| The reaction system of free radical addition initiated by triethylborane to aldimine compounds has developed quickly since the 1990s.When compared to the free radical addition reaction of chiral auxiliary groups to imine compounds,the research progress of asymmetric catalytic free radical addition reaction is far from ideal.The prior art methods achieve asymmetric induction by interaction of a chiral Lewis acid or a chiral Br?nsted acid with a substrate,and a large amount of chiral reagent to obtain a better enantioselectivity.It is evident that existing methods have achieved stereochemical control at the equivalent level with the possibility of developing asymmetric catalysis.However,there is still a lack of practicality,and further improvement of catalytic efficiency is urgently needed.Based on previous studies,we have further developed the free radical addition reaction of asymmetrically catalyzed imine compounds to synthesize our three years of research results.Our research results are as follows:1.We developed and established a class of Lewis acid triflate as Lewis acid catalyst,Hans ester as a dihydrogen atom donor,and free radical addition initiated by triethylborane to oxazolinone and a reaction system of an aldimine-like compound.In this reaction system,Fe2+was used as lewis acid for the first time,and the reaction conditions were screened under the condition of catalytic capacity.Hantzsch ester was used as hydrogen donor for the first time.Similarly,we found that substrates with strong electron-withdrawing groups are more reactive in this reaction system.2.Our results indicate that the combination of Fe2+Lewis acid and dihydropyridine hydrogen donor may be an effective method to develop chiral lewis acid to catalyzed free radical in addition to aldimine.Since N-N in our aldimine addition products can be cleaved by known methods,this method may be applied to the synthesis of chiral amines such asα-amino acids,thereby providing a theoretical basis for the subsequent synthesis of such compounds. |
