Studies On The Total Synthesis Of Laevinoids A And B And The Enantioselective Bromocyclization

This thesis was concerned with the studies on the total syntheses of natural products Laevinoids A and B, and the enantioselevtive bromocyclization, accordingly, the main content of this thesis can be divided into the following two parts:Part one:Studies on the Total Synthesis of Laevinoids A and BLaevinoids A and B were first isoliated by Yue group from Croton laevigatus Vahl. They introduced the structure characteristics of Laevinoids A and B. Based on the structure analysis of Laevinoids A and B, we designed two different strategies to syntheses these two natural products.In the first synthetic route, we planed to construction the main skeleton of Laevinoids A and B using several classical reactions, including Wittig reaction, ester exchange reaction and carbene insertion cycloaddition reaction. However, when we put this route into practice, the Wittig reaction turned to be our biggest problem. We tried many reaction conditions, no desired product was observed. So we reconsider the synthetic route, and modified our original design.In the second route, we planed to use carbene insertion cycloaddition reaction as key reaction as well. We designed two segments as key intermediates (compound 1 and 2), then combine 1 and 2 by ester exchange reaction. The following reactions include DA reaction, carbene insertion cycloaddition reaction. By far, we already synthesized key intermediate 1, key compounds 1-28, 1-30. Further work is currently in progress.Part two:Studies on the Enantioselective Bromocyclization.Significant progress has been recorded in the past three years in the development of catalytic, enantioselective versions of alkene halofunctionalizations with the four common halogens. However, by any yardstick, the field has only just started to take shape. A number of factors conspire to stimulate continued interest:the importance of stereodefined, halogenated compounds in natural and unnatural products, the bounty of well-established reactivity of the carbon-halogen bonds, and the opportunities to discover new mechanisms of catalysis and stereoinduction. On the basis of previous research, we designed a series of enantioselevtive bromocyclization reactions, meanwhile, we also designed and synthesized several chiral catalysts, and applied them to these reactions. By far, we have accomplished the syntheses of catalysts 1a, 1b,2a,2b,2c,3a,3b, and the syntheses of compounds 2-1,2-2,2-3 (substrates of the designed enantioselevtive bromocyclization reactions). We tried a series of reaction conditions (bromine sources, temperature), but still failed in the obtainment of the desired cyclization products. Further work is currently still in progress.