Study On Cyclization Of Oxiranes Via Lewis Acid Catalyzed C-C Bond Cleavage As Well As Transition-Metal-Free B-B Bond Activation

Construction of complicated structure or activation of inert bonds with less expensive or even without transition-metal salts has received a lot of attentions during the past decades along with the rapid development of organic synthesis oriented organometallic chemistry. The following work was carried out based on this concept.There are two corresponding parts included in this thesis.Part I:Cyclization of Oxiranes via Lewis Acid Catalyzed C-C Bond CleavageFused indolines are frequently found in a large number of biologically active alkaloids, research on new methods to build these skeletons is of great importance and interests. Here we prepared a series of substituted aryl dicarboxyl oxiranes which can be converted into the active intermediate species, carbonyl ylide, via Ni(ClO4)2·6H2O catalyzed C-C bond cleavage of the oxirane. Indoles were introduced to trap these intermediate species to form the1H-furo[3,4-b]indole products with a high diastereoselectivity. A demethoxycatboxylated product with four contiguous stereocenters could also be easily and selectively obtained. In addition, the preliminary results showed enantioselectivity can be achieved in this Lewis acid catalyzed [3+2] cycloaddtion.Part II:Transition-Metal-Free B-B Bond ActivationAryl boronic esters have been considered as essential synthetic blocks to easily form carbon-carbon or carbon-heteroatom bond over the past decades. We successfully demonstrated the borylation of aryl iodides without additional transition metal salts. This reaction can tolerate a series of functional groups under this CsCO3/MeOH system. The preliminary mechanism study indicated this process is neither copper-catalyzed nor radical mediated. These results would be helpful to enrich our understanding of this type of reaction.