ABSTRACT
Although palladium-catalyzed asymmetric C-H functionalization and Heck reactions represents one of the most important synthetic strategies for the construction of quaternary stereocenters, developing the enantioselective version of PdII -catalyzed carbopalladation-initiated cascade reactions still remains a formidable challenge. Herein, an unprecedent enantioselective [3+2] annulation of oxime ethers and alkynes has been developed, providing both spiro and nonspiro indenes bearing all-carbon quaternary stereocenters in good yields (up to 98 %) with excellent enantioselectivities (up to >99 % ee). This annulation is accomplished by merging the PdII -catalyzed atroposelective C-H activation/double carbopalladation and the transient axial-to-central chirality transfer process, constituting the first successful example of catalytic chirality transfer strategy involving axially chiral styrene intermediate.
ABSTRACT
Although asymmetric C-H functionalization has been available for the synthesis of structurally diverse molecules, catalytic dynamic kinetic resolution (DKR) approaches to change racemic stereogenic axes remain synthetic challenges in this field. Here, a concise palladium-catalyzed DKR was combined with C-H functionalization involving olefination and alkynylation for the highly efficient synthesis of non-biaryl-atropisomer-type (NBA) axially chiral oragnosilanes. The chemistry proceeded through two different and distinct DKR: first, an atroposelective C-H olefination or alkynylation produced axially chiral vinylsilanes or alkynylsilanes as a new family of non-biaryl atropisomers (NBA), and second, the extension of this DKR strategy to twofold o,o'-C-H functionalization led to the multifunctional axially chiral organosilicon compounds with up to >99 % ee.
