The dicobalt hexacarbonyl(alkyne) moiety as a stereocontrol element in intramolecular Friedel–Crafts alkylations1

Abstract
A dicobalt hexacarbonyl(alkyne) moiety is used as a stereocontrol element in Friedel–Crafts cycloalkylation reactions that deliver cis-4a-ethynyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrenes exclusively.