The title compound is obtained by reacting u-cyano-4-nitrostyrene-p-ol with dicyclohexylcarbodiimide (molar ratio 21) at room temperature in tetrahydrofuran solvent.
Esters of a-cyano-4-nitrostyrene-p-ol (1; HOCs(p-NO2)) are powerful acylating agents (1, 2). In the initial stage of our work in this field we had reacted Z-Val-OCs(p-N02) with CIVal-OMe/Et3N to yield the crystalline Z-Val-Val-OMe. Thin layer chromatography of the mother liquor disclosed the presence of a yellow spot, which we guessed to be bis(u-cyano-4-nitrostyrene-p-yl) ether (2; O[Cs(p-NO2)I2). This notion gained credibility when in a CDC13 solution of Et3N and a-cyano-4-nitrostyrene-p-yl acetate (3; AcOCs(p-N02)) not only the "yellow spot" (TLC analysis), but also acetic anhydride was detected ( l H NMR analysis). Would we
Structural Formulas have hit upon an unprecedented reaction, the dismutation of an ester into an anhydride and an ether? The answer is no, because it soon became clear in the first place that the acetic anhydride is quite unexceptionally generated from the reaction of 3 and acetic acid (the latter formed by some hydrolysis of 3 ) and in the second place that the "yellow spot"is simply the triethylammoniumsalt of 1 (Schemel). SCHEME 1