Stereoselective synthesis of 2,4,5-trisubstituted piperidines via radical cyclization |
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Authors: | Ragoussi Maria-Eleni Walker Stephen M Piccanello Andrea Kariuki Benson M Horton Peter N Spencer Neil Snaith John S |
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Institution: | School of Chemistry, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. |
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Abstract: | A novel approach to 2,4,5-trisubstituted piperidines is reported, involving the 6-exo cyclization of stabilized radicals onto α,β-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 octahydro2]pyrindene as a single diastereoisomer. |
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