Abstract
Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry. However, catalytic asymmetric hydrosilylation of activated alkenes and internal alkenes has proven elusive, due to competing reduction of carbon-carbon double bond or isomerization processes. Herein, we report a highly enantioselective Si-C coupling by hydrosilylation of carbonyl-activated alkenes using a palladium catalyst with a chiral TADDOL-derived phosphoramidite ligand, which inhibits O-hydrosilylation/olefin reduction. The stereospecific Si-C coupling/hydrosilylation of maleimides affords a series of silyl succinimides with up to 99% yield, >99:1 diastereoselectivity and >99:1 enantioselectivity. The high degree of stereoselectivity exerts remote control of axial chirality, leading to functionalized, axially chiral succinimides which are versatile building blocks. The product utility is highlighted by the enantioselective construction of N-heterocycles bearing up to three stereocenters.
Highlights
Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry
It was found that only chiral TADDOL-derived phosphoramidites bearing aromatic bulky groups could give low to moderate yields of desired silyl product 3a in the palladium-catalysed hydrosilylation of N-phenylmaleimide (Table 1 and Supplementary Table 1, TADDOL = 1,1,4,4-tetra-aryl-2,3-O-isopropylidene-Lthreitol)
To clarify the stereospecific Si–C coupling process by palladiumcatalysed hydrosilylation of maleimides, DFT calculations revealed that high chemo- and enantioselectivity originates from the aromatic interaction and steric repulsion caused by chiral TADDOL-derived phosphoramidite acting with the Pd–Si intermediate’s aryl unit, in turn coordinated with carbon–carbon double bond of maleimide
Summary
Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry. We reported a highly enantioselective Si–C coupling hydrosilylation of carbonyl-activated alkenes using palladium catalysis with chiral TADDOL-derived phosphoramidite ligand, which inhibited previously common O-hydrosilylation/reduction of carbon–carbon double bond This was proved in the enantioselective hydrosilylation in maleimides as well as the remote control of axial chirality of N-arylmaleimides via a single-step transformation. Hydrosilylation of unsaturated carbon–carbon bonds with hydrosilanes ranks one of the most fundamental reactions in industrial chemical production[8,9,10,11,12,13,14], such as the production of coupling silane and silicone rubber[15] Recently it has become a very important process to access synthetically useful organosilicon compounds and chiral organosilanes[16,17,18] that are useful in asymmetric catalysis, functional materials, and can be employed as silicon-containing drug candidates. If a chiral ligand bearing a bulky and cavity-like group as well as displaying suitable secondary interactions could be beneficial to the formation of a proton shuttle for subsequent Si–C coupling hydrosilylation, a highly enantioselective hydrosilylation of EWG-activated alkenes (EWG: electron-withdrawing group) would be achieved
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