Stereoselective Synthesis of 2,4,5-Trisubstituted Piperidines via Radical Cyclization
作者:Maria-Eleni Ragoussi、Stephen M. Walker、Andrea Piccanello、Benson M. Kariuki、Peter N. Horton、Neil Spencer、John S. Snaith
DOI:10.1021/jo101631y
日期:2010.11.5
A novel approach to 2,4,5-trisubstituted piperidines is reported, involving the 6-exo cyclization of stabilized radicals onto alpha,beta-unsaturated esters. Only two of the four possible diastereoisomers are observed, with diastereomeric ratios ranging from 3:2 to 40:1 when the radical stabilizing group is vinyl or phenyl. Cyclization of a (triethylsilyl)vinyl-stabilized radical gives the corresponding piperidine radical as a single diastereoisomer that may either be trapped by tributyltin hydride to afford the 2,4,5-trisubstituted piperidine or undergo a second 5-endo cyclization onto the (triethylsilyl)vinyl substituent to produce the 3,5,7-trisubstituted octahydro[2]pyrindene as a single diastereoisomer.