Tetracyanoethylene dicyanoketene acetal

Next to iodine there is also another class of neutral Lewis acids known. Tetracyanoethylene, dicyanoketene acetals and derivatives can catalyse reaction due to their tt-Lewis acid properties. They promoted the alcoholysis of epoxides [238], tetrahydropyranylation of alcohols [239], monothioacetahzation of acetals [240], and carbon-carbon bond formation of acetals [241,242] and imines [243] with silylated carbon nucleophiles. 

Some urea dissolved in anhydrous ethylene glycol, then finely divided tetracyanoethylene added, and heated ca. 15 min. at 70-75° on a steam bath with stirring until soln. is complete dicyanoketene ethylene acetal. Y 77-i F. e. s. C. L. Dickinson and L. R. Melby, Org. Synth. 39, 13 (1959). 

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