Stereoconvergent Arylations and Alkenylations of Unactivated Alkyl Electrophiles: Catalytic Enantioselective Synthesis of Secondary Sulfonamides and Sulfones

The
development of efficient methods for the generation of enantioenriched
sulfonamides and sulfones is an important objective for fields such
as organic synthesis and medicinal chemistry; however, there have
been relatively few reports of direct catalytic asymmetric approaches
to controlling the stereochemistry of the sulfur-bearing carbon of
such targets. In this report, we describe nickel-catalyzed stereoconvergent
Negishi arylations and alkenylations of racemic α-bromosulfonamides
and -sulfones that furnish the desired cross-coupling product in very
good ee and yield for an array of reaction partners. Mechanistic studies
are consistent with the generation of a radical intermediate that
has a sufficient lifetime to diffuse out of the solvent cage and to
cyclize onto a pendant olefin.