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DOI: 10.1055/s-2008-1042691
Catalytic Nucleophilic Ring Closure ofπ-Allylpalladium Intermediates
Contributor(s):Mark Lautens, Praew ThansandoteKyoto University, Japan
Palladium-Catalyzed Synthesis of Spiro[2.4]heptanes: Ligand-Dependent Position Control in the Nucleophilic Attack to a π-Allylpalladium Intermediate
J. Am. Chem. Soc. 2007, 129: 14866-14867
Publication History
Publication Date:
21 February 2008 (online)
Key words
palladium - allylic alkylation - cyclopropanation - spiro[2.4]heptanes
Significance
The authors describe the development of a palladium-catalyzed intermolecular cycloaddition that involves a nucleophliic ring closure to the central carbon of a π-allylpalladium intermediate. Spiro[2,4]heptanes are obtained in good yields and moderate diastereoselectivities using small phosphite ligands. If bulky phosphine ligands are used, a selective [4+2] cycloaddition occurs, leading to exo-methylene cyclohexane products.
Comment
The influence of the size of the ligand on product distribution may suggest that the π-allylpalladium intermediate Pd(π-allyl)L 2 leads to ring closure via central carbon attack, while the Pd(π-allyl)L 1 intermediate leads to cyclohexane formation via terminal attack by the nucleophile. Though moderate diastereoselectivity is shown, this transformation could be widely applicable if an asymmetric variant is developed.