1,720,972 research outputs found
Synthesis of N-heterocyclic compounds via ene-yne metathesis reactions
No full textPropargylamino and allylamino derivatives of cyclohexene and norbornene were subjected to tandem metathesis reactions with first and second generation Grubbs' catalysts 1 and 2. Results show that the method is compatible with suitably protected nitrogen-containing compounds. Cyclohexenes gave intriguing results in terms of the possibility to perform ring rearrangement metathesis (RRM) reactions, showing a difference with the analogous allyl and propargyl ether substrates. © 2007 Elsevier Ltd. All rights reserved
Corrigendum to "Synthesis of N-heterocylic compounds via ene-yne metathesis reactions" [Tetrahedron 64(1) (2008) 204-218] (DOI:10.1016/j.tet.2007.10.076)
No full textSynthesis of cyclic and macrocyclic ethers using metathesis reactions of alkenes and alkynes
No full textThe metathesis transformations of cyclohexanes and cyclohexenes bearing allylic and/or propargylic ether substituents has been investigated. A range of products containing fused 6,8-bicyclic ring systems resulting from alkene and/or enyne metatheses were obtained using first and second generation, well defined alkylidene ruthenium catalysts. However, the unstrained cyclohexene unit did not participate in any of these metathesis processes, even though doing so would have led to a thermodynamically more stable product. This contrasts with previous results on similar compounds and on the corresponding amino-substituted cyclohexenes. The synthesis of dienes and dihydrofurans by metathesis processes involving the side chains of suitable cyclohexene ethers is also reported. When the unstrained cyclohexene unit was replaced by a norbornene group, the strained alkene did participate in a cascade of alkene and enyne metatheses. This chemistry was extended to alkyne metatheses of cyclohexene and norbornene esters, leading to 6,12-fused cycloalkynes which would subsequently undergo further enyne and/or alkene metatheses. This culminated in the development of the first one-pot metathesis process in which alkyne, enyne and alkene metathesis reactions initiated by two different catalysts all occur sequentially to form a 5,12-fused bicyclic diene product. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007
Alkene and enyne metathesis reactions on allylic and propargylic amines
No full textTreatment of cis-4,5-diaminocyclohexene derivatives bearing allyl or propargyl groups on the nitrogen atoms, with first or second generation Grubbs metathesis catalysts, results in initiation of metathesis cascades which include ring-opening of the unstrained cyclohexene ring. This contrasts with the previous work on the analogous cyclohexene ethers where metathesis reactions occurred exclusively between the side-chains and no ring-opening of the cyclohexene unit was observed. © 2007 Elsevier Ltd. All rights reserved
Ene-yne metathesis of polyunsaturated norbornene derivatives
Full text linkNorbornene derivatives bearing endo-substituents in the 5- and 6-positions were studied as substrates for ene-yne metathesis cascades. Substrates which contained an internal alkyne and a terminal alkene or alkyne in each sidechain were found to undergo a metathesis cascade leading to pentacyclic bis-dienes and bis-trienes. Attempts to extend the chemistry further to sidechains containing two internal alkynes or two internal alkynes and a terminal alkene were not successful with the first generation Grubbs' catalyst. However, the substrate containing two internal alkynes did react with the second generation Grubbs' catalyst to give a tetra-diene containing product. Ruthenium based metathesis initiators have been used to convert readily available norbornene derivatives bearing polyunsaturated sidechains into highly functionalised polycyclic compounds. © 2004 Elsevier Ltd. All rights reserved
Diastereoselectivity in the synthesis of bicyclic titanacyclopentenes from chiral 6-hepten-1-ynes
No full text
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
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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