作者:Jan Bräckow、Klaus T. Wanner
DOI:10.1016/j.tet.2005.11.069
日期:2006.3
based on the trapping reaction of 4-substitued N-silylpyridinium ions. When performed with dialkylmagnesium reagents, such as iPr2Mg, silyl protected 4,4-disubstituted 1,4-dihydropyridines were obtained in up to quantitative yields. High 1,4-selectivity was found for sterically demanding nucleophiles, whereas small nucleophiles (Me2Mg) tend to yield 1,2-addition-products. Grignard, dialkylzinc and organocopper
提出了制备4,4-二取代的1,4-二氢吡啶的空前的方法。它基于4-取代的N-甲硅烷基吡啶鎓离子的捕集反应。当与二烷基镁试剂,如执行我镨2的Mg,甲硅烷基保护4,4-二取代的高达定量的产率得到1,4-二氢吡啶。发现对空间要求高的亲核试剂具有较高的1,4-选择性,而小的亲核试剂(Me 2 Mg)倾向于产生1,2-加成产物。发现格氏试剂,二烷基锌和有机铜试剂没有产生加成产物或产生较差的结果。在HCl存在下,用NaCNBH 3还原获得的1,4-二氢吡啶,然后用二碳酸叔丁酯以高收率提供了相应的N- Boc保护的哌啶。