Diastereoselective cobalt-assisted Ferrier-type rearrangement to construct chiral alkynyl cyclohexanones

Functionalized 1-C-alkynyl sugars are prepared from 2-acetoxy-glucal triacetate. Dicobalt complexes of these sugar acetylenes can stabilize the anomeric carbenium cations, which promote the Ferrier-type rearrangement through the 5,6-dehydro precursors to afford alkynyl cyclohexanones after decomplexation. High stereoselectivity resulted from suitable steric interaction between the C-2 O-protecting group and the alkynyl substituents. Molecular mechanism is discussed.

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