Stereocontrolled synthesis of (+)-α-skytanthine by means of an intramolecular Pauson–Khand reaction

Diastereoselective synthesis of (+)-α-skytanthine was established by means of an intramolecular Pauson–Khand reaction of N-but-2-yn-1-yl-N-[(2R)-2-methylbut-3-en-1-yl]-1-(2-nitrobenzene)sulfonamide, in which the newly generated stereogenic center was stereoselectively constructed to be R by reflection of the stereochemistry of the methyl group in the starting material.