1,720,965 research outputs found
The renaissance of strained 1-azabicyclo[1.1.0]butanes as useful reagents for the synthesis of functionalized azetidines
No full textSince their discovery in the late 1960s, 1-azabicyclo[1.1.0]butanes have demonstrated to be interesting precursors of azetidines, because of the peculiar reactivity of the C3-N bond that allows double functionalization in the 1,3 positions. In particular, the recent advances reported by Baran, Lopchuk, Aggarwal, and others witness the synthetic relevance of such strained azabicycles in the synthesis of highly functionalized azetidines. However, the synthesis and reactivity of 1-azabicyclo[1.1.0]butanes remains a poorly explored topic in organic chemistry. This review aims to furnish a comprehensive knowledge on the preparation of 1-azabicyclo[1.1.0]butanes and the transformation into functionalized saturated four-membered azacycles
Continuous Flow Generation of Highly Reactive Organometallic Intermediates: A Recent Update
Get PDFReactive organometallic intermediates present a distinct opportunity for the creation of novel carbon-carbon and carbon-heteroatom bonds. Whereas their utility in synthesis is well-established, the thermal sensitivity of these species often imposes the requirement for stringent reaction conditions, including strict control of reaction temperatures, concentrations, and use of additives. Moreover, their strong reactivity can pose challenges in achieving the desired selectivity. Since pioneering works in the 2000s, the advent of flow microreactor technology has revolutionized this field, expanding the possibilities of reactive organometallic intermediates within synthetic chemistry. In this review, we provide an overview of the recent advancements in this dynamic area, focusing on breakthroughs that have emerged within the past four years
Benchmarking acidic and basic catalysis for a robust production of biofuel from waste cooking oil
Get PDFThe production of biodiesel at the industrial level is mainly based on the use of basic catalysts. Otherwise, also acidic catalysis allowed high conversion and yields, as this method is not affected by the percentage of free fatty acids present in the starting sample. This work has been useful in assessing the possible catalytic pathways in the production of fatty acid methyl esters (FAMEs), starting from different cooking waste oil mixtures, exploring particularly acidic catalysis. It was possible to state that the optimal experimental conditions required concentrated sulfuric acid 20% w/w as a catalyst, a reaction time of twelve hours, a temperature of 85◦ C and a molar ratio MeOH/oil of 6:1. The role of silica in the purification method was also explored. By evaluating the parameters, type of catalyst, temperature, reaction time and MeOH/oil molar ratios, it has been possible to develop a robust method for the production of biodiesel from real waste mixtures with conversions up to 99%
Hypervalent iodine (III) reagents and ammonia as useful combination for highly chemoselective N-transfer to low-valent organosulfur compounds and amines
Get PDFThe combination of hypervalent iodine (III) reagents and source of ammonia allows the genesis of iodonitrene species able to act as source of electrophilic nitrogen. Ammonia umpolung represents the net-result of this combination. Since the introduction of this method in 2016, important and unprecedented transformations have been discovered. In this short review we report the state of the art in the use of this type of iodonitrene in modern synthesis
Overlooked aza-S(iv) motifs: synthesis and transformations of sulfinamidines and sulfinimidate esters
No full textSignificant advancements have been made in the synthesis of overlooked aza-S(iv) motifs. The accessibility of sulfinamidines and sulfinimidate esters has greatly improved through the recent development of efficient and complementary synthetic strategies. Intriguingly, new discoveries have emerged regarding the reactivity of these substances, highlighting the electrophilic nature of sulfinimidate esters and the nucleophilic character of sulfinamidines. Moreover, sulfinamidines have been found to be prone to oxidation, leading to the formation of important aza-S(vi) derivatives. In this review, our aim is to present an almost comprehensive overview of the most relevant achievements in the preparation and structural characterization of these overlooked compounds
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Flow technology enabled preparation of C3-heterosubstituted 1-azabicyclo[1.1.0]butanes and azetidines: accessing unexplored chemical space in strained heterocyclic chemistry
No full textThe use of flow technology as an enabling tool for accessing 1-azabicyclo[1.1.0]butanes bearing strained 3-, 4-, and 5-membered O-heterocycles with C3(N-het)-C2(O-het) connectivity is reported. Reactivity and chemoselectivity (N-ring vs. O-ring) were also evaluated. New chemical space has been explored and new structural motifs such as ABB-aziridines or spiro azetidine-oxazetidines are also reported
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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