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DOI: 10.1055/s-0028-1087320
Air-Stable Iridium Catalyst in Asymmetric Allylic Substitution
Contributor(s):Mark Lautens, Jane PanteleevRuprecht-Karls-UniversitÄt Heidelberg, Germany
Iridium-Catalyzed Asymmetric Allylic Substitutions - Very High Regioselectivity and Air Stability with a Catalyst Derived from Dibenzo[a,e]cyclooctatetraene and a Phosphoramidite
Angew. Chem. Int. Ed. 2008, 47: 7652-7655
Publication History
Publication Date:
20 November 2008 (online)
Key words
asymmetric allylic substitution - iridium - phosphoramidite ligands
Significance
The authors report a new iridium catalyst system for the asymmetric allylic substitution reaction, furnishing improved chemoselectivity and comparable yields without the need for inert atmosphere. Additional mechanistic insight into precatalyst formation is reported based on ³¹P NMR experiments.
Comment
Although allylic substitution is a considerably refined transformation, the development of an air-stable iridium catalyst is noteworthy. The enhanced stability is achieved through the replacement of the commonly used cyclooctadiene ligand with dbcot and utilization of phosphoramidite ligands. The moderate scope of the reaction demonstrates that the new catalytic system is on par with the classic catalysts in terms of enantioselectivity. Through ³¹P NMR experiments, the authors postulate that the dbcot catalyst complexes the ligand more selectively, and that the C-H activation of the phosphoramidite ligand is not reversible. This irreversible catalyst formation may be responsible for the improved chemoselectivity.