已经将两种羧酸的烯醇化酮化,即2,2-双(2,4,6-三甲基苯基)乙烯-1,1-二醇2a和2,2-双(五甲基苯基)乙烯-1,1-二醇2b。在25°C的1∶1乙腈水中进行了研究。这些化合物的稳定性来自β-碳位点质子化的抑制作用,这种作用现已被量化。据报道,对于(Mes)2 C C(OH)2 2a的第一个羟基的电离,p K a为8.18 ,对于(PMP)2 C C(OH)2 2b的p K a为8.63 。已经确定了两种物种在整个pH范围内的pH速率曲线。检测到一般的酸催化作用,产生布朗斯台德(Brønsted)α2a和2b的值分别为0.35和0.34。类似地,对于两种烯醇式单阴离子的一般酸催化计算得出的布朗斯台德α'值分别为0.48和0.45。对相应甲酯的烯醇的酮化的研究已经允许对羧酸,酯和乙烯酮缩醛的烯醇的反应性进行比较研究。Mes 2 C C(OH)(OCH 3)的反应性与烯醇Mes 2 C
The first acid and ester enols: 2,2-bis(pentamethylphenyl)ethene-1,1-diol and 1-t-butoxy-2,2-bis(pentamethylphenyl)ethenol, and their oxidation to stable free radicals
作者:Patrick O'Neill、Anthony F. Hegarty
DOI:10.1039/c39870000744
日期:——
Desilylation of the ketene acetals (5) and (9) provides the ene-1,1-diols (6) and (10) which undergo relatively slow ketonisation and are oxidized to stablefreeradicals in basic solution.
Relatively stable N-benzhydryl- and N-benzyldiarylketene imines and their conversion to cyanodiarylmethanes via an isolable radical
作者:Leo F. Clarke、Anthony F. Hegarty、Pat O'Neill
DOI:10.1021/jo00027a062
日期:1992.1
An efficient synthetic route to the sterically hindered ketene imines N-benzyl- and N-benzylhydrylbis(pentamethylphenyl)ketene imines 8 from dipentamethylphenyl ketene 6 is described. The thermal stability of these ketene imines is in marked contrast to the diphenylketene imine analogues which rearrange rapidly to C-tri-substituted nitriles. On heating 8b is converted to the relatively stable free radical 13 which can be reduced to the nitrile 10 in a variety of solvents. These radicals are proposed intermediates in the ketene imine-nitrile rearrangement, and the mechanism of this reaction is considered in in terms of these results.
Regiospecific reactions of the ambident anion of bis(pentamethylphenyl)acetonitrile
作者:Leo F. Clarke、Anthony F. Hegarty
DOI:10.1021/jo00032a064
日期:1992.3
Hydration of bis(pentamethylphenyl)- and bismesityl-ketenes leading to ene-1,1-diols (enols of carboxylic acids)
作者:Barbara M. Allen、Anthony F. Hegarty、Pat O'Neill、Minh Tho Nguyen
DOI:10.1039/p29920000927
日期:——
The reaction of the sterically hindered diarylketenes (Ar = Me5C6 or 2,4,6-Me3C2H2) with water is pH independent over the range 1-9 and is not subject to strong buffer catalysis. The primary products formed are the corresponding ene-1,1-diols which result from addition across the C=O (rather than the C=C) of the ketene. These `enols of carboxylic acids' are relatively long lived owing to slow protonation of the beta-carbon (because of steric hindrance caused by the o-Me groups) and evidence for their structures in solution is presented. On attempted isolation of the ene-l,l -diols facile oxidation to a stable free radical, as well as ketonisation to the corresponding acids, occurs. Evidence is presented in terms of the large negative entropy of activation (ca. 200 J K-1 mol-1), solvent isotope effects and the absence of significant general-base catalysis, that (despite the sterically hindered nature of these ketenes) the characteristics of their hydration are typical of other ketenes and that this most likely involves an initial concerted reaction with a water oligomer. Updated ab initio calculations are also presented, which are consistent with this view.
Eventova, Irina; Nadler, Ella B.; Rochlin, Elimelech, Journal of the American Chemical Society, 1993, vol. 115, # 4, p. 1290 - 1302
作者:Eventova, Irina、Nadler, Ella B.、Rochlin, Elimelech、Frey, Joseph、Rappoport, Zvi