Aminolysis of Y-Substituted Phenyl Diphenylphosphinates and Benzoates:Effect of Modification of Electrophilic Center from C=O to P=O

摘要

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 (la) with alicyclic secondary amines resulted in a linear Bronsted-type plot with a beta_(nuc) value of 0.38,while the corresponding reactions of 2,4-dinitrophenyl benzoate (2a) yielded a curved Bronsted-type plot.Similarly,a linear Bronsted-type plot with a beta_(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 Bronsted-type plot.The linear Bronsted-type plots for the reactions of 1a-j have been taken as evidence for a concerted mechanism,while the curved Bronsted-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 sigma~-constants (R~2=0.962) but slightly better correlation with sigma~(deg) (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 beta_(nuc) and small r values.