In the present doctoral thesis, a series of novel chiral thiourea derivatives was firstly designed and synthesized, and their potential applications as organocatalysts were widely investigated in several important synthetic transformations, such as transfer hydrogenation of aldimines, biomimetic reduction of nitroolefins, cyanosilylation of ketones, and hydrophosphonylation of imines. Since the newly designed thiourea-based catalysts were generally inefficient for the promotion of reduction with trichlorosilane, various amino acids derived N-formamides were developed for the asymmetric reductions of ketimines using trichlorosilane as the hydrogen donor. The main results of this dissertation can be summarized as follows:
Chapter 3 describes our efforts in organocatalytic reductions:
3.1 challenging reported results from another group, we first reported that thiourea derivatives can catalyze transfer hydrogenation of aldimines through hydrogen bonding activation with Hantzsch ester as the hydrogen source.
3.2 describes a thiourea-catalyzed biomimetic reduction of nitroolefins with Hantzsch ester as the hydrogen donor, which may provide insights into the mechanism of redox reactions in biological systems.
3.5 a series of novel proline based N-formamides was firstly synthesized and characterized. Their catalytic efficiencies were investigated in asymmetric reductions of ketimines with trichlorosilane as the hydrogen source.
In chapter 4, we firstly demonstrated that the asymmetric addition of TMSCN to ketones can be promoted by one chiral module involving thiourea and anion moieties. In addition, n-BuLi was found to be an efficient agent for initiating this transformation.
In chapter 5, a one-pot three component addition of carbonyls, amines, and diethyl phosphite was found to proceed smoothly under neat conditions without catalysts and solvents. Moreover, the possibility of autocatalysis for the asymmetric addition of diethyl phosphite to imine was also investigated with kinetic and preparative methods.
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