3. Properzi, R.
Marcantoni, E. Chem. Soc. Rev. 2014, 43, 779-791. 4. Cimarelli, C.; Di Nicola, M.; Diomedi, S.; Giovannini, R.;
Hanprecht, D.; Properzi, R.; Sorana, F.; Marcantoni, E. Org. Biomol. Chem. 2015, 13, 11687-11695. 5. Bordi, S.;
Cimarelli, C.; Lupidi, G.; Marsili, L.; Piermattei, P.; Marcantoni, E. J. Org. Chem. 2017, in preparation. 6. Cimarelli, C.;
Bordi, S.; Piermattei, P.; Pellei, M.; Del Bello, F.; Marcantoni, E. Tetrahedron 2017, submitted
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
Moiré patterns generated by stacked 2D lattices: A general algorithm to identify primitive coincidence cells
No full textTwo-dimensional materials on metallic surfaces or stacked one on top of the other can form a variety of moiré superstructures depending on the possible parameter and symmetry mismatch and misorientation angle. In most cases, such as incommensurate lattices or identical lattices but with a small twist angle, the common periodicity may be very large, thus making numerical simulations prohibitive. We propose here a general procedure to determine the minimal simulation cell which approximates, within a certain tolerance and a certain size, the primitive cell of the common superlattice, given the two interfacing lattices and the relative orientation angle. As case studies to validate our procedure, we report two applications of particular interest: the case of misaligned hexagonal/hexagonal identical lattices, describing a twisted graphene bilayer or a graphene monolayer grown on Ni(111), and the case of hexagonal/square lattices, describing for instance a graphene monolayer grown on Ni(100) surface. The first one, which has also analytic solutions, constitutes a solid benchmark for the algorithm; the second one shows that a very nice description of the experimental observations can be obtained also using the resulting relatively small coincidence cells
Efficient Lewis Acid Systems for the A3 Coupling reaction
No full textEfficient Lewis Acid Systems for the A3 Coupling reaction
Cimarelli C., a Navazio F.,a Rossi F. V.a, Del Bello F., Marcantoni E.a
aSchool of Science and Technology, Chemistry Division, University of Camerino, Via S. Agostino 1, 62032 Camerino; e-mail: [email protected]
Propargylamines are an attractive class of molecules because of their particular molecular skeleton, that contains an amine group located in β-position to an alkyne moiety suitable for many chemical transformations. In recent years they received a growing interest as key intermediates for several biologically active compound, natural products and also different heterocycles.[1,2]
Our goal was the development of green and simple methodologies for the synthesis of secondary propargylamines by Lewis acid catalyzed or promoted A3 reaction among aldehydes, alkynes and primary amines, that are in general less applied in such reactions because of their lower reactivity. In particular, we studied two different pathway: the CuSO4/NaI system in one pot fashion and the CeCl3/CuI system in one pot/two steps way (Scheme 1).
Scheme 1. CeCl3·7H2O/CuI and CuSO4/NaI catalyzed A3 reaction.
Heptahydrated CeCl3 is reported to be an excellent catalyst for many useful organic transformation as the synthesis of imines. Its efficacy as Lewis acid is enhanced in the presence of inorganic iodides/iodide salt and being cooper the transition metal of choice for A3 reactions, CuI was used.[3]
Also the CuSO4/NaI couple has revealed to be an interesting Lewis acid system as an alternative to CeCl3/CuI system which allow the formation of CuI in situ by quantitative spontaneous reaction that takes place in few seconds.[4]
Typically CuSO4/NaI catalysed reactions are faster than CeCl3·7H2O/CuI reactions, but suffer of some disadvantages, such as lower yields, and a narrower applicability. Both reaction conditions have been applied to different aldehydes (aromatic and aliphatic) and to chiral starting materials, the amine in general has no effect on the reaction outcome.
The relevant Glaser coupling drawback observed in the CuSO4/NaI system conditions has been suppressed by adding some benzoic acid, and has not been observed with the CeCl3/CuI system.
References:
1) Lauder, K.; Toscani, A.; Scalacci, N.; Castagnolo, D. Chem. Rev. 2017, 117, 14091.
2) Peshkov, V. A.; Pereshivko, O. P.; Van der Eycken, E. V. Chem. Soc. Rev. 2012, 41, 3790.
3) G. Bartoli, E. Marcantoni, M. Marcolini, L. Sambri, Chem. Rev. 2010, 110, 6104.
4) Bailey, A. D.; Cherney, S. M.; Anzalone, P. W.; Anderson, E. D.; Ernat, J. J.; Mohan, R. S. Synlett 2006, 215
Qubit entanglement generation by Gaussian non-Markovian dynamics
No full textWe consider two qubits interacting with a common bosonic bath, but not directly between themselves.
