【摘要】 首次研究了Cu(CH3CN)4BF4/DTBM-BIPHEP催化的亚甲胺叶立德与环丙基亚甲基乙酸乙酯参与的不对称1,3-偶极环加成反应,获得了优异的exo-选择性,研究结果证实大空间位阻的手性双膦配体对反应的非对映选择性控制起到至关重要的影响;同时一步高效构建三个叔碳手性中心和一个螺环季碳中心.该不对称1,3-偶极环加成反应收率良好,得到优秀的非对映(>98∶2,dr)与对映选择性(ee值高达99%).该催化体系为合成exo构型的5-氮杂-螺[2,4]庚烷衍生物提供了一种简洁高效的方法,具有原子经济性好、反应条件温和、底物适用范围广等优点.更多还原

【Abstract】 A direct and facile access to highly functionalized 5-aza-spiro[2,4]heptane derivatives is developed via Cu(CH3CN)4BF4/DTBM-BIPHEP-catalyzed asymmetric exo-selective 1,3-dipolar cycloaddition of azomethine ylides with ethyl cyclopropylidene acetate for the first time. The Cu(CH3CN)4BF4/DTBM-BIPHEP complex was identified as the optimal catalyst for the exo-selectivity. The reaction was carried out smoothly with wide substrate scope, and electron-deficient, electron-neutral and electron-rich aryl substituted imino esters were all compatible with the reaction, affording the 5-aza-spiro[2,4]heptane adducts containing three tertiary stereogenic centers and one spiro quaternary center in moderate to good yield(53%~83%) with excellent diastereoselectivity(>98∶2, dr) and high enantioselectivity(up to 99% ee). The less reactive alkyl substituted imino ester derived from butyraldehyde was also tolerated in this annulation. The absolute configuration of the cycloadduct was unequivocally determined to be(4R,6S,7S) by X-ray analysis of N-tosylated derivative of exo-3a. Based on the relative and absolute configuration of the exo-cycloadducts, we proposed that an exo approach of ethyl 2-cyclopropylidene acetate to the copper(I) complex occurred predominantly because of the disfavored steric repulsion generated in the endo approach between the substituents of ethyl 2-cyclopropylidene acetate and the large bulky aryl group on the phosphorus atom of the chiral ligand. The produced 5-aza-spiro[2,4]heptanes fragment is widely present in many bioactive carbapenems derivatives, HSR-903 and substituted oxazolidinones. The optically active compounds with different stereoselectivities show different biological activities, therefore, it is important to develop the atom economical method for the asymmetric synthesis of biologically active exo-selective 5-aza-spiro[2,4]heptane derivatives.更多还原