A Convenient General Access to Methyl 2-Chloro-2-cyclopropylidenacetates, Reactive Michael Acceptors and Cycloaddends

The reaction of 1-chloro-1-(trichlorovinyl)cyclopropanes 1 with potassium hydroxide/methanol or sodium methoxide/methanol yields trimethyl 2-chloro-2-cyclopropylidenorthoacetates 7, which can be quantitatively converted to the corresponding esters 8 by acid treatment. The methyl 2-chloro-2-cyclopropylidenacetates 8 are highly reactive Michael acceptors, which readily undergo 1,4-addition with soft nucleophiles such as thiophenolate, secondary amines, azide, cyanide, and lithium dimethylcuprate. The reactivity, however, is influenced by substituents on the cyclopropane ring, the unsubstituted compound 8j reacting 86 times faster with thiophenolate than the tetramethyl derivative 8a, which in turn is 2.5 times as reactive as methyl 3,3-dimethylacrylate 16. Compound 8j is a reasonably reactive cycloaddend in both [2+2]- and [2+4]-cycloadditions.