Aminolysis of Y-substituted phenyl diphenylphosphinates and benzoates: Effect of modification of electrophilic center from C=O to P=O

Abstract

(Chemical Equation Presented) The effect of modification of the electrophilic center from C=O to P=O on reactivity and reaction mechanism has been investigated for aminolysis of Y-substituted phenyl diphenylphosphinates (1a-j) and benzoates (2a-i). The phosphinates 1a-j are less reactive than the benzoates 2a-i. The reactions of 2,4-dinitrophenyl diphenylphosphinate (1a) with alicyclic secondary amines resulted in a linear Brønsted-type plot with a β nuc value of 0.38, while the corresponding reactions of 2,4-dinitrophenyl benzoate (2a) yielded a curved Brønsted-type plot. Similarly, a linear Brønsted-type plot with a β 1g value of -0.66 was obtained for the reactions of 1a-j with piperidine, while the corresponding reactions of 2a-i gave a curved Brønsted-type plot. The linear Brønsted-type plots for the reactions of 1a-j have been taken as evidence for a concerted mechanism, while the curved Brønsted-type plots for the reactions of 2a-i have been suggested to indicate a change in the rate-determining step of a stepwise mechanism. The Hammett plot for the reactions of 1b-j exhibited a poor correlation with σ - constants (R 2 = 0.962) but slightly better correlation with σ o (R 2 = 0.986). However, the Yukawa-Tsuno plot for the same reactions resulted in an excellent correlation (R 2 = 0.9993) with an r value of 0.30. The aminolysis of 1a-j has been suggested to proceed through a concerted mechanism with an early transition state on the basis of the small β nuc and small r values. © 2006 American Chemical Society.