1,720,962 research outputs found
Amino-sugar modular ligands-useful cores for the formation of asymmetric copper 1,4-addition catalysts
No full textModular phosphine ligands, synthesized rapidly from com. N-acetylglucosamine, are very effective in copper(I)-catalyzed 1,4-addns. of ZnR2 to linear aliph. enones (87-95% ee)
Carbohydrates as building blocks of privileged ligands for multiphasic asymmetric catalysis
No full textCarbohydrates as building blocks of privileged ligands
No full text“Privileged ligands” are chiral auxiliaries of wide applicability in asymmetric catalysis. In the previous decades, their effective three-dimensional structures have often been reproduced by using building blocks from a “chiral pool”, such as the carbohydrates. This strategy has provided unique ligand moieties which combine the performance of “privileged ligands” with increased flexibility and accessibility. This review gives an overviewof the research within this field, giving emphasis to the best results obtained with each ligand type
Carbohydrates as building blocks of "privileged" ligands for multiphasic asymmetric catalysis
No full textA convenient route from simple sugars to new chiral bis(phosphinoesters) for asymmetric catalysis
No full textReadily available chiral bis(phosphinoesters) based on d-glucose, d-mannose and d-galactose have been prepared in only two steps and in large scale starting from inexpensive commercial precursors. Their Pd complexes catalyze the asymmetric desymmetrization of meso-cyclopent-4-ene-1,3-diol biscarbamate in ee’s up to 82%
Carbohydrates as building blocks of privileged ligands for multiphasic asymmetric catalysis
No full textTo combine the high chem. performance of asym. catalysis with the increasing need fo sustainability, a strategy is presented that involves the straightforward prepn. of "Trost"-like ligands suitable for application in multiphasic homogeneous catalysis. Ligands with coordinating functions (phosphinoamide-phosphinoester groups) as well as phase tags introduced on a D-glucose scaffold were prepd. and then examd. in the Pd-catalyzed asym. desymmetrization of meso-2-cyclopenten-1,4-diol biscarbamate. In line with our assumption, the performance of the catlyst system under traditional conditions is as high as that of the original Trost ligand, derived from trans-cyclohexanediamine, giving enantioselectivities of 98 % ee. Moreover, promising results were obsd. under multiphasic homogeneous conditions
New P,N,N’,P’ ligands based on carbohydrates for highly enantioselective Pd-catalysed allylic substitution
No full textBis(phosphinoamides) based on sugars for highly enantioselective allylic substitution: inversion of stereocontrol by switching from glucose to mannose
No full textNew chiral bis(phosphinoamides) based on glucose 1G and mannose 1M have been prepared. Their Pd complexes catalyze the asymmetric desymmetrization of meso-cyclopenten-2-ene-1,4-diol biscarbamate in high ee’s (up to 97%). Glucose and mannose moieties selectively promote formation of the opposite enantiomers, as a consequence of inverted steric motifs around the metal center
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
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