[3716-97-0] · C6H4N2 · 1,2-Dicyanocyclobutene · (MW 104.11)
(reactive dienophile in [4 + 2],1 [3 + 2],2 and [2 + 2]3 Diels-Alder additions; reactive diene in [4 + 2] inverse electron demand Diels-Alder additions upon in situ thermolytic cleavage to 2,3-dicyanobutadiene)
Alternate Name: cyclobutene-1,2-dicarbonitrile.
Physical Data: bp 58-60 °C/0.06 mmHg; n
Solubility: insol H2O; sol most organic solvents.
Form Supplied in: colorless liquid; not commercially available.
Preparative Methods: may be prepared by several methods.4 The most convenient involves the chlorination of 1,2-dicyanocyclobutane with Phosphorus(V) Chloride followed by dechlorination with Triethylamine in refluxing benzene to give the reagent in good yield1,5 (eq 1).
Purification: prepared by the method described, the reagent may be used directly for most cycloadditions. To remove trace impurities (1-4%) and obtain the pure compound, stir for 4 h over Raney cobalt under N2 at 70 °C, then distill directly under vacuum; purity may be assessed by gas chromatography.5
1,2-Dicyanocyclobutene (1) functions as a reactive dienophile in [4 + 2] cycloadditions to numerous diene systems. Endo versus exo selectivity is dependent on the presence of sp3 carbon atoms in the diene (eqs 2-4).1 The reactions are generally run without solvent.
1,2-Dicyanocyclobutene is easily converted to 2,3-dicyanobutadiene (eq 5). Thermolytic cleavage in situ generates the diene which undergoes inverse electron demand Diels-Alder cycloaddition to a number of dienophiles.1,5 The in situ generation procedure has the advantage of avoiding the tendency of the diene to polymerize in the pure state (eqs 6-8).
1,2-Dicyanocyclobutene also undergoes [3 + 2] cycloadditions with diazomethane and ethyl diazoacetate (eq 9).2,3 Yields were not reported.
Photocatalyzed [2 + 2] cycloadditions of 1,2-dicyanocyclobutene with various alkenes have been demonstrated.3 The reagent is strongly absorbent at 234 nm in acetonitrile, and the high degree of ring strain allows it react where other alkenes do not. Yields are moderate (eq 10).
Richard T. Beresis & James S. Panek
Boston University, MA, USA