We derive the (bipartite) entanglement generation conditions for Gaussian non-Markovian dynamical maps and show that they are similar as in the Markovian regime; however, they depend on different physical coefficients and hold on different time scales. Indeed, for small times, in the non-Markovian regime entanglement is possibly generated on a shorter time scale (/ t2) than in the
Markovian one (/ t). Moreover, although the singular coupling limit of non-Markovian dynamics yields Markovian ones, we show that the same limit does not lead from non-Markovian entanglement generation conditions to Markovian ones. Also, the entanglement generation conditions do not depend on the initial time for non-Markovian open dynamics resulting from couplings to bosonic
Gaussian baths, while they may depend on time for open dynamics originated by couplings to classical, stochastic Gaussian environments
Qubit entanglement generation by Gaussian non-Markovian dynamics
No full textWe consider two qubits interacting with a common bosonic bath, but not directly between themselves. We derive the (bipartite) entanglement generation conditions for Gaussian non-Markovian dynamical maps and show that they are similar as in the Markovian regime. However, they depend on different physical coefficients and hold on different time scales. Indeed, for small times, in the non-Markovian regime entanglement is possibly generated on a shorter time scale (α t2 ) than in the Markovian regime (α t). Moreover, although the singular coupling limit of non-Markovian dynamics yields Markovian ones, we show that the same limit does not lead from non-Markovian entanglement generation conditions to Markovian ones. Also, entanglement generation conditions do not depend on the initial time for non-Markovian open dynamics resulting from couplings to bosonic Gaussian baths, while they may depend on time for open dynamics originated by couplings to classical, stochastic Gaussian environments
Self-cleaning composite material, in particular a composite material for production of molded items for kitchen and bathroom interior decoration
No full textA self-cleaning composite material comprising the following composition is disclosed: 65-80% in weight of quartzbased
mineral extenders; 2-15% in weight of fme particles of silicate family, such as wollastonite, calcium silicate, cristobalite, silica
(SiOz), with size lower than 0.1 mm; 5-20% of glass microspheres, with grain size lower than 212 micron; 10-25% of methacrylic syrup composed of one monomer and one polymer; photocatalytic titanium oxide (TiOz) dispersed in methacrylic syrup in weight percentage of 0.05-5% with respect to the weight of the methacrylic syrup; coupling agent to obtain anchoring of photocatalytic Ti02 to methacrylic syrup; and cross-linking monomers to obtain reticulation of methacrylic syrup
Thermodynamics of a qubit undergoing dephasing
No full textThe thermodynamics of a qubit undergoing dephasing due to the coupling with the external environment is discussed. First of all, we assume the dynamics of the system to be described by a master equation in Lindblad form. In this framework, we review a standard formulation of the first and second law of thermodynamics that has been known in literature for a long time. After that, we explicitly model the environment with a set of quantum harmonic oscillators choosing the interaction such that the global dynamics of system and bath is analytically solvable and the Lindblad master equation is recovered in the weak-coupling limit. In this generalized setting, we can show that the correlations between system and bath play a fundamental role in the heat exchange. Moreover, the internal entropy production of the qubit is proven to be positive for arbitrary coupling strength
Recent Developments in Chemical Derivatization of Microcrystalline Cellulose (MCC): Pre-Treatments, Functionalization, and Applications
No full textMicrocrystalline Cellulose (MCC) is an isolated, colloidal crystalline portion of cellulose fibers, and it is a valuable alternative to non-renewable fossil-based materials. It is used for a large plethora of different fields, such as composites, food applications, pharmaceutical and medical developments, and cosmetic and material industries. The interest of MCC has also been driven by its economic value. In the last decade, particular attention has been driven to the functionalization of its hydroxyl groups to expand the field of applications of such biopolymer. Herein, we report and describe several pre-treatment methods that have been developed to increase the accessibility of MCC by breaking its dense structure allowing further functionalization. This review also collects the results that have appeared in the literature during the last two decades on the utilization of functionalized MCC as adsorbents (dyes, heavy metals, and carbon dioxide), flame retardants, reinforcing agents, energetic materials, such as azide- and azidodeoxy-modified, and nitrate-based cellulose and biomedical applications
Enantioselective α-Benzoyloxylation of Ketones Promoted by Primary Amine Catalyst
No full textA mixture of 9-amino-(9-deoxy)epi-dihydroquinidine and salicylic acid was able to promote the direct reaction of various cyclohexanones with dibenzoyl peroxide, thus affording the corresponding protected α-hydroxy carbonyl compounds in high yield and enantioselectivity. Interestingly the same catalytic salt was found to be active when 1-indanones derivatives were directly employed in the reaction with dibenzoyl peroxide furnishing chiral 1-oxo-2,3-dihydro-1H-inden-2-yl benzoates in high yields and enantioselectivity. Furthermore their treatment with NaBH4 gives easy access to the corresponding enantioenriched 1,2-diols in high yields and without any loss of stereoselectivity
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