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Recent advances in transition metal-catalysed hydroacylation of alkenes and alkynes
Get PDFThis highlight discusses developments in transition metal-catalysed alkene and alkyne hydroacylation reactions over the past three years. The discussion summarizes the development of new catalyst systems for alkene and alkyne hydroacylation and applications to the synthesis of important ketone building blocks. The highlight captures transition metal-catalysed alkene and alkyne hydroacylation at a time of impressive growth when cobalt, nickel, ruthenium, and iridium catalysts are emerging as complements or replacements for traditional rhodium catalysts.This article is published as Ghosh, Avipsa, Kirsten F. Johnson, Kevin L. Vickerman, James A. Walker, and Levi M. Stanley. "Recent advances in transition metal-catalysed hydroacylation of alkenes and alkynes." Organic Chemistry Frontiers 3, no. 5 (2016): 639-644. doi: 10.1039/C6QO00023A. Posted with permission.</p
A Biphilic Phosphetane Catalyzes N–N Bond-Forming Cadogan Heterocyclization via P[superscript III]/P[superscript V]═O Redox Cycling
No full textA small-ring phosphacycle, 1,2,2,3,4,4-hexamethylphosphetane, is found to catalyze deoxygenative N-N bond-forming Cadogan h eterocyclization of o-nitrobenzaldimines, o-nitroazobenzenes, and related substrates in the presence of hydrosilane terminal reductant. The reaction provides a chemoselective catalytic synthesis of 2H-indazoles, 2H-benzotriazoles, and related fused heterocyclic systems with good functional group compatibility. On the basis of both stoichiometric and catalytic mechanistic experiments, the reaction is proposed to proceed via catalytic P[superscript III]/P[superscript V] = O cycling, where DFT modeling suggests a turnover-limiting (3+1) cheletropic addition between the phosphetane catalyst and nitroarene substrate. Strain/distortion analysis of the (3+1) transition structure highlights the controlling role of frontier orbital effects underpinning the catalytic performance of the phosphetane.National Institute of General Medical Sciences (U.S.) (Award GM114547)Alfred P. Sloan FoundationAmgen Inc
ChemInform Abstract: Enantioselective Hydroacylation of N‐Vinylindole‐2‐carboxaldehydes.
Get PDFWe report catalytic, enantioselective intramolecular hydroacylation of N-vinylindole-2-carboxaldehydes. These hydroacylation reactions occur in the presence of a readily accessible rhodium catalyst and form chiral, non-racemic 2,3-dihydro-1H-pyrrolo[1,2-a]indol-1-ones in high yields with excellent enantioselectivities.This is a manuscript of an article published as Ghosh, Avipsa, and Levi M. Stanley. "Enantioselective hydroacylation of N-vinylindole-2-carboxaldehydes." Chemical Communications 50, no. 21 (2014): 2765-2768. doi: 10.1039/C4CC00210E. Posted with permission.</p
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
Transition Metal-Catalyzed Alkene Hydroacylation as a Platform for Enantioselective Synthesis of Polycyclic Nitrogen Heterocycles
Get PDFThe prevalence of nitrogen heterocycles in medicinally important compounds has, for years, inspired synthetic chemists for developing strategies to form new heterocyclic scaffolds and methods that streamline the syntheses of complex heterocycles. Giving into the cause, this dissertation primarily focuses on development of transition-metal catalyzed hydroacylation of alkenes as a platform for enantioselective synthesis of multiple classes of polycyclic nitrogen heterocycles.
Development of catalytic, enantioselective intramolecular hydroacylation of N-vinylindole-2-carboxaldehydes that occur in the presence of a readily accessible rhodium catalyst and form chiral, non-racemic 2,3-dihydro-1H-pyrrolo[1,2-a]indol-1-ones in high yields and enantioselectivities has been described. The dihydropyrroloindolone products can be readily transformed to dihydropyrroloindoles that are core structures present in a variety of natural products and biologically relevant compounds. This methodology could be extended to hydroacylations of N-allylindole- and N-allylpyrrole-2-carboxaldehydes in construction of six-membered rings that generated 7,8-dihydropyrido[1,2-a]indol-9(6H)ones and 6,7-dihydroindolizin-8(5H)-ones in moderate to high yields with excellent enantioselectivities. In contrast to many alkene hydroacylations that form six-membered rings, these endo-selective annulative processes occur in the absence of ancillary functionality to stabilize the acylrhodium(III) hydride intermediate.
Our protocol for rhodium-catalyzed hydroacylation of N-vinylindole-2-carboxaldehyde could be leveraged for installation of stereochemical triad in 2,3-dihydro-1H-pyrrolo[1,2-a]-indole core of putative structure of yuremamine. The enantioselective model synthesis was achieved in 39% overall yield and 96% ee over 5 steps. An enantioselective synthesis of a densely functionalized dihydropyrroloindolone that maps onto the putative structure of yuremamine is demonstrated in 26% yield and 97% ee over 8 steps.
Additionally, exo-selective nickel- and NHC-catalyzed hydroacylations could be coupled with catalytic enantioselective -(hetero)arylation reactions in a sequential synthetic strategy to form a wide variety of nitrogen-containing heterocyclic ketones bearing -chiral quaternary stereogenic centers. Exo-selective, intramolecular Ni-catalyzed hydroacylations of N-homoallylindole- and N-homoallylpyrrole-2-carboxaldehydes form -substituted six-membered heterocyclic ketones in up to 95% yield, while N-heterocyclic carbene (NHC)-catalyzed hydroacylations of N-allylindole- and N-allylpyrrole-2-carboxaldehydes form -substituted five-membered heterocyclic ketones in up to 99% yield. The racemic five- and six-membered products of Ni- and NHC-catalyzed hydroacylation reactions are readily transformed into heterocyclic ketones containing an -chiral quaternary stereogenic center by enantioselective Ni-catalyzed -arylation and -heteroarylation reactions. The identity of the precatalyst for Ni-catalyzed -(hetero)arylation is dictated by the identity of the –substituted heterocyclic ketone starting material. -(Hetero)arylations of six-membered heterocyclic ketones occur at 65-85 à °C in the presence of a catalyst generated in situ from Ni(COD)2 and (R)-BINAP or (R)-DIFLUORPHOS. -(Hetero)arylation of five-membered heterocyclic ketones must be conducted at room temperature in the presence of an [((R)-BINAP)Ni(2-NC-Ph)] precatalyst or a catalyst generated in situ from Ni(COD)2, (R)-DIFLUORPHOS and benzonitrile.
Finally, studies on Ni2P nanocrystal catalyzed hydrogenation of phenylacetylene have been reported. The model reaction is studied with both hollow and solid Ni2Ps in two different solvents (1,4-dioxane and 1-propanol). Recycling studies in both solvents demonstrated increase in catalytic activity of Ni2P nanocrystals over reaction cycles. Structural characterization of recycled Ni2P nanocrystals via powder XRD, TEM and XPS analyses revealed reduction in size of hollow nanoparticles along with the formation of Ni(II) species after hydrogenation reactions. Systematic characterization of Ni2P nanocrystals isolated after each reaction throughout the lifetime of recycling study (in both 1,4-dioxane and 1-propanol) has been demonstrated.</p
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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