Reactivity enhancement through strain and electronic effects: α-heterocyclopropylidenacetates as powerful Michael acceptors

The new α-thiosubstituted cyclopropylidenacetates 2c, d have been synthesized from 2a. The relative reactivities of 2a, b, c, d, their substituted analogues 4a and 3,3-dimethylacrylate (7) towards thiophenolate were determined by competition experiments. Both ring strain and α-heterosubstituents drastically enhance the reactivity. 2c readily undergoes cycloaddition to cyclopentadiene and addition of carbon nucleophiles at room temperature.