[4 + 2] Cyclocondensation Reactions of Tungsten–Dihydropyridine Complexes and the Generation of Tri- and Tetrasubstituted Piperidines

A new method for the preparation of functionalized piperidines is described in which various dihydropyridine (DHP) complexes of {TpW(NO)(PMe3)} that are derived from pyridine–borane undergo [4 + 2] cyclocondensation with enones, enals, nitrosobenzene, and several isocyanates to form [2.2.2] bicyclic species. In several cases the diazabicyclooctene products derived from DHP complexes and isocyanates can be further elaborated into novel syn-2,5-disubstituted and 2,3,6-trisubstituted piperidinamides.

本研究报道了一种制备官能化哌啶的新方法。该方法中，由吡啶-硼烷衍生得到的{TpW(NO)(PMe3)}的各类二氢吡啶（DHP）配合物，可与烯酮、烯醛、亚硝基苯以及多种异氰酸酯发生[4+2]环缩合反应，生成[2.2.2]双环物种。在部分案例中，由DHP配合物与异氰酸酯反应得到的二氮杂双环辛烯产物，可进一步衍生为新型顺式-2,5-二取代及2,3,6-三取代哌啶酰胺。