[4+2] Cycloaddition of 2-Substituted 1,2-Dihydropyridines with Nitrosobenzene:Asymmetric Synthesis of trans-2-Substituted 3-Amino-l,2,3,6-tetrahydropyridines

摘要

A new methodology for the stereoselective synthesis of trans-2-substituted 3-amino-l,2,3,6-tetrahydropyridines is reported.The preparation of these 3-aminopiperidines is achieved by cycloaddition of nitrosobenzene with 2-substi-tuted 1,2-dihydropyridines followed by chemoselective reduction of the cycloadducts.Enantioenriched 1,2-dihydro-pyridine derivatives are easily prepared from pyridine and a chiral amide following a previous report from our laboratories.Moreover,the in situ hydrogenation of these cycloadducts over palladium in a solution of hydrogen chloride in methanol led to tetrahydropyrroloimidazoles.