750 research outputs found
How cinchona alkaloid-derived primary amines control asymmetric electrophilic fluorination of cyclic ketones.
The origin of selectivity in the α-fluorination of cyclic ketones catalyzed by cinchona alkaloid-derived primary amines is determined with density functional calculations. The chair preference of a seven-membered ring at the fluorine transfer transition state is key in determining the sense and level of enantiofacial selectivity
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Boron carboxylate catalysis of homoallylboration.
Boron tris(trifluoroacetate) is identified as the first effective catalyst for the homoallyl- and homocrotylboration of aldehydes by cyclopropylcarbinylboronates. NMR spectroscopic studies and theoretical calculations of key intermediates and transition states both suggest that a ligand-exchange mechanism, akin to our previously reported PhBCl2-promoted homoallylations, is operative. Our experimental and theoretical results also suggest that the catalytic activity of boron tris(trifluoroacetate) might originate from more facile catalytic turnover of the trifluoroacetate ligands (in agreement with DFT calculations) or from a lower propensity for formation of off-pathway reservoir intermediates (as observed by (1)H NMR). This work shows that carboxylates are viable catalytic ligands for homoallyl- and homocrotylations of carbonyl compounds and opens the door to the development of catalytic asymmetric versions of this transformation
Diagnostic yield at bronchoscopy samplying in bronchial carcinoma
published_or_final_versio
The relationship between sputum microbial load and inflammatory indices in bronchiectasis
published_or_final_versio
Presenting features of bronchial adenocarcinoma in Chinese patients
published_or_final_versio
Sputum elastase activity correlates with clinical parameters in steady state bronchiectasis
Conference Theme: Challenges to specialists in the 21st centurypublished_or_final_versio
Bronchoalveolar lavage is a safe and effective sampling modality for the diagnosis bronchial carcinoma
Conference Theme: Challenges to specialists in the 21st centurypublished_or_final_versio
Preliminary results of prevalence study of obstructive sleep apnoea in middle-aged Chinese in Hong Kong
published_or_final_versio
Ciliary central microtubular orientation in stable bronchiectasis
published_or_final_versio
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