Synthesis 2006(13): 2139-2142  
DOI: 10.1055/s-2006-942420
PAPER
© Georg Thieme Verlag Stuttgart · New York

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

Elizabeth A. Uhricha, William A. Batsona, Marcus A. Tius*a,b
a 2545 The Mall, University of Hawaii, Honolulu, HI 96822, USA
b The Cancer Research Center of Hawaii, 1236 Lauhala Street, Honolulu, HI 96813, USA
Fax: +1(808)9565908; e-Mail: tius@gold.chem.hawaii.edu;
Further Information

Publication History

Received 29 April 2006
Publication Date:
12 June 2006 (online)

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.

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.