Investigation into the mechanism of lithiation of 2,3-dihydrooxepin
摘要:
The NMR characterization of the trienolate product of lithiation of 2,3-dihydrooxepin with 6-lithiodihydropyran in THF is reported. The NMR spectra also support a direct ring opening upon allylic lithiation via an E2-type mechanism rather than vinylic lithiation or stepwise allylic lithiation. We also found the structure of the trienolate product of this reaction to be the Z, Z configuration. (C) 2004 Elsevier Ltd. All rights reserved.
研究了乙醇,三氟乙醇和六氟丙-2-醇水溶液中溶剂组成对2-(对硝基苯氧基)四氢吡喃(1)的未催化水解速率常数和活化参数的影响,并研究了m(Y OTs)值是0.60。这个可观的但小于最大值的值是根据具有速率限制电离的S N 1机制进行的。α-氘的二次动力学同位素效应(α-kie)对1的未催化水解在水(46℃)中为1.17,在三氟乙醇水溶液(50%摩尔分数,70.6℃)中为1.15,在乙醇水溶液(50%摩尔分数,70.6℃)中为1.13。这些值对应于在25℃下约1.19,这是S N 1反应中限速电离的特征,并且明显高于酶催化的糖酵解的值。当1通过酸催化水解时,在含水酸性条件下(1.07,0.1mol dm -3盐酸,20.2℃),α-基较小。现已发现先前报道的在缓冲的二恶烷水溶液(1.063,25°C)中水解1的α-基对应于酸催化的水解。这些新结果为1这表明在25℃下α-基值小于约1.15的酶
Alkynyliodonium Salts in Organic Synthesis. Dihydrofuran Formation via a Formal Stevens Shift of a Carbon Substituent within a Disubstituted-Carbon Oxonium Ylide
作者:Ken S. Feldman、Michelle Laci Wrobleski
DOI:10.1021/jo0011080
日期:2000.12.1
and 1-pyranyl ethers of 1-hydroxybut-3-ynyl(phenyl)iodonium triflate triggers a sequence of reactions that ultimately delivers 2-substituted 3-p-toluenesulfonyldihydrofuran products in variable yields. A putative 1,2-group shift within an unsaturated oxonium ylide (Stevens rearrangement) accounts for the oxygen-to-carbon transfer of the ether substituent. Deuterium labeling studies clarify the mechanistic