An active methyne compound is a compound that has the following general structural formula.
E1, E2 = a functional group that withdraws electrons by resonance
R= alkyl, aryl
The conjugate base of an active methyne compound is highly resonance stabilized.
Consequently, active methyne compounds, like active methylene compounds, are highly acidic and can be deprotonated, for all practical purposes, irreversibly, using common strong bases, such as the hydroxide ion or alkoxide ions.