The hexacarbonyl dicobalt complex of the acetylene thioether derived from (2R)exo-10-(methylthio)-2-bornanethiol has been prepared in good yield. This compound affords a stable internally chelated pentacarbonyl complex either by thermal or oxidative decarbonylation. Optimal conditions for the highly diastereoselective reaction of the chelated species have been developed. (C) 1997 Elsevier Science Ltd. All rights reserved.