Cyclizations of α-Diketones to α-Hydroxycyclopentenones on Silica Gel in the Absence of Solvent

Abstract

Stirring α,β-unsaturated α-diketones in the presence of activated silica gel results in cyclization to α-hydroxycyclopentenones in good yield. The reaction is sensitive to the mode of stirring and proceeds more rapidly in the presence of triethylamine. This is consistent with a Nazarov reaction proceeding through the enol tautomer of the α-diketone.

Key words

diketones - cyclizations - Nazarov reactions - silica gel - rearrangements

References

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7

Professor Marvin J. Miller (Notre Dame) had suggested that a trace metal oxide present as a contaminant in silica gel, possibly iron, was responsible for catalyzing the cyclization reaction. The silica gel manufacturer’s (Natland International Corporation) certificate of analysis indicated ‘less than 0.02% iron’ (<200 ppm) and our independent determination (Desert Analytics) indicated 0.03% (300 ppm) iron. Iron is certainly present, probably as Fe(III) oxide; therefore we cannot exclude this possibility.