The first solid enols of anhydrides. Structure, properties, and enol/anhydride equilibria
The first solid enols of anhydrides. Structure, properties, and enol/anhydride equilibria
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DOI：
10.1021/jo071206m
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发表时间：
2007-11-23
影响因子：
3.6
通讯作者：
Rappoport, Zvi
中科院分区：
文献类型：
--
作者：
Song, Jinhua;Lei, Yi Xiong;Rappoport, Zvi
β-甲基戊二酸酐与NaOMe反应，然后与氯甲酸甲酯或氯甲酸苯酯反应，得到相应的O-甲氧基（和O-苯氧基）羰基化衍生物。酸酐与MgCl 2/吡啶反应，然后与氯甲酸甲酯反应，在酸酐的C3处产生C-甲氧基羰基化。产物（4）先前通过计算被认为是酸酐5的烯醇，并且这通过X射线晶体学（键长：C-OH，1.297埃; C1 C2 1.388埃; HO中心点中心点O=C（OMe）距离2.479埃）被证实，使其成为酸酐的第一固体烯醇。在CDCl 3、CD 3CN或C6 D 6溶液中，它显示OH作为约100 nm处的宽信号。15 ppm，表明与CO2 Me基团形成氢键。NICS计算表明4是非芳香族的。在CDCl 3中，当D2 O存在时，OH和C5 H质子都迅速地将H交换为D。在极性溶剂中与4平衡形成5的异构酸酐5a。在溶液中，随着CD 3CN百分比的增加，在CDCl 3：CD 3CN混合物中，快速建立了酸酐/烯醇平衡，其中K-烯醇为6.40（C6 D 6，298 K）、0.52（CD 3CN，298 K）、9.8（CDCl 3，298 K）、22.8（CDCl 3，240 K），并且Keno降低。在CDCl_3：（CD_3）（2）CO体系中，随着（CD_3）（2）CO含量的增加，重排酸酐所占的比例也随之增加。在DMSO_d（6）和DMF-d（7）体系中，观察到的主要是共轭碱4（-）和5a。测定氘对δ（C-13）值的影响。制备了被3-CO2 Me和4-OCO 2 Me基团取代的酸酐15的类似C2-OH烯醇。其结构通过X射线晶体学证实（CO键长1.298埃，O中心点中心点O中心点距离2.513埃）;在CDCl 3、THF-d（8）和CD 3CN中δ（OH）= 12.04-13.22 ppm，并且K-烯醇分别= >= 100、7.7和3.4。在DMSO-d（6）中，烯醇15电离成其共轭碱。在稀释烯醇溶液时，表观δ（“OH”）质子的显著高场位移归因于形成的H+与溶剂中的痕量水的相互作用，得到H3 O+，这给出了所谓的“OH质子”信号。
[Graphics]Reaction of beta-methylglutaeonic anhydride with NaOMe followed by reaction with methyl or phenyl chloroformate gave the corresponding O-methoxy (and O-phenoxy) carbonylation derivatives. Reaction of the anhydride with MgCl2/pyridine, followed by methyl chloroformate gave C-methoxycarbonylation at C3 of the anhydride. The product (4) was previously suggested by calculation to be the enol of the anhydride 5 and this is confirmed by X-ray crystallography (bond lengths: C-OH, 1.297 angstrom; C1C2 1.388 angstrom; HO center dot center dot center dot O=C(OMe) distance 2.479 angstrom) making it the first solid enol of an anhydride. In CDCl3, CD3CN, or C6D6 solution it displays the OH as a broad signal at ca. 15 ppm, suggesting a hydrogen bond with the CO2Me group. NICS calculations indicate that 4 is nonaromatic. With D2O in CDCl3 both the OH and the C5H protons exchange rapidly the H for D. An isomeric anhydride 5a of 5 is formed in equilibrium with 4 in polar solvents. In solution, anhydrides)/enol equilibria are rapidly established with K-enol of 6.40 (C6D6, 298 K), 0.52 (CD3CN, 298 K), 9.8 (CDCl3, 298 K), 22.8 (CDCl3, 240 K), and decreasing Keno, in CDCl3:CD3CN mixtures with the increase in percent of CD3CN. The percentage of the rearranged anhydride in CDCl3:(CD3)(2)CO increases with the increased percent of (CD3)(2)CO. In DMSOd(6) and DMF-d(7) the observed species are mainly the conjugated base 4(-) and 5a. Deuterium effects on the delta(C-13) values were determined. An analogous C2-OH enol of anhydride 15 substituted by 3-CO2Me and 4-OCO2Me groups was prepared. Its structure was confirmed by X-ray crystallography (CO bond length 1.298 angstrom, O center dot center dot center dot O distance 2.513 angstrom); delta(OH) = 12.04-13.22 ppm in CDCl3, THF-d(8), and CD3CN, and K-enol = >= 100, 7.7, and 3.4 respectively. In DMSO-d(6) enol 15 ionizes to its conjugate base. Substantial upfield shifts of the apparent delta("OH") proton on diluting the enol solutions are ascribed to the interaction of the H+ formed with the traces of water in the solvent to give H3O+, which gives the alleged "OH proton" signal.