نتایج جستجو برای: stereoselective
تعداد نتایج: 4707 فیلتر نتایج به سال:
Abstract In this paper, the synthesis of carbon skeleton cotylenin A aglycone is described. The key reactions, including an intramolecular aldol reaction, coupling and a ring-closing metathesis, allow for effective stereoselective access to aglycone. stereochemistry was confirmed by single-crystal X-ray crystallographic analyses related compounds.
Intramolecular nucleophilic substitution of a trifluoromethyl group to form a 1,2-diphosphole derivative followed by the sequential addition of an alkylating agent and a carbanion are the key steps in the stereoselective synthesis of novel ferrocenyl diphosphines for asymmetric catalysis.
An unexpected stereoselective anomeric substitution with carbamates promoted by HNTf2 is described here. Our experiments suggest that the observed diastereoselectivity is a result of thermodynamic equilibration of protonated N-acyl aminals.
An efficient and highly stereoselective synthesis of cytotoxic 8-epipuupehedione (1b) was achieved starting from natural (-)-drimenol (6). The key step to obtain stereoselectivity was the simultaneous demethylation and oxidation of the dihydrobenzopyran methoxy derivatives 10a and 10b.
Oxidative rearrangement of cyclic enol ethers leads to alpha-alkoxyesters. In the presence of a neighboring spiroether, this approach provides a stereoselective access to spiroketals. A modified proposal for the biosynthesis of acutumine is presented.
The first asymmetric synthesis of indole alkaloid (+)-subincanadine F was successfully accomplished with the uncommon 7-endo-trig stereoselective radical cyclization as the key step and its absolute configuration was thus assigned.
Asymmetric transfer hydrogenation of electron-deficient olefins is realized with nickel catalysts supported by strongly σ-donating bisphosphines. Deuterium labeling experiments point to a reaction sequence of formate decarboxylation, asymmetric hydride insertion and non-stereoselective protonation of resulting nickel enolates.
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