Asymmetric synthesis of highly functionalized tetrahydropyrans via a one-pot organocatalytic
Robert Hahn1, Gerhard Raabe, Dieter Enders
1Institute of Organic Chemistry, RWTH Aachen University , Landoltweg 1, 52074 Aachen, Germany.
Abstract:
A diastereo- and enantioselective Michael/Henry/ketalization sequence to functionalized tetrahydropyrans is described. The multicomponent cascade reaction uses acetylacetone or β-keto esters, β-nitrostyrenes, and alkynyl aldehydes as substrates affording tetrahydropyrans with five contiguous stereocenters. Employing a bifunctional quinine-based squaramide organocatalyst, the title compounds are obtained in moderate to good yields (27-80%), excellent enantiomeric excesses (93-99% ee), and high diastereomeric ratios (dr > 20:1) after one crystallization.
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