1,721,064 research outputs found
Environmentally Friendly Synthesis of Heterocyclic Polyfunctionalized Molecules Based on CeCl3.7H2O-NaI Promoter.
No full textApplications 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
The Knoevenagel Reaction by CeCl3.7H2O-NaI System: An Efficient Synthesis of Trisubstituted Alkenes.
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Diastereoselective synthesis of tertiary alcohols by nucleophilic addition to a -substituted-b -keto esters,
No full textA protocol of nucleophilic addition to β-keto esters is reported, aimed to the synthesis of tertiary alcohols with high diastereomeric purity. The combined use of organocerium compounds and TiCl4 makes the procedure very efficient and stereoselective with phenyl ketone derivatives. The effect of the nature of the ester function as well as the group bound to the ketone moiety was investigated and rationalized
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Organocerium Reagents
No full textThe nucleophilic addition of an organometallic reagent to multiple bonds is one of the most important strategies to obtain new bonds. The usefulness of this reaction is of marked importance not only for organometallic chemists but also in organic chemistry and in the synthesis of complex organic molecules. However, in spite of its broad utility, their basicity and redox potential sometimes cause serious drawbacks to organometallic reagents. In this scenario, cerium(III) salts, when used as additives in combination with common organometallic reagents such as organolithium or Grignard reagents, emerged as reagents of choice in metal-promoted reactions allowing straightforward formation of carbon-carbon bonds. The reaction with organocerium reagents is now one of most frequently used in academic institutions or in industry because these compounds are environmentally sound compared to other organometallic reagents, and this has been an important aspect of their continued development
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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