Facile Access to cis-2,6-Disubstituted Tetrahydropyrans by Palladium-Catalyzed Decarboxylative Allylation: Total Syntheses of (±)-Centrolobine and (+)-Decytospolides A and B

cis-2,6-Tetrahydropyran is an important structural skeleton of bioactive natural products. A facile synthesis of cis-2,6-disubstituted-3,6-dihydropyrans as cis-2,6-tetrahydropyran precursors has been achieved in high regioand stereoselectivity with high yields. This reaction involves a palladium-catalyzed decarboxylative allylation of various 3,4-dihydro-2H-pyran substrates. Extending this reaction to 1,2-unsaturated carbohydrates allowed the achievement of challenging b-C-glycosylation. Based on this methodology, the total syntheses of (+/-)-centrolobine and (+)-decytospolides A and B were achieved in concise steps and overall high yields.