Kinetics and Mechanism of the Anilinolysis of (2R,4R,5S)-(+)-2-Chloro-3,4-dimethyl -5-phenyl-1,3,2-oxazaphospholidine 2-Sulfide in Acetonitrile

• Published in: Bulletin of the Korean Chemical Society Vol. 33; no. 3; pp. 1037 - 1041
• Main Authors: Barai, Hasi Rani, Lee, Hai-Whang
• Format: Journal Article
• Language: Korean
• Published: 2012
• Subjects: Phosphoryl transfer reaction; (2R,4R,5S)-(+)-2-Chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide; Deuterium kinetic isotope effect; Anilinolysis
• ISSN: 0253-2964; 1229-5949

The nucleophilic substitution reactions of (2R,4R,5S)-(+)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $5.0^{\circ}C$. The anilinolysis rate of 3 involving a cyclic five-membered ring is considerably fast because of small negative value of the entropy of activation (${\Delta}S^\neq=-2cal\;mol^{-1}\;K^{-1}$) over considerably unfavorable enthalpy of activation (${\Delta}H^\neq=18.0\;kcal\;mol^{-1}$). Great enthalpy and small negative entropy of activation are ascribed to sterically congested transition state (TS) and bulk solvent structure breaking in the TS. A concerted $S_N2$ mechanism with a backside nucleophilic attack is proposed on the basis of the secondary inverse deuterium kinetic isotope effects, $k_H/k_D$ < 1.