1,721,006 research outputs found
Hydroxyselenylation and Tethered Silanoxyselenylation of Allylic Silanols
No full textWe present protocols for the highly regioselective hydroxyselenylation and silanoxyselenylation of allylic
silanols. N-(Phenylseleno)phthalimide acts as the selenylating agent for both transformations. Under basic conditions, hydroxyselenylation proceeds with >20:1 regioselectivity, and the products are valuable synthons for further transformations. We show that the silanol plays a critical role in maintaining the yield and regioselectivity of this reaction. Surprisingly, under acidic conditions, the hydroxyselenylation pathway is blocked, and products of a tethered silanoxyselenylation are exclusive
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
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
Hydroxyselenylation and Tethered Silanoxyselenylation of Allylic Silanols
No full textWe
present protocols for the highly regioselective hydroxyselenylation
and silanoxyselenylation of allylic silanols. N-(Phenylseleno)phthalimide
acts as the selenylating agent for both transformations. Under basic
conditions, hydroxyselenylation proceeds with >20:1 regioselectivity,
and the products are valuable synthons for further transformations.
We show that the silanol plays a critical role in maintaining the
yield and regioselectivity of this reaction. Surprisingly, under acidic
conditions, the hydroxyselenylation pathway is blocked, and products
of a tethered silanoxyselenylation are exclusive
Peroxydisulfate as an Oxidant in the Site-Selective Functionalization of sp<sup>3</sup> C-H Bonds
No full textAppropriate 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
A Study of Alkene Disulfonoxylation
No full textWe have developed convenient protocols for alkene disulfonoxylation, which involve stirring alkene substrate with a commercial I(III) oxidant and sulfonic acid in CH2Cl2 at ambient temperature. The reactions can be performed open to air without any special precautions to exclude moisture and, in most cases, deliver the products of vicinal disulfonoxylation. Where relevant, the reactions are stereospecific and furnish the products of syn-disulfonoxylation. Our protocols work best with terminal alkene substrates, but other substitution patterns are also compatible. With alkene substrates bearing appropriately positioned esters, sulfonoxylated lactones are the major products. With certain styrenyl alkenes, the products of geminal disulfonoxylation are exclusive. For this last reaction type, our results suggest that literature reports of related transformations contain misassigned product structures
Sulfamate Tethered Aza-Wacker Strategy for a Kasugamine Synthon
No full textWe present our preparation of a kasugamine synthon, which proceeds in 14 steps from a literature epoxide. We expect
that this kasugamine derivative can be used for the total syntheses of kasugamycin, minosaminomycin, and analogue antibiotics. A key step in the synthesis is our laboratory’s sulfamate-tethered aza-Wacker cyclization
Intramolecular Silanoxy-Michael Reactions with Pendant Nitroalkenes, Racemic and Enantioselective
No full textWe present the first racemic and scalemic examples of di-tert-butyl silanoxy Michael additions. Our operationally
simple protocol is selective for nitro-olefins and simply involves stirring substrate with an appropriate hydrogen-bond donor catalyst without any special precautions to exclude air or moisture. For each substrate examined, we have developed complementary protocols which respectively optimize yield and enantioselectivity. Our reactions scale well, and the products are valuable intermediates for further transformations, including for the preparation of enantioenriched vicinal amino-alcohols
- …
