Abstract
A regioselective and enantioselective palladium-catalyzed relay Heck alkenylation of alkenylbenzene derivatives to construct remote stereocenters is disclosed. Various β-substituted styrenes were readily obtained in moderate yields with good to excellent levels of enantioselectivity. This strategy provides rapid access to enantioenriched δ, ε, ζ, and η-alkenyl aryl compounds from simple starting materials. Mechanistic studies suggest that termination of the relay reaction is controlled by affinity of the arene for the Pd complex during migration.
Highlights
The migration of a metal through an alkyl chain via iterative bhydride elimination/migratory insertion processes, o en termed chain walking offers the opportunity to effectively functionalize multiple sites on a substrate.[1]
The formation of the aldehyde facilitates this in two key regards: (1) the penultimate proposed intermediate (C) is thermodynamically stabilized according to computational studies and (2) the resulting aldehyde does not participate in migratory insertion events making the process irreversible.[6]
The mass balance was a mixture of the undesired migratory insertion product and other alkene isomers 4
Summary
The migration of a metal through an alkyl chain via iterative bhydride elimination/migratory insertion processes, o en termed chain walking (or running) offers the opportunity to effectively functionalize multiple sites on a substrate.[1]. Coupled together, expanding the scope of chain walking events within a Heck platform will likely require similar tactics
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