Robinson Annulation

The Robinson Annulation is a useful reaction for the formation of six-membered rings in polycyclic compounds, such as steroids. It combines two reactions: the Michael Addition and the Aldol Condensation

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Mechanism of the Robinson Annulation

The first step in the process is the Michael Addition to an α,β-unsaturated ketone, such as methyl vinyl ketone (ethyl vinyl ketone is shown above):

The newly formed enolate intermediate must first tautomerize for the conversion to continue:

The subsequent cyclization via Aldol Addition is followed by a condensation to form a six-membered ring enone:

Robinson Annulation can also proceed under acidic catalysis, with the entire process occurring in one pot, as shown below. The use of a precursor of the α,β-unsaturated ketone, such as a β-chloroketone, can reduce the steady-state concentration of enone and decrease the side reaction of polymerization.

a) C. H. Heathcock, J. E. Ellis, J. E. McMurry, A. Coppolino, Tetrahedron Lett., 1971, 12, 4995. DOI
b) C. H. Heathcock, C. Mahaim, M. F. Schlecht, T. Utawanit, J. Org. Chem., 1984, 49, 3264.

Recent Literature

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