AgNTf<sub>2</sub>-Mediated Allylation with Allylsilanes at C3<i>a</i>-Position of Hexahydropyrroloindoles: Application to Total Syntheses of Amauromine Alkaloids
various allyl groups including the reverse prenyl group. The utility of this reaction is demonstrated by total synthesis of amauromine alkaloids. Stepwise bromocyclizations of the bis-indolylmethyl diketopiperazine derivative and subsequent double reverse prenylation furnished (+)-novoamauromine and (−)-epiamauromine.
Kinetics of the reactions of allylsilanes, allylgermanes, and allylstannanes with carbenium ions
作者:Gisela Hagen、Herbert Mayr
DOI:10.1021/ja00013a035
日期:1991.6
isobutene/2k). A close analogy between the reactions of alkenes and allylelement compounds with carbeniumions is manifested, and the different reaction series are connected by well-behaved linear free energy relationships. The relative reactivities of terminal alkenes and allylelement compounds are almost independent of the electrophilicities of the reference carbeniumions (constant selectivity relationship)
<i>Z</i>-Selective Alkene Isomerization by High-Spin Cobalt(II) Complexes
作者:Chi Chen、Thomas R. Dugan、William W. Brennessel、Daniel J. Weix、Patrick L. Holland
DOI:10.1021/ja408238n
日期:2014.1.22
rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminateligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the
简单的末端烯烃异构化为具有 Z 立体化学的内部异构体的情况很少见,因为通常会形成更稳定的 E 异构体。我们在这里表明,由庞大的 β-二酮亚胺配体支撑的钴 (II) 催化剂具有适当的动力学选择性来催化一些简单的 1-烯烃的异构化,特别是作为稳定性较差的 Z-异构体的 2-烯烃。催化通过“烷基”机制进行,三配位钴 (II) 烷基配合物作为静止状态。如同位素标记实验所示,β-氢化物消除和 [1,2]-插入步骤都很快。立体模型通过在 β-氢化物消除的过渡态钴 (II) 处的方形平面几何结构来解释选择性。该催化剂不仅适用于简单的烯烃,还适用于高烯丙基硅烷、缩酮、和甲硅烷基醚。从与不良底物的反应中分离出钴 (I) 或钴 (II) 产物表明,关键的催化剂分解途径是双分子的,降低催化剂浓度通常会提高选择性。除了潜在有用的选择性转化之外,这些研究还为高自旋钴配合物催化烯烃异构化提供了机理理解,并证明了空间体
A class of compounds useful in pharmaceutical compositions and methods for treating or preventing cancer is described. Analogs of Mycalolide B have been prepared and tested in breast and ovarian cancer cell lines. The compounds show utility for inhibition of survival and proliferation of tumor cells. The compounds have been shown to disrupt actin.
Several macrocyclization reaction attempts of highly advanced precursors toward a total synthesis of marine diterpene bielschowskysin are disclosed. Biomimetic [2+2]-photocyclization reactions were applied to construct the cyclobutane core in these intermediates, which could be accessed along scalable high-yielding reaction sequences from cheap enantiopure starting-materials.