930 research outputs found
Carbohydrates as enantioinduction components in stereoselective catalysis
Carbohydrate derivatives are readily available chiral molecules, yet they are infrequently employed as enantioinduction components in stereoselective catalysis. In this review, synthetic approaches to carbohydrate-based ligands and catalysts are outlined, along with example applications in enantioselective catalysis. A wide range of carbohydrate-based functionality is covered, and key trends and future opportunities are identified
Pseudo-enantiomeric carbohydrate-based N-heterocyclic carbenes as promising chiral ligands for enantiotopic discrimination
Culture, Environment and Technology: Preliminary Results of an Archaeological Study in Kenya
During 1975-6, extensive data were collected on late prehistoric cultures in the Central Rift Valley, Kenya, and adjoining regions. A stratified archeological survey was conducted in an area of about 22,000 km2 centering on the Naivasha and Nakuru lake basins. The area was divided into 20 units (strata) defined by elevation and precipitation, and approximately 5% of each unit was targeted for survey. Although the study was aimed primarily at later stone age cultures, no stage of prehistory was excluded from the survey, and the data also reflect earlier stone age and iron age cultures. Just over 100 sites were located, and test excavations were conducted in 9 of them. A preliminary analysis of the survey materials and excavated data provides interesting insights on settlement behavior, technology, and culture history
Stereoselective synthesis of glycosides using (salen)Co catalysts as promoters
The use of (salen)Co catalysts as a new class of bench-stable stereoselective glycosylation promoters of trichloroacetimidate glycosyl donors at room temperature is described.</p
Modular access to substituted azocanes via a rhodium-catalyzed cycloaddition-fragmentation strategy
A short entry to
substituted azocanes by a Rh-catalyzed cycloadditionâfragmentation
process is described. Specifically, exposure of diverse <i>N</i>-cyclopropylacrylamides to phosphine-ligated cationic RhÂ(I) catalyst
systems under a CO atmosphere enables the directed generation of rhodacyclopentanone
intermediates. Subsequent insertion of the alkene component is followed
by fragmentation to give the heterocyclic target. Stereochemical studies
show, for the first time, that alkene insertion into rhodacyclopentanones
can be reversible
Electrophilic Aminating Agents in Total Synthesis
Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful CâN bondâforming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis
Selective Carbon-Carbon Bond Cleavage of Cyclopropylamine Derivatives.
This review summarizes synthetic developments reported from 1987 to 2019 that exploit C-C single bond cleavage of cyclopropylamine-based systems. The synthetic and mechanistic aspects of key methodologies are highlighted, and examples where aminocyclopropanes are exploited as key intermediates in multistep synthesis are also discussed. The review encompasses cases where aminocyclopropanes participate in polar reactions, pericyclic processes, radical-based reactions, and C-C bond activations
Recent Methodologies That Exploit C-C Single-Bond Cleavage of Strained Ring Systems by Transition Metal Complexes
Rhodacyclopentanones as Linchpins for the Atom Economical Assembly of Diverse Polyheterocycles
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