Stereoselective construction of cis-2,6-disubstituted tetrahydropyrans via the reductive etherification of δ-trialkylsilyloxy substituted ketones:: Total synthesis of (-)-centrolobine

[GRAPHICS] The stereoselective intramolecular reductive etherification of delta-trialkylsilyloxy substituted ketones with catalytic bismuth tribromide and triethylsilane provides a convenient method for the construction of cis-2,6-disubstituted tetrahydropyrans. This method was highlighted in the key step of an expeditious total synthesis of the antibiotic, (-)-centrolobine.