Construction And Biological Activity Study Of Triaryl-substituted Silicon Chiral Functional Molecule

Silicon is the second most abundant element in the crust.Although natural appearance of silicon element in living systems are uncommon,incorporation of this element to organic molecules have led to impressive applications as medicines and agrochemicals.Indeed,various molecules containing silicon element have been commercialized as pesticides,and more candidates are being developed at various stages.Outside of biological applications,silicon-containing organic molecules have been found applications in many areas such as materials and catalysis.It has now been well recognized that replacing carbon with silicon atoms in organic molecules can lead to improved and/or alternative functions.On the other side,methods for synthesis of silicon-containing moleucles remain much unmature.The synthetic challenge further increases when silicon-stereogenic centre are to be constructed.The Si-C bond is longer than the corresponding C-C bond,making it difficult to form well-organized transition states.In addition,silicon can form more than four covalent bonds and thus lead to racemization of the stereogenic centre.To date,the impressive yet still limited success for asymmetric synthesis of silicon-stereogenic centre-containing molecules are exclusively achieved via transition metal-catalyzed reactions.These methods use chiral ligand/metal complexes-catalyzed processes to form new carbon-silicon bond or selectively functionalize one of the two pro-chiral groups attached to silicon atom.Enzymes and organic catalysts have found enormous applications in building carbon chiral centers.Unfortunately,in the area of silicon-stereogenic centre synthesis,few reactions are developed using enzymes or organic catalysts.We believe it is worth to explore the potentials of organic catalysis to construct silicon atom chiral centers.Here we disclose an N-heterocyclic carbene(NHC)-catalyzed desymmetrization reaction for access to tetrasubstituted silicon-stereogenic silanes.The overall catalytic process converts one of the two aldehyde moieties of the Si-containing dialdehyde substrate to a carboxylic ester group,leading to tetrasubstituted silicon-stereogenic silanes with high optical purities.Our experimental observations and DFT calculations on key reaction steps suggest that the addition steps and formation of Breslow intermediate between the NHC catalyst and the dialdehyde substate did not provide sufficient differentiations.Instead,stereo-determining and desymmtrization were realized during the formation of acylazuolium intermediate.Our transition metal-free catalytic reaction conditions are mild with good functional group tolerance.The optically enriched silicon-stereogenic products from our method can be readily transformed to a diverse set of molecules with the silicon stereogenic center remaining intact.The preliminary screening of pesticide activity showed that these chiral silanes had certain inhibitory activity against Xanthomonas axonopodis pv.Citri and Phytophthora capsici.