Dual Catalysis in Enantioselective Oxidopyrylium-Based [5 + 2] Cycloadditions
datasetposted on 21.09.2011, 00:00 by Noah Z. Burns, Michael R. Witten, Eric N. Jacobsen
A new method for effecting catalytic enantioselective intramolecular [5 + 2] cycloadditions based on oxidopyrylium intermediates is reported. The dual catalyst system consists of a chiral primary aminothiourea and a second achiral thiourea. Experimental evidence points to a new type of cooperative catalysis with each species being necessary to generate a reactive pyrylium ion pair that undergoes subsequent cycloaddition with high enantioselectivity.