Reaction of Organic Halides with Chlorotris-(triphenylphosphine) cobalt (I)

Abstract

Reaction of various types of organic halides with a monovalent cobalt complex, chlorotris (triphenylphosphine) cobalt (I) is described. Reaction of benzylic monohalides, dihalides and trihalides with CoCl (Ph₃P)₃ gave a coupling product with formation of a carbon-carbon single bond, double bond and triple bond, respectively, under mild and non-basic conditions. Dehalogenation of non-benzylic vicinal dihalides with the reagent took place cleanly to give an olefin in high yield. Reductive coupling of allylic halides using the reagent afforded regioselectively a 1, 5-diene with retention of the stereochemistry of the carbon-carbon double bond of the allylic halides used. By using this reaction, (E, E, E, E)-squalene was stereospecifically synthesized from (E, E)-farnesyl bromide. Reaction of halohydrins with CoCl (Ph₃P)₃ gave exclusively a ketone in the presence of an amine or olefin through an alkylcobalt intermediate. A 1, 2-hydrogen shift is involved in this reaction.