A diastereoselective synthesis of trans-2-alkyl-6-aryl-3,6-dihydro-2H-pyrans has been described. Dehydrogenative cycloetherification of (E)-(±)-1-aryl-5-hydroxy-1-alkenes promoted by DDQ proceeded cleanly via 6-endo cyclization to afford trans-2-alkyl-6-aryl-3,6-dihydro-2H-pyrans (32 examples) in good yield (up to 89%) and with moderate to excellent diastereoselectivity (up to 99:1). The synthetic utility of the method was illustrated by the second total synthesis of (±)-(2R,6S)-3,4-dehydro-1,7-bis(4-hydroxy phenyl)-4′de-O-methyl centrolobine and a total synthesis of (±)-centrolobine.
We gratefully acknowledge financial support of this work by the Basic Science Research Program through the National Research Fund of Korea (NRF) funded by the Ministry of Education (NRF-2018R1D1A1A02086359). We also thank Ms. Jina Gim (College of Pharmacy, Ajou University) for preparing some starting materials.
