Abstract
A highly enantioselective catalytic Diels- Alder (DA) cycloaddition of 2H-pyran-2,5-diones (synthon of 5-hydroxy-2-pyrones) has been devel- oped with a Cinchona-derived thiourea as the cata- lyst. The conditions were optimized by using 0.2 equiv. of the catalyst and 0.1 equiv. of formic acid in 2-propanol at room temperature, which afforded the DA products in yields of up to 90% (exo/endo = 5.5:1, 98% ee) with trans-b-nitrostyrene derivatives as the dienophiles. The structure/activity relation- ships of the bifunctional catalyst and the effects of the steric, electronic and hydrogen-bonding proper- ties of the dienophiles have been studied.
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