A new approach for the fully chemoselective α-arylation of amides is presented. By means of electrophilic amide activation, aryl groups can be regioselectively introduced α- to amides, even in the presence of esters and alkyl ketones. Mechanistic studies reveal key reaction intermediates and emphasize a remarkably subtle base effect in this transformation.
Here we describe
an asymmetric [3,3]-sigmatropic rearrangement
of aryl iodanes that enables the enantioselective α-arylation
of chiral 2-oxazolines, thereby producing valuable chiral α-aryl
carbonyl compounds. The success of this protocol hinges on the selective
assembly of aryl iodanes with 2-oxazolines and the smooth deprotonation
of the in situ-generated iodonium–imine species. The nearly
neutral and mild conditions of the reaction allow it to tolerate a
wide variety of functional groups. Moreover, the remaining iodine
atom in the products not only provides a versatile platform for further
elaboration of such molecules but also supplies the asymmetric hypervalent
iodine chemistry with a new class of chiral scaffolds.
The direct functionalization of C-H bonds is an attractive strategy in organic synthesis. Although several advances have been made in this area, the selective activation of inert sp(3) C-H bonds remains a daunting challenge. Recently, a new type of sp(3) C-H activation mode through internal hydride transfer has demonstrated the potential to activate remote sp(3) C-H linkages in an atom-economic manner. This Minireview attempts to classify recent advances in this area including the transition to non-activated sp(3) C-H bonds and asymmetric hydride transfers.
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