Reactions of ketenes with ethoxyalkynes: Synthesis of 2,2,4-trialkylcyclobutane-1,3-diones

Treatment of dimethyl ketene with ethoxyacetylene 1a, 1-ethoxyoct-1-yne 1b, and 1-ethoxytetrade-1-yne 1c afforded the 3-ethoxycyclobutenones 2a–c. Hydrolysis of 2a–c with dilute hydrochloric acid gave the cyclobutane-1,3-diones 3a–c. The ¹H NMR spectra of these compounds indicate that in CDCl₃ solution 2,2-dimethylcyclobutane-1,3-dione 3a exists as the diketone, whereas the 2,2,4-trialkylcyclobutane-1,3-diones 3b and 3c exist as the monoenols.