The precise mechanism of the chiral phosphoric acid‐catalyzed aldol‐type reaction of azlactones with vinyl ethers was investigated. DFT calculations suggested that the reaction proceeds through a Conia‐ene‐type transition state consisting of the vinyl ether and the enol tautomer of the azlactone, in which the catalyst protonates the nitrogen atom of the azlactone to promote enol tautomerization. In
The enantioselective reaction of 2H-azirines with oxazol-5-(4H)-ones (oxazolones) using a cinchonaalkaloid sulfonamide catalyst has been developed. The reaction proceeded at the C-2 position of oxazolones to afford products with consecutive tetrasubstituted stereogenic centers in high yield with high diastereo- and enantioselectivity. The obtained aziridines were converted into various chiral compounds
Syn‐gled out: The syn diastereo‐ and enantioselective addition of azlactones to 3‐vinylindoles was accomplished by using a chiral, binapthol‐derived, Brønstedacid catalyst (see scheme). This method enables facileaccess to tryptophanderivatives with adjacent quaternary and tertiary stereogenic centers, which are potentially useful for the synthesis of peptidomimetics.
Enantioselective Construction of Consecutive Tetrasubstituted Stereogenic Centers by Reaction of α-Substituted β-Nitroacrylates with Oxazol-5-(4<i>H</i>)-ones Catalyzed by Cinchona Alkaloid Sulfonamide Catalysts
The enantioselective reaction of α-substituted β-nitroacrylates with oxazol-5-(4H)-ones (oxazolones) to construct consecutive tetrasubstituted stereogenic centers was accomplished. A cinchonaalkaloid sulfonamide catalyst afforded products bearing vicinal chiral centers with excellent enantio- and diastereoselectivities. The obtained products were successively converted into various chiral compounds
完成了α-取代的 β-硝基丙烯酸酯与 oxazol-5-(4 H )-ones (oxazolones) 的对映选择性反应,构建连续的四取代立体中心。金鸡纳生物碱磺酰胺催化剂为带有邻位手性中心的产物提供了出色的对映和非对映选择性。将所得产物连续转化为各种手性化合物而不损失其对映体纯度。此外,还进行了密度泛函理论 (DFT) 计算,以阐明观察到的反应立体选择性的机制和起源。
Enantioselective concomitant creation of vicinal quaternary stereogenic centers via cyclization of alkynols triggered addition of azlactones
作者:Zhi-Yong Han、Rui Guo、Pu-Sheng Wang、Dian-Feng Chen、Han Xiao、Liu-Zhu Gong
DOI:10.1016/j.tetlet.2011.08.123
日期:2011.11
An asymmetric cyclization of alkynols triggered addition of azlactones catalyzed by a combined catalyst system consisting of a chiral gold phosphate and a phosphoric acid produces conformationally restricted amino acid precursors bearing vicinal quaternary stereogenic centers in high levels of stereoselectivity. (C) 2011 Elsevier Ltd. All rights reserved.