C-Azidodiazirines in the SRN1 reaction of azide ion with arylchlorodiazirines. Further insights into reaction mechanism
摘要:
Mixtures of arylchlorodiazirines and sodium azide in DMSO form visible charge transfer complexes. Irradiation of these solutions with fluorescent room light leads to S(RN)1 displacement of chloride and the transient formation of C-azidodiazirines. Relative reactivity studies (using competition experiments) show that nitro-substituted arylchlorodiazirines are substantially more reactive than other arylchlorodiazirines. This is attributed to facile electron transfer in the propagation cycle, involving the nitro-substituted aromatic ring. C-Azidodiazirines can be isolated in solution and spectroscopically characterized when the S(RN)1 reaction is initiated by addition of catalytic amounts of the sodium salt of 2-nitropropane. These azidodiazirines readily decompose at room temperature by first order processes to give molecular nitrogen and benzonitriles. Solvent and substituent effects on decomposition rates are minimal. Computational studies on potential intermediate carbenes in the decomposition of azidodiazirines have been carried out at the HF/6-31G* level. Singlet alpha-azidocarbenes RCN3, where R = NH2, OH, F, vinyl, phenyl, and CH3, are energy minima at this computational level. Isodesmic calculations show that the azido group is comparable to OH in its carbene stabilizing ability. Subsequent loss of N2 from alpha-azidocarbenes, leading to nitriles, is a highly exothermic process (126 kcal when R = vinyl and 128 kcal when R = phenyl).
Hammett Analysis of a Family of Carbene−Carbene Complex Equilibria
作者:Lei Wang、Robert A. Moss、Jack Thompson、Karsten Krogh-Jespersen
DOI:10.1021/ol200083a
日期:2011.3.4
p-X-substituted phenylchlorocarbenes (X = NO2, CF3, Cl, H, Me, and MeO) form π-type complexes with trimethoxybenzene in pentane. The carbenes and complexes are in equilibrium, and logarithms of the measured equilibrium constants are well correlated by Hammett σp constants with ρ = 2.48. The carbene complexes are characterized by UV−vis spectroscopy, and computational analysis is afforded by DFT calculations
p -X取代的苯基氯卡宾(X = NO 2,CF 3,Cl,H,Me和MeO)与戊烷中的三甲氧基苯形成π型络合物。卡宾和配合物处于平衡状态,测得的平衡常数的对数与Hammettσp常数(ρ= 2.48)具有很好的相关性。卡宾配合物的特征在于紫外可见光谱,DFT计算提供了计算分析。
Hammett analysis of absolute carbene addition rate constants
Absoluterateconstants were determined for the additions of 5 5-X-substituted ArCCl (X=CF3, Cl, H, CH3, CH3O) to tetramethylethylene, trimethylethylene, trans-pentene, and 1-hexene; good Hammett correlations were obtained with ϱ = +1.4 – 1.6.
reactions of phenylchlorocarbene and related carbenes with alkenes are summarized and systematized. The experiments described provide the basis for a detailed examination of carbenic reactivity-selectivity principles. The results of studies on the influence of temperature on the absolute rate constants for carbene reactions are consistent with the existence of transient carbene/alkene intermediates.
Addition of arylchlorocarbenes to .alpha.,.beta.-unsaturated esters. Absolute rates, substituent effects, and variable reactivities
作者:N. Soundararajan、Matthew S. Platz、James E. Jackson、Michael P. Doyle、Su Min. Oon、Michael T. H. Liu、Surinder M. Anand
DOI:10.1021/ja00229a031
日期:1988.10
La reaction des (aryl chloro) methylenes avec le maleate de diethyle produit des (aryl-3 chloro-3)cyclopropanedicarboxylates-1,2 de diethyle
La 反应 des (aryl chloro) methylenes avec lemaleate de diethyle produit des (aryl-3 chloro-3)cyclopropanedicarboxylates-1,2 de diethyle
Kinetics and spectroscopy of ylids from reaction of p-substituted phenylchlorocarbenes with acetone
作者:N Soundararajan、James E Jackson、Matthew S Platz、Michael T.H Liu
DOI:10.1016/0040-4039(88)85178-5
日期:1988.1
Laser flashphotolysis of p-CF3 and p-Cl-phenylchloro diazirines produces the corresponding carbenes which react with acetone to produce easily detected ylids. The absolute rate constants of reaction of these carbenes with acetone, and the rate constants of reaction of the ylids with diethylfumarate have been determined. No reaction was found between these carbenes and simple esters or ethylene carbonate