A new pathway to chiral tetracyclic indolidines via Pauson–Khand reaction

Reaction of enynes 1 and 3 with Co2(CO)8 in the presence of DMSO, NMO or TMANO as promoters produced tricyclic indolidine derivatives 5 and 7 stereoselectively in moderate to excellent yield. The stereochemistry at the C-7 position of the indolidines 5 and 7 was confirmed by their conversion into the bridged azacycles 10 and 13.