Study On The Intramolecular Cyclization Reactions Of Oxiranes And Aziridine

Six membered N/O containing heterocycles are present in many natural products and medicinal molecules with biological activity, and have been widely used as building blocks in synthesis of complex natural pruducts and drug molecules. Therefore, it is very important to develop some novel and efficient reactions for synthesis of these heterocycles. On the other hand, as important building blocks for organic synthesis and subunites, oxiranes and aziridines have high reactivity due to their highly strained three-membered ring and have been applied to synthesis of heterocycles. In general, the dominant chemistry of oxiranes and aziridines is ring opening via C-O bond cleavage and C-N bond cleavage, reapectively, while C-C bond cleavage of oxiranes and aziridines are notable exceptions due to the relatively lower energy barrier of C-hetero atom compared to the C-C bond. In general, the C-C bond cleavage takes place under thermo or photochemistry leading to low selectivity. Therefore, it’s of great importance to achieve selective C-C bond cleavage under mild conditions. Based on the recent progress in oxirane and aziridine chemistry in other group, we did the following work:1) synthesis of isochromanones and isoquinolines via tandem oxirane/aziridine ring opening/Friedel-Crafts cyclization,2) synthesis of oxazino [4,3-a] indoles and oxazino [4,3-a] pyrroles via tandem oxirane ring opening/Friedel-Crafts cyclization.In the chapter Ⅱ, we synthesized oxiranes and aziridines bearing electron-rich aromatic rings or olefins, which proceeded selective C-C bond heterolysis via Yb(OTf)3-catalyzed ring opening to afford the resulted ylides, which underwent further Friedel-Crafts cyclization to abtain isochromanones and isoquinolines with high chemoselectivity and moderate diastereselectivity, respectively. Additionally, alkylation, triflation of isochromanones and elimination of isoquinolines can be easily operated in one-pot synthesis, which have potential utilities in organic synthesis. In the chapter III, we synthesized oxiranes bearing indole and pyrroles, which proceeded selective C-C bond heterolysis via Sc(OTf)3-catalyzed ring opening and Friedel-Crafts cyclization to afford oxazino [4,3-a] indoles and oxazino [4,3-a] pyrroles with high chemoselectivity and moderate diastereselectivity. Additionally, further alkylation and decarbonation can proceed smoothly.