structure. (3) The reactions show characteristic positional effects of substitution on the benzene ring. While an electron-withdrawing group such as CF3 at C5, C6, or C7 positions decelerates the reaction, the same substituent at C8 accelerates the reaction, compared with the reaction of unsubstituted 4H-1,2-benzoxazine. In particular, substitution at C5 significantly decelerates the reaction as compared
在这里,我们描述了在苯环上带有各种取代基的4 H -1,2-苯并恶嗪的逆Diels-Alder反应的机理研究。4 H -1,2-苯并恶嗪是非常简单的化合物,但是是相当新的杂环化合物,可在温和的热条件下通过逆狄尔斯-阿尔德反应提供取代的邻醌甲基化物(o -QM)。生成的o -QM与亲二烯体原位进行Diels-Alder反应,得到苯酚和苯并二氢吡喃衍生物。对o -QMs的生成机理的研究很少。我们的实验和密度泛函理论(DFT)研究得出了以下结果。(1)o的生成-QMs,即4 H -1,2-苯并恶嗪的反杂Diels-Alder反应,是决定速率的,而不是随后的邻-QM与亲二烯体的Diels-Alder反应。(2)反应速度受取代基的电子特征和溶剂极性的强烈影响。反应可能在极性溶剂(例如二甲基亚砜)中进行得更快,这可能是因为电子极化的TS结构稳定了。(3)反应显示出取代在苯环上的特征性位置效应。虽然在C
Diastereo- and Enantioselective Synthesis of Quaternary α-Amino Acid Precursors by Copper-Catalyzed Propargylation
A diastereo- and enantioselective propargylic substitution reaction between propargylic carbonates and α-substituted nitroacetates catalyzed by a Cu-pybox complex is described. This method allows the preparation of a series of non-proteinogenic quaternary α-aminoacid precursors featuring two contiguous stereogenic centers and a terminal alkyne moiety in high yields with good to excellent diastereo-
A Facile Synthesis of α-Amino Esters via Reduction of α-Nitro Esters Using Ammonium Formate as a Catalytic Hydrogen Transfer Agent
作者:Siya Ram、Richard E. Ehrenkaufer
DOI:10.1055/s-1986-31497
日期:——
Various nitroesters 3 were selectively and rapidly reduced to their corresponding amino esters 4 in very good yield using anhydrous ammonium formate as a catalytic hydrogen transfer agent.
Enantioselective Synthesis of Quaternary α-Amino Acids Enabled by the Versatility of the Phenylselenonyl Group
作者:Antonin Clemenceau、Qian Wang、Jieping Zhu
DOI:10.1002/chem.201604781
日期:2016.12.19
conjugate addition of α‐alkyl substituted α‐nitroacetates to phenyl vinyl selenone was developed. The resulting enantio‐enriched α,α‐dialkyl substituted α‐nitroacetates were subsequently converted to various cyclic and acyclic quaternary α‐amino acids, taking advantage of the rich functionalities of the resulting Michael adducts. Novel protocols allowing chemoselective reduction of phenyl selenone to
4<i>H</i>-1,2-Benzoxazines with Electron-Withdrawing Substituents on the Benzene Ring: Synthesis and Application as Potent Intermediates for Oxygen-Functionalized Aromatic Compounds
4H-1,2-benzoxazine rings functionalized with various electron-withdrawingsubstituents on the benzene ring. Furthermore, we also show that the resulting 4H-1,2-benzoxazines can be used as precursors of functionalized o-quinone methides and multisubstituted phenols. This type of heterocycle can be a potent intermediate to oxygen-fuctionalized aromatic compounds.