An efficient diastereo- and enantioselective synthesis of syn-2,3-disubstituted 1,4-diketones 4 is described. Key step of the procedure is the oxidative coupling of the metalated SAMP/RAMP-hydrazones 2 with iodine, followed by oxidative cleavage of the dimerized bishydrazones 3 with ozone and subsequent separation of the minor meso-isomer by chromatography. The d,l-isomers of the title 1,4-diketones 4 are obtained in good overall yields (20-64%) and high diastereo- and enantiomeric excesses (de ≥ 98%, ee = 80- ≥ 95%).
本文描述了syn-2,3-二取代-1,4-二酮4的高效对映选择性和非对映选择性合成方法。该过程的关键步骤是
金属化的
SAMP/
RAMP脒2与
碘的氧化耦合反应,随后用
臭氧氧化断开二聚的双脒3,并通过色谱法分离出次要的内消旋异构体。标题1,4-二酮4的d,l异构体以良好的总收率(20-64%)和高度的非对映选择性及对映体过量(de ≥ 98%,ee = 80- ≥ 95%)获得。