Synthesis of 3,5-dichlorocyclopentane-1,2,4-trione

Abstract

In continuation of our studies on the synthesis and properties of chlorinated cyclopentenones derived from hexachlorocyclopentadiene [1, 2], in the present communication we describe the synthesis of 3,5-dichlorocyclopentane-1,2,4-trione (Ia) as a new derivative of cyclopentane-1,2,4-trione (IIa). Although parent completely enolized trione IIa has long been known [3–5], published data on its reactions are relatively poor. Known examples include only some simplest transformations of trione IIa, such as reactions with amines, diazomethane, methanol under acidic conditions, and dimethyl sulfoxide [6], as well as prostaglandin syntheses starting from substituted cyclopentanetriones [7, 8]. According to [4, 5], cyclopentanetrione IIa can exist as enol tautomers IIb and IIc (Scheme 1). taking into account additional activation of the CH protons by chlorine atoms; furthermore, compound Ib should be more acidic than IIb (pKa 3.0) [5]. The spectral parameters of compound Ia suggest that it exists as only one of the two possible enol tautomers, namely enol Ib (Scheme 2). Therefore, trione IIa was also assumed to have enol structure IIb, and this structure was confirmed by comparison of the spectral data for its methylation product, 2,4-dichloro-5-methoxycyclopent-4-ene-1,3-dione (V) with those for structurally related compounds [1]. ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 12, pp. 1885–1887. © Pleiades Publishing, Ltd., 2010. Original Russian Text © N.A. Ivanova, K.S. Kislitsina, M.S. Miftakhov, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46, No. 12, pp. 1870–1872.