Kinetics and mechanism of the addition of benzylamines to benzylidene-3,5-heptadione in acetonitrile.
The addition reaction of benzylamine (XC6H4CH2NH2) to benzylidene-3,5-heptadione (BHD; YC6H(4-)CH=C(COEt)(2)) in acetonitrile is investigated. The rate is slower than the corresponding rate for benzylidenediethylmalonate (YC6H4CH=C(OOEt)(2)) as the result of a greater steric hindrance in the planar dicarbonyl transition state. The kinetic isotope effects (k(H)/k(D)) involving deuterated amine nucleophiles (XC6H4CH2ND2) are greater than 1 (1.37-2.04), indicating N-H bond stretching with concurrent N-C(alpha) and H-C(beta) bond formation in the TS. The trend of change in k(H)/k(D) with variation of substituent X in the nucleophile conforms to the Bell-Evans-Polanyi principle. It has been stressed that the dicarbonyl group activated olefins exhibit insignificant charge imbalance in the TS for the benzylamine additions in acetonitrile as a result of the two strong n(c) --> pi*(C=O) vicinal charge-transfer interactions.
Oh
Hyuck Keun
HK
Department of Chemistry, Chonbuk National University, Chonju 560-756, Korea.
Lee
Jae Myon
JM
Sung
Dae Dong
DD
Lee
Ikchoon
I