Study On The Paternò-büchi Reaction Of Isocoumarins And Quinones Driven By Visible Light And The Rearrangement Of Oxetanes

Photochemical reaction is a kind of mild and environmentally friendly reaction.Specifically,photochemical reaction driven by visible light makes an outstanding contribution to "green chemistry".Among these phototransformations,the Paternò-Büchi reaction between the excited carbonyl compound and alkene is the classical method to afford oxetane,which is a scaffold for molecules with excellent biological activities.In this thesis,the PB reaction of isocoumarins with quinolones or naphquinones was mediated using blue LED light as the light source and organic dye as the photocatalyst.A series of oxetane compounds were synthesized with high chemo-selectivity,regio-selectivity and diastereo-selectivity.This method overcomes the decomposition of the oxetanes caused by UV-induced disscociation and reduces the dimerization of starting materials,which greatly improves the yields.Additionally,the rearrangement of oxetanes to access spiroisocoumarins was achieved.The research of this thesis mainly includes the following aspects:1.We were using the eight isocoumarin derivatives and,one benzofurans with seven quinolinones and two naphthoquinones for visible light medaited PB reactions.After the reaction conditions are optimized,totally 32 reactions,39 oxetanes or 4 cyclobutanes were obtained.The absolute configurations of several representative compounds were determined by X-ray diffraction analysis.And the mechanism is roughly proposed.The high chemo-selectivity and regio-selectivity of oxetane can be favored by the presence of halogens or alkoxy groups on the 3-position substituents of isocoumarin.Meanwhile,the electron-withdrawing substituents on the quinolinone can enhance the regio-selectivity of the PB reaction.2.We found that the oxetanes obtained above can undergo intramolecular isomerization under appropriate Lewis acid catalysis to afford spirals.We optimized the reaction conditions and synthesized 33 spirals by one-pot reaction under the radiation of visible light.The configuration of typical compounds was determined by X-ray diffraction analysis.We made a simple proposal for the reaction mechanism.The substituents on the 3-postion of isocoumarins are the transportable halogens and alkoxy groups enable the rearrangment,in contrast,the unsubstituted isocoumarin and 4-bromoisocoumarin cannot afford the expected products.The N atom on quinolones leads to higher regio-selectivity than naphthoquinones in this transformation,which can be attributed to its electronic property and potential coordination effect.3.An efficient,rapid and clean synthetic method for the synthesis of3-phenylbenzofurans was approached by Eaton’s reagent using α-phenoxyketone as starting materials.We investigated the effect of reaction temperature on the reaction and synthesized 30 3-phenylbenzofurans compounds with good to excellent yields of 50-98 %.Two benzocoumarins,benzothiophene and benzopyran can also be synthesized by this method.