Dicyanoketene acetals

Copolymeriziation of polystyrene-bound dicyanoketene acetal (DCKA) and ethylene glycol dimethacrylate (EGDMA) yielded a polymer (41) with high n -acidity. It was found to be an effective and completely recyclable catalyst in the high yielding carbon-carbon bond-forming reaction of dimethylacetals with silylated nucleophiles (Scheme 4.26) [118]. 

Scheme 4.26 Polystyrene-bound dicyanoketen acetal - solid with high r-acidity for the activation of acetals.

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. 

Dicyanoketene ethylene acetal reacts with tertiary amines to give quaternary ammonium inner salts.3 Similarly, it reacts with sulfides to give sulfonium inner salts.3 These products are generally solids that can be used to characterize tertiary amines, and sulfides. Dicyanoketene acetals can be converted to pyrimidines, pyrazoles, or isoxazoles in one step.4... 

Polymer supported dicyanoketene acetal, CH3CN, H2O, rt, 2h, 73-96% yield. This reagent also cleaves dioxolanes and THP and TBS ethers. ... 

Monothioacetalization. One alkoxy group of an acetal can be replaced by a thio group using RSH or RSSiMej when catalyzed by a dicyanoketene acetal or tetra-cyanoethylene. 

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