Regio- and Enantioselective Palladium-Catalyzed (4 + 2) Silacycloaddition of Unsymmetrical Internal Alkynes with Racemic Benzosilacyclobutenes

Silicon-stereogenic architectures are valuable in organosilicon
chemistry and medicinal chemistry, but their enantioselective synthesis
via silicon-centered chirality transfer remains a challenge. In contrast
to well-studied chirality-at-carbon chemistry, the construction of
silicon-stereogenic centers has been considered as a challenging topic
due to its limited synthetic strategy. Here, we realized a kinetic
resolution process to establish a palladium-catalyzed enantioselective
ring-expansion-type (4 + 2) silacycloaddition reaction of racemic
benzosilacyclobutenes with unsymmetrical internal alkynes via selective
Si–C(sp3) bond cleavage. By employing a chiral TADDOL-derived
phosphoramidite ligand, we achieved the kinetically controlled catalytic
asymmetric construction of silicon-stereogenic benzo[c]silin derivatives
with good enantioselectivity. The catalytic system features mild conditions,
high chemoselectivity, a broad substrate scope, and good functional
group tolerance, demonstrating broad applicability to unsymmetrical
alkynes bearing terminal ketone or ester groups. Furthermore, the
kinetic studies of racemic substrates corroborate the versatility
and applicability of this strategy, offering a robust strategy called
the kinetic resolution of racemic substrate in this work to access
structurally diverse silicon-stereogenic organosilicon compounds.