104,633 research outputs found
Cyclopropyl building blocks for organic synthesis, 58 - A new short access to amino acids incorporating an aminocyclopropyl moiety from N,N-dibenzylcarboxamides
No full textOur recently reported titanium-mediated transformation of N,N-dialkylcarboxamides to cyclopropylamines has been applied to N,N-dibenzyl-2-benzyloxyacetamide using a variety of alkylmagnesium bromides to yield 1-(benzyloxymethyl)-1-(dibenzylamino)cyclopropane (15a, 48%) and 2-substituted analogs 15b-f (33-48%). These have been transformed in just a few steps into N-Boc-protected methyl esters of 1-ami-nocyclopropanecarboxylic acid (1, 29% overall), coronamic acid (2, 35%) and norcoronamic acid (21%), 2,3-methanoglutamic acid (21g, 19%) and 2,3-methanoornithine (21I, 12%). Similarly, the corresponding derivatives of 3,4-methano-gamma-aminobutyric acid (26, 23%) and 4-spirocyclopropane-gamma-butyrolactam (32, 44%) have been synthesized
Cyclopropyl building blocks for organic synthesis, 58 - A new short access to amino acids incorporating an aminocyclopropyl moiety from N,N-dibenzylcarboxamides
No full textOur recently reported titanium-mediated transformation of N,N-dialkylcarboxamides to cyclopropylamines has been applied to N,N-dibenzyl-2-benzyloxyacetamide using a variety of alkylmagnesium bromides to yield 1-(benzyloxymethyl)-1-(dibenzylamino)cyclopropane (15a, 48%) and 2-substituted analogs 15b-f (33-48%). These have been transformed in just a few steps into N-Boc-protected methyl esters of 1-ami-nocyclopropanecarboxylic acid (1, 29% overall), coronamic acid (2, 35%) and norcoronamic acid (21%), 2,3-methanoglutamic acid (21g, 19%) and 2,3-methanoornithine (21I, 12%). Similarly, the corresponding derivatives of 3,4-methano-gamma-aminobutyric acid (26, 23%) and 4-spirocyclopropane-gamma-butyrolactam (32, 44%) have been synthesized
Easy access to (n+3)-dimethylamino-1-ethenylbicyclo[n.1.0]alkanes and their facile conversion to ring-annelated cyclopentadienes
No full textAminocyclopropanation of 1-ethenylcycloalkenes 2a-d with N,N-dibenzyl- and N,N-dimethylformamide, respectively, by treatment with cyclohexylmagnesium bromide in the presence of methyltitanium triisopropoxide yielded the exo-(n+3)-N,N-dimethylamino-1-ethenylbicyclo[n.1.0]alkanes 3a-d (58-72%). Compounds 7b-d could be transformed by thermal vinylcyclopropane to cyclopentene rearrangement to the corresponding exo-4-dimethyl-aminobicyclo[n.3.0]alk-1-enes 7b-d (84-90%). Elimination of the dimethylamino group led to the cyclopentadienes 11b-d and 12b-d (72-82%). The 5-dimethylamino-1-ethenylbicyclo[2.1.0]pentane did not undergo the typical vinylcyclopropane rearrangement, but ring-opening at the bridgehead-bridgehead bond to form 1-ethenyl-2-dimethylaminocyclopentene 8
Easy access to (n+3)-dimethylamino-1-ethenylbicyclo[n.1.0]alkanes and their facile conversion to ring-annelated cyclopentadienes
No full textAminocyclopropanation of 1-ethenylcycloalkenes 2a-d with N,N-dibenzyl- and N,N-dimethylformamide, respectively, by treatment with cyclohexylmagnesium bromide in the presence of methyltitanium triisopropoxide yielded the exo-(n+3)-N,N-dimethylamino-1-ethenylbicyclo[n.1.0]alkanes 3a-d (58-72%). Compounds 7b-d could be transformed by thermal vinylcyclopropane to cyclopentene rearrangement to the corresponding exo-4-dimethyl-aminobicyclo[n.3.0]alk-1-enes 7b-d (84-90%). Elimination of the dimethylamino group led to the cyclopentadienes 11b-d and 12b-d (72-82%). The 5-dimethylamino-1-ethenylbicyclo[2.1.0]pentane did not undergo the typical vinylcyclopropane rearrangement, but ring-opening at the bridgehead-bridgehead bond to form 1-ethenyl-2-dimethylaminocyclopentene 8
ChemInform Abstract: A New Versatile Reagent for the Synthesis of Cyclopropylamines Including 4-Azaspiro(2.n)alkanes and Bicyclo(n.1.0)alkylamines.
No full textPrimary 1-arylcyclopropylamines from aryl cyanides with diethylzinc and titanium alkoxides
No full text[GRAPHICS] 1-Aryl-substituted primary cyclopropylamines are conveniently prepared from aromatic nitriles and diethylzinc. The yields range from 40 to 56% for donor-substituted (five examples) to 62-82% for non- and acceptor-substituted substrates (nine examples)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
No full textWe 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
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
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