versatile chiral building block. The strategy is based on three key transformations: enantioselective hetero-Diels−Alder (HDA) reaction of aldehyde with Danishefsky’s diene, selective reduction of carbonyl function, and Claisen or related rearrangement. The synthetic utility of the methodology is illustrated by totalsynthesis of antibiotic (−)-centolobine.
Enantioselective Synthesis of 2,6-<i>cis</i>-Disubstituted Tetrahydropyrans via a Tandem Catalytic Asymmetric Hydrogenation/Oxa-Michael Cyclization: An Efficient Approach to (−)-Centrolobine
A highly efficient one-pot process via a tandemreaction of catalytic asymmetric hydrogenation and oxa-Michael cyclization for the synthesis of 2,6-cis-disubstituted tetrahydropyrans has been developed (ee up to 99.9%, cis/trans-selectivity up to 99:1). This method provides a concise route to (−)-centrolobine (68.8% yield, three steps).