Study On Asymmetric Photochemical Synthesis Of 2,3-Dihydropyrroles

Dihydropyrroleanditsderivativesareimportantnitrogen-containing heterocycles in pharmaceuticals,bioactive natural products,pesticides,materials,dyes and so on.Its synthesis has attracted the attention of researchers,there are few reports on the synthesis of dihydropyrrole by asymmetric photochemical synthesis.Here,the asymmetric photochemical method was used for the synthesizing the dihydropyrroles with the 1,4-dihydropyridine as the raw material.The results will provide a synthesis method with higher stereoselectivity.The study on the asymmetric photochemical synthesis of 2,3-dihydropyrrole from 1,4-dihydropyridine can provide theoretical and experimental basis for the application of asymmetric photochemical synthesis methods in heterocycles.The studies on the synthesis of 1,4-dihydropyridines were focused on the target compoundsof1,4-dihydropyridinederivatives?withsymmetricallyand asymmetrically substituted?and 1,4-dihydropyridine with a chiral auxiliary.Based on the classical Hantzsch principle,the one-pot synthesis was used to obtain the title compound with higher efficiency and convenience.The symmetrically and asymmetrically substituted 1,4-dihydropyridines were prepared by the reaction of aryl aldehyde,3-aminocrotonate esters and acetoacetate esters.The 1,4-dihydropyridine with a chiral auxiliary were prepared by the reaction of aryl aldehyde,methyl3-aminocrotonate and chiral auxiliary acetoacetate.The results on the chiral resolution of 1,4-dihydropyridines can provide a higher chiral environment for the photochemical synthesis of 2,3-dihydropyrroles.The studies on the asymmetric photochemical synthesis of 2,3-dihydropyrrole were focused on the photochemical reaction of 1,4-dihydropyridines.Base on the structural characteristics of the products and the stereoselectivity of the reaction,the asymmetric reaction conditions were optimized.First,the photochemical conditions of asymmetric synthesis of 2,3-dihydropyrrole with 1,4-dihydropyridines were discussed in the relationships of the factors of photoreaction?wavelength,solvent,reaction temperature and oxygen?and the structures of products.The structural characteristics and stereoselectivity of the products were analyzed by the NMR spectroscopy and X-ray diffraction.Second,the asymmetric photochemical reaction of 1,4-dihydropyridines with a chiral auxiliary was discussed in the results of the chiral auxiliary on the stereoselectivities of 2,3-dihydropyrroles.Finally,the mechanism of asymmetric photochemical synthesis of 2,3-dihydropyrroles with1,4-dihydropyridines were speculated as a photooxidation rearrangement.The1,4-dihydropyridines were photooxidated to 2,3-dihydropyrroles by the singlet oxygen diastereoselectively.The introduction of chiral auxiliaries can induce the diastereoselectivity of asymmetric synthesis of 1,4-dihydropyridine.The chiral effect of chiral auxiliaries can maintained in the final products.The roles of chiral auxiliaries were to make 1,4-dihydropyridines with diastereoselectivities.The absolute configuration of the induced chiral center could induce the configurations of the new chiral centers in the process,so as to achieve the asymmetric synthesis of the photochemical reaction.Through the study on the asymmetric photochemical synthesis of2,3-dihydropyrroles,fifteen 1,4-dihydropyridines and two 1,4-dihydropyridines with optical purity,thirteen 2,3-dihydropyrroles and one?2R,3R?-3-aryl-1-acetyl-2-hydroxyl-5-methyl-2,3-dihydropyrrole-2,4-dicarboxylic ester were obtained and confirmed by¹HNMR,¹³CNMR,HRMS and X-ray Diffraction.