| Catalytic asymmetric cascade reactions,being able to build up molecular complexity with high efficiency,are greatly desirable.These reactions essentially avoid additional time-consuming,costly workup,and isolation processes associated with the step-wise synthesis.Incorporating transition metal catalysis into organocatalytic asymmetric cascade reactions could make full use of their advantages and complement each other,allowing for many fundamentally new reactions.The research themes of this thesis have been focused on the development of catalytic cascade reactions enabled by transition metal/organo combined catalysis,aiming to realize the direct transformation of feedstock chemicals into high-value chiral products.Through the double chiral induction strategy,we have established an enantioselective carbonyl allylation of aldehydes with simple alkenes via a one-pot protocol consisting of a Pd-catalyzed allylic C-H borylation with bis(pinanediolato)diboron and a chiral Br(?)nsted acid catalyzed asymmetric allylborylation,delivering homoallylic alcohols in high yields and with excellent diastereo-and enantioselectivities.By means of rhodium/chiral phosphoric acid relay catalysis,we have established an efficient and general protocol for the synthesis of chiral tetrahydropyrans and tetrahydropyranones with high yields and high enantioselectivities.Two concise routes for the synthesis of key chiral building blocks to access herboxidiene and leucascandrolide A were also accomplished using the methodology.By integrating the palladium-catalyzed carbonylation and chiral Lewis base catalysis,we have developed a new method using benzyl bromides and CO as simple and inexpensive starting materials for the catalytic generation of Cl-ammonium enolates.This strategy allows asymmetric formal[1+1+4]and[1+1+2]annulation reactions of benzyl bromides,CO and N-tosylimines to give chiral dihydropyridones and ?-lactams in high optical purity. |
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