Total Synthesis of (−)-Colchicine by an Oxyallyl [4+3] Cycloaddition
作者:Jae Chol Lee、Jin Kun Cha
DOI:10.1016/s0040-4020(00)00862-0
日期:2000.12
An enantioselective synthesis of (−)-colchicine, free from isocolchicine, is delineated and features tandem application of the intramolecular Diels–Alder reaction of acetylene-tethered oxazoles and the [4+3] cycloaddition of oxyallyls. This work underscores the synthetic utility of little explored α-alkoxy substituted oxyallyls.
Total Synthesis of Tropoloisoquinolines: Imerubrine, Isoimerubrine, and Grandirubrine<sup>1</sup>
作者:Jae Chol Lee、Jin Kun Cha
DOI:10.1021/ja0101072
日期:2001.4.1
ready access to the tropoloisoquinoline alkaloids imerubrine (1), grandirubrine (2), and isoimerubrine (3) is delineated and features sequential application of the intramolecular Diels-Alder reaction of an acetylene-tethered oxazole and the [4 + 3] cycloaddition of an oxyallyl. A regioselective synthesis of 1 was achieved by stereo- and regioselective oxidation of an 8-oxabicyclo[3.2.1]oct-6-en-3-one cycloadduct
aromatic aldehydes and silyl enol ethers in benzene as the solvent. The reactions occur with high simple diastereoselectivity and, when R¹ is chiral, with high facial diastereoselectivity. Under similar conditions, but in acetonitrile rather than benzene as the preferred solvent, the Paternò-Büchi reaction of N-acylenamines (enamides) gives the corresponding protected 3-aminooxetanes. The cis-products
Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis
作者:Steven M. Banik、Anna Levina、Alan M. Hyde、Eric N. Jacobsen
DOI:10.1126/science.aao5894
日期:2017.11.10
used this motif to activate a Lewis acid cocatalyst, pulling a leaving group off silicon instead of carbon (see the Perspective by Mattson). The combined pair of catalysts is more effective for reactions such as asymmetric cycloadditions that involve weaker leaving groups on carbon. Science, this issue p. 761; see also p. 720 A chiral amide activates a silicon-based Lewis acid for joint asymmetric catalysis
路易斯酸催化由标记团队攻克具有两个紧密间隔的氮氢基团的分子催化剂可以像镊子一样发挥作用,通过双氢键锁定离去基团,然后将其拉开,从而激活碳中心。在所得离子对中,催化剂的形状可以使随后的反应偏向于仅有利于两种可能的镜像产物中的一种。巴尼克等人。使用这个主题来激活路易斯酸助催化剂,从硅而不是碳上拉出离去基团(参见 Mattson 的观点)。组合的催化剂对对于涉及碳上较弱离去基团的不对称环加成等反应更有效。科学,本期第 14 页。第761章另见 p. 720 手性酰胺可激活硅基路易斯酸以进行联合不对称催化。小分子双氢键(H键)供体,如脲、硫脲、方酰胺和胍离子,作为促进各种对映选择性反应的有效催化剂而得到广泛应用。然而,这些催化剂仅呈弱酸性,因此需要高反应性的亲电子底物才能有效。我们在这里介绍了一种手性氢键供体的催化活性模式,该模式能够使相对不活泼的亲电子试剂发生对映选择性反应。方酰胺与三氟甲磺酸硅
Stereo- and regiocontrolled hydroxylation of oxyallyl [4+3] cycloadducts. A concise synthesis of hinokitiol
作者:Jae Chol Lee、Sung Yun Cho、Jin Kun Cha
DOI:10.1016/s0040-4039(99)01589-0
日期:1999.10
Stereo- and regioselective hydroxylation of 8-oxabicyclo[3.2.1]oct-6-en-3-ones was achieved by the action of (diacetoxyiodo)benzene in methanolic potassium hydroxide (the Moriarty oxidation). Subsequent double elimination afforded a convenient preparation of substituted tropolones, as exemplified in a three-step synthesis of hinokitiol (1).