Diastereoselective Pd(II)-Catalyzed sp3 C-H Arylation Followed by Ring Opening of Cyclopropanecarboxamides: Construction of anti β-Acyloxy Carboxamide Derivatives.
The diastereoselective Pd(OAc)2-catalyzed, bidentate ligand-directed sp3 C-H activation/arylation followed by ring opening of cyclopropanecarboxamides, which were assembled from cyclopropanecarbonyl chlorides and bidentate ligands (e.g., 8-aminoquinoline and 2-(methylthio)aniline), has been investigated. The treatment of various cyclopropanecarboxamides with excess amounts of aryl iodides in the presence of the Pd(OAc)2 catalyst, AgOAc and AcOH directly afforded the corresponding multiple β-C-H arylated open-chain carboxamides (anti β-acyloxy amides). This method has led to the construction of several anti β-acyloxy amides that possess vicinal stereocenters with a high degree of stereocontrol with the formation of a new C-O bond and three new C-C bonds. A plausible mechanism for the formation of multiple β-C-H arylated open-chain carboxamides from the Pd-catalyzed, bidentate ligand-directed β-C-H arylation and the ring opening of cyclopropanecarboxamides is proposed based on several control experiments. The observed diastereoselectivity and anti stereochemistry of the β-acyloxy amides were ascertained based on X-ray structural analysis of representative β-acyloxy amides.