Cyclisation of esters of monoalkylacetonedicarboxylic acids. Isolation of a 4-oxo-4H-pyran-3-sulphonic acid

Abstract

Treatment of diethyl 2-methyl-3-oxopentanedioate or its 2-ethyl analogue with fuming sulphuric acid affords a 4-oxo-4H-pyran-3-sulphonic acid. Spectroscopic evidence suggests that these products may be better represented as pyrylium-3-sulphonates or as mixtures of uncharged and dipolar tautomers. The 3-sulphonic acid of 2,6-dimethyl-4H-pyran-4-one has also been prepared, but attempts to prepare the 3-sulphonic acid of 2-methoxy-6-methyl-4H-pyran-4-one have been unsuccessful.