Enantioselective conjugate addition of phenylboronic acid to enones catalysed by a chiral tropos/atropos rhodium complex at the coalescence temperature

2005 ◽  
pp. 5281 ◽  
Author(s):  
Chiara Monti ◽  
Cesare Gennari ◽  
Umberto Piarulli
Keyword(s):  
Phenylboronic Acid ◽  
Conjugate Addition ◽  
Rhodium Complex ◽  
Coalescence Temperature

scholarly journals Rhodium-catalyzed asymmetric reactions with a dynamic library of chiral tropos phosphorus ligands

2006 ◽  
Vol 78 (2) ◽  
pp. 303-310 ◽  
Author(s):  
Cesare Gennari ◽  
Chiara Monti ◽  
Umberto Piarulli
Keyword(s):  
Amino Acids ◽  
Secondary Amine ◽  
Phenylboronic Acid ◽  
Conjugate Addition ◽  
Asymmetric Reactions ◽  
Temperature Dependent ◽  
Phosphorus Ligands ◽  
Cyclic Enones ◽  
Dynamic Library ◽  
Coalescence Temperature

Nineteen chiral tropos phosphorus ligands, based on a flexible (tropos) biphenol unit and a chiral P-bound alcohol (11 phosphites) or secondary amine (8 phosphoramidites), were screened, individually and as a combination of two, in various Rh-catalyzed asymmetric reactions. In the Rh-catalyzed asymmetric conjugate addition of phenylboronic acid to cyclic enones, enantiomeric excesses (ee's) up to 95 % were obtained with a 1:1 mixture of a phosphite [derived from (1R,2S)-2-(1-methyl-1-phenylethyl)cyclohexanol] and a phosphoramidite [derived from (S,S)-2,5-diphenylpyrrolidine]. In the mixed Rh precatalyst, which was characterized via 31P-NMR, the biphenol-derived phosphite is free to rotate (tropos) while the biphenol-derived phosphoramidite shows a temperature-dependent tropos/atropos behavior (coalescence temperature = 310 K). The ligands were also screened in the hydrogenation of dehydro-α-amino acids and dehydro-β-amino acids. Ee's up to 98% were obtained for the dehydro-α-amino acids, using the combination of a phosphite [derived from (1R,2S)-2-phenyl-1-cyclohexanol] and a phosphoramidite [derived from (S,S)-bis(α-methylbenzyl)amine]. The reaction was optimized by lowering the phosphite/phosphoramidite ratio to 0.25:1.75 with a resulting improvement of the product ee.

A visible-light-activated rhodium complex in enantioselective conjugate addition of α-amino radicals with Michael acceptors

2017 ◽  
Vol 53 (54) ◽  
pp. 7665-7668 ◽  
Author(s):  
Shao-Xia Lin ◽  
Gui-Jun Sun ◽  
Qiang Kang
Keyword(s):  
Visible Light ◽  
Conjugate Addition ◽  
Rhodium Complex ◽  
Michael Acceptors

An efficient enantioselective conjugate addition of photogenerated α-amino radicals to Michael acceptors catalyzed by a single and newly prepared chiral-at-metal rhodium complex was established.

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