P-36 隣接位に酸素官能基を有するビシナルジブロミドの脱離反応を利用した生理活性天然物の全合成研究(ポスター発表の部)

抄録

2-Bromo-1-alkenes have been recognized as one of useful functional groups for preparation of vinyl lithiums and vinyl Grignard reagents, for coupling partners in a wide range of transition metal-mediated coupling reactions, substrates of radical reaction, and precursors of α-haloketones. Selective elimination reaction of 1,2-dibromides possessing O-aryl or O-acyl groups at the C3 position into 2-bromo-1-alkenes under mild basic conditions was developed. It can be explained that this regioselective elimination proceeds by inducing the acidity of hydrogen atom at the C2 position by the electron-withdrawing effect of the oxygen functional group at the adjacent position. Even in the case of vicinal dibromoalkane units at internal positions in carbon chain, a similar regioselective trans-elimination reaction took place, despite the syn- or anti-orientation of vicinal dibromides. As application of this regioselective elimination reaction, total synthesis of biologically active natural products, such as 12-oxygenated-tremetones, tuliparin B, and tanikolide, were accomplished. In addition, a synthetic study on seco-germacrane lactone by using the regioselective HBr elimination reaction and Pd-mediated coupling reaction as key steps was carried out. Alkynes are also one of the important functional groups as precursors of cis- and trans-1-iodo-1-alkenes, 2-iodo-1-alkenes, metalated alkenes and alkynes, and for substrates of organometal-conducted coupling reactions. HBr elimination reactions of 1,2-dibromides using LiHMDS, NaNH_2, etc., have been reported as synthetic methodologies of terminal alkynes. However, carbonyl functions such as lactones and ketones would react under the conventional methods. During our extensive investigation, the acidity enhancement of hydrogen at the C1 position by O-functional groups at the C3 position was also observed. This observation indicated a new prospective synthesis of alkynes from 1,2-dibromides under the DBU conditions. As demonstration of the versatile availability of the alkyne-syntheses condition, total syntheses of biological active lactone natural products muricatacin and (R,R)-sapinofuranone B were successfully achieved.