Palladium-Catalyzed Coupling of Allylic Acetates with Aryl- and Vinylstannanes
L. Del Valle, J. K. Stille and L. S. Hegedus*
*Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
L. Del Valle, J. K. Stille, L. S. Hegedus, J. Org. Chem, 1990, 55, 3019-3023.
DOI: 10.1021/jo00297a014
Abstract
The palladium-catalyzed reaction of allyl acetates with aryl- and vinyltin reagents gave good yields of cross-coupled products. The reaction was mild and tolerant of functionality (-CO2R, -OH, -OSiR3, -OMe) in the tin reagent. Inversion of stereochemistry at the acetate center was observed, with retention of the geometry of the olefin of the allyl group and with exclusive coupling at the primary position. Retention of geometry of the olefin in the vinyltin reagents was also observed.
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proposed mechanism
Details
The document details the palladium-catalyzed coupling of allylic acetates with aryl and vinylstannanes, conducted by L. Del Valle, J. K. Stille, and L. S. Hegedus at Colorado State University. This reaction, which is mild and tolerant of various functional groups (CO2R, OH, OSiR3, OMe), yields cross-coupled products efficiently. The standard conditions involve using DMF as a solvent, lithium chloride to assist transmetalation, and Pd(dba)2 as the catalyst, without added phosphine. The reaction retains the geometry of the olefin in both the allylic and vinyltin reagents and shows exclusive coupling at the primary position with inversion of stereochemistry at the acetate center. Secondary and tertiary allylic acetates undergo complete allylic transposition, resulting in exclusive coupling at the primary position. The study highlights the reaction's potential in organic synthesis, exemplified by the production of a precursor to the antibiotic grifolin in excellent yield. The proposed mechanism involves oxidative addition of the allylic acetate to palladium(0), transmetalation from tin to palladium, and reductive elimination to produce the coupling product. The findings provide valuable insights into the scope and limitations of this coupling process, demonstrating its utility in forming carbon-carbon bonds in functionalized organic compounds.
Key Words
Stille Coupling, Palladium Catalysis, Allyl Acetates, Aryltin Reagents, Vinyltin Reagents, Allyls, Arenes, Vinyls
ID: J42-Y1990-090
