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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 3
BKCSDE 33(3)
March 20, 2012 

 
Title
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
Author
Hasi Rani Barai, Hai Whang Lee*
Keywords
Phosphoryl transfer reaction, Anilinolysis, (2R,4R,5S)-(+)-2-Chloro-3,4-dimethyl-5-phenyl- 1,3,2-oxazaphospholidine 2-sulfide, Deuterium kinetic isotope effect
Abstract
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 (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at 5.0 oC. The anilinolysis rate of 3 involving a cyclic five-membered ring is considerably fast because of small negative value of the entropy of activation (ΔS≠ = –2 cal mol–1 K–1) over considerably unfavorable enthalpy of activation (ΔH≠ = 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 SN2 mechanism with a backside nucleophilic attack is proposed on the basis of the secondary inverse deuterium kinetic isotope effects, kH/kD < 1.
Page
1037 - 1041
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