Journal of Organic Chemistry p. 4509 - 4513 (1983)
Update date:2022-08-11
Topics:
Kwart, Harold
Gaffney, Anne
Wilk, Kazimiera A.
Amine bases show reaction rates and activation parameters that suggest close similarity to the E2C mechanism previously identified for the Br(1-)-promoted reaction with α-bromo ester.Proton Sponge (PS), an amine base, which cannot participate in an SN2 process, nonetheless, is an effective promoter of the E2C.This is confirmed by applying the temperature-dependent isotope effect (TDKIE) criteria of transition-state geometry to PS and other amine reactions with α-bromo esters with the general result that <ΔEa>DH is found to be temperature independent and AH/AD >> 1.2.The α-secondary deuterium isotope effect, (kH/kD)α = 1.27, is the largest value ever found (thus far) for either SN2-like or β-elimination processes.On these and other grounds it is concluded that the E2C mechanism is not SN2 like but is regarded as a precedented nucleophilic trigger mechanism.The virtual identity of intra- and intermolecular isotope effects among amine base promoters cannot be explained by the formation of a symmetrical trigonal-bipyramid (TBP) intermediate, as was the case for the Br(1-)-promoted reaction with α-bromo ester substrates.But the obviously equal availability of abstractable H and D in the transition states of the intramolecular competition isotope effect is possibly to be explained by invoking permutational isomerism in the precursor trigonal-bipyramid (TBP) intermediate.The reasoning which seems to justify this proposal is considered in detail.
View MoreContact:86 21 3772 9386
Address:Rm.1803,Starry Bldg.1,1505 Meijiabang Road,Shanghai 201620 China
TAIZHOU XINGCHENG CHEMPHARM CO.,LTD.
Contact:0086-0576-88551200,88886292 ,88880039
Address:B Area. 10 Floor.Yaodadasha. 289#.Shifu Road.Taizhou.Zhejiang.China
Shanghai Dianyang Industry Co.,ltd
Contact:+86 21 6492 4669
Address:Chejing RD, Songjiang District, Shanghai, China
Tianjin Crest Pharmaceutical R&D Co., Ltd. (Tianjin Yao Technology Development Co., Ltd.)
Contact:+86-22-66211386
Address:Building B5-405, No, 80 4th Avenue, TEDA, Tianjin, China P.R. 300457
GUANGZHOU MEDCAN PHARMATECH LTD
website:http://www.gzmedcan.com
Contact:+86-20-82519649
Address:Building J,Room 101,1 JiangtashanRd,Guang Zhou Science City,Guang Zhou ,China
Doi:10.1016/0009-2614(88)87353-6
(1988)Doi:10.1002/bbpc.198800198
(1988)Doi:10.1111/cbdd.13176
(2018)Doi:10.1021/jp805002a
(2008)Doi:10.1016/j.tet.2004.08.013
(2004)Doi:10.1039/c7ob03067c
(2018)