Preparation and reactivity of persistent and stable silyl-substituted bisketenes

Article abstract of DOI:10.1021/ja00075a027

2,3-Bis(trimethylsilyl)-1,3-butadiene-1,4-dione (1) is formed as the only product on thermolysis of 3,4-bis(trimethylsilyl)cyclobut-3-ene-1,2-dione (2), and the rate of ring opening of 2 is comparable to that of substituted cyclobutenes and cyclobutenones. Photolysis of 2 also forms 1, which reacts with ethanol in a stepwise fashion with faster addition of one ethanol molecule to give an isolable monoketene 18, which reacts in a further slower step to give succinate diesters, accompanied by desilylation. 2,3-Bis(tert-butyldimethylsilyl)-1,3-butadiene-1,4-dione (3), prepared analogously to 1, similarly adds one molecule of methanol to give the isolable monoketene 20, which then reacts to give dimethyl 2,3-bis(tert-butyldimethylsilyl)succinate (21) as the major product. The reaction of 1 with H₂O is faster than with alcohols and forms (E)- and (Z)-2,3-bis(trimethylsilyl)succinic anhydrides (13) as the first observed products. The reactivity of 1 with different nucleophilic solvents is correlated by the Winstein-Grunwald equation and increases with both solvent ionizing power and solvent nucleophilicity.