Synthesis of 3,4-Disubstituted Piperidines by Carbonyl Ene and Prins Cyclizations: A Switch in Diastereoselectivity between Lewis and Brønsted Acid Catalysts
作者:Jodi T. Williams、Perdip Singh Bahia、John S. Snaith
DOI:10.1021/ol0266929
日期:2002.10.1
[GRAPHIC]A novel diastereoselective approach to cis and trans 3,4-disubstituted piperidines is described. Carbonyl ene cyclization of aldehydes 6a-e catalyzed by the Lewis acid methyl aluminum dichloride in refluxing chloroform affords trans piperidines 8a-e with diastereomeric ratios of up to 93:7. By contrast, Prins cyclization of 6a-e catalyzed by hydrochloric acid at low temperatures affords cis products 7a-e with diastereomeric ratios of up to 98:2.
Synthesis of 3-Substituted 4-Piperidinones via a One-Pot Tandem Oxidation−Cyclization−Oxidation Process: Stereodivergent Reduction to 3,4-Disubstituted Piperidines
作者:Perdip S. Bahia、John S. Snaith
DOI:10.1021/jo0357418
日期:2004.4.1
A novel approach to 3-substituted 4-piperidinones is described. The one-pot tandem oxidation - cyclization - oxidation of unsaturated alcohols 1a-e by PCC or PCC and trifluoromethanesulfonic acid affords piperidinones 2a-e in good yield. Reduction of 2a-e by L-Selectride gives the corresponding cis 3,4-disubstituted piperidines with diastereomeric ratios of >99:1. By contrast, reduction of 2a-e by Al-isopropoxydiisobutylalane gives the trans products with diastereomeric ratios of up to 99:1.
Synthesis of 3,4-Disubstituted Piperidines by Carbonyl Ene and Prins Cyclizations: Switching between Kinetic and Thermodynamic Control with Brønsted and Lewis Acid Catalysts
作者:Jodi T. Williams、Perdip S. Bahia、Benson M. Kariuki、Neil Spencer、Douglas Philp、John S. Snaith
DOI:10.1021/jo052532+
日期:2006.3.1
to cis and trans 3,4-disubstituted piperidines is described. Carbonyl ene cyclization of aldehydes 4a−e catalyzed by MeAlCl2 in refluxing chloroform afforded the trans piperidines 7a−e with diastereomeric ratios of up to 93:7, while aldehyde 4f afforded solely the cis product 6f, which was resistant to isomerization to the trans isomer. It was demonstrated for 4a that the cyclization catalyzed by a