Journal of Organic Chemistry p. 4841 - 4846 (1982)
Update date:2022-08-02
Topics: Fragmentation Kinetic Demonstration Syn Effect β-Hydroxy Nitrosamine
Loeppky, Richard N.
Hazlitt, Lonnie G.
The base-induced fragmentation rate of β-hydroxy nitrosamines is subject to striking control by the stereochemical orientation of the N-nitroso function. (Z)-(2-Hydroxy-2,2-diphenylethyl)methylnitrosamine (1Z) is cleaved to dimethylnitrosamine and benzophenone (kobsd = 6.8x10-3 s-1) 287 times more rapidly than an equilibrium mixture of the Z and E isomers (13:87) at 35 deg C in tert-butyl alcohol containing potassium tert-butoxide.The rate constant for the fragmentation of the equilibrium mixture (kobsd = 2.37x10-5 s-1) is similar in magnitude to the rateconstant (kobsd = 1.67x10-5 s-1) for isomerization of the Z isomer (syn) to its E form.Arguments are presented in support of the hypothesis that the E isomer must isomerize prior to fragmentation.This remarkable stereoelectronic control of a C-C bond cleavage five bonds removed from the isomerizing N-NO group is attributed to the greater stability of the incipient syn α-nitrosamino carbanion.A Hammet study of substituent effects on the fragmentation rate of ring-substituted derivatives of 17 gives a ρ = -0.86, indicating modest positive charge development in the transition state.A detailed discussion of the mechanism is presented.
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Doi:10.1021/jo00148a033
(1982)Doi:10.1002/anie.201406577
(2014)Doi:10.1007/s11164-013-1529-x
(2015)Doi:10.1039/c9cc03893k
(2019)Doi:10.1021/jo501474w
(2014)Doi:10.1139/v82-309
(1982)