Unexpected Cycloisomerizations of Nonclassical Carbocation Intermediates in Gold(I)-Catalyzed Homo-Rautenstrauch Cyclizations
摘要:
An unexpected gold(I)-catalyzed homo-Rautenstrauch rearrangement of 1-cyclopropyl propargylic esters to cyclohexenones is disclosed. This rearrangement represents new evidence for the recently discussed gold-stabilized non-classical carbocation character of intermediates in gold catalysis. A mechanistic study proved partial chirality transfer from optically active propargyl acetates.
Enantioselective Total Synthesis of atrans-Hydrindane Rings/Side-Chain Building-Block of Vitamin D− Asymmetric Induction in an Acid-Catalyzed Conjugate-Addition Reaction
For the enantioselective total synthesis of 1α,25-dihydroxyvitamin D3 (3), we have developed an enantioselective approach to the “northern” portion building-block 8, starting from the optically active hexanoic acid derivative 44, 2-methylcyclopent-2-en-1-one (10) and 1-(phenylthio)but-3-en-2-one (9). The steric course of the addition reaction of homochiral (S)-ketene acetals 28, 40, 44 and 58 with
Readily available from esters or ketones, cyclopropanols are inclined to undergo diverse ring-opening transformations. Their one-electron oxidation is a conventional way to β-carbonyl radicals. However, despite this fact, their application as a coupling partner in dual photoredox and nickel-catalyzed reactions with organic halides remains underdeveloped. Here, we report that the Ti(OiPr)4 additive
环丙醇很容易从酯或酮中获得,倾向于进行各种开环转化。它们的单电子氧化是β-羰基自由基的常规方式。然而,尽管如此,它们作为偶联伙伴在与有机卤化物的双重光氧化还原和镍催化反应中的应用仍然不成熟。在这里,我们报告了 Ti(O i Pr) 4添加剂使这种难以捉摸的与芳基溴和烯基溴的交叉偶联成为可能,从而产生 β 取代的酮。
Asymmetric Catalysis on the Intramolecular Cyclopropanation of α-Diazo-β-keto Sulfones
analysis, and the outcome of the enantioselectivities is explained well by our proposed models A and B. The products possess great potential for natural product synthesis because (1) many different chemistries of cyclopropane, ketone, and sulfone are available, and (2) the products are generally highly crystalline, facilitating the supplies of enantiomerically pure synthetic intermediates.
这项工作描述了对 α-重氮-β-酮砜的分子内环丙烷化的高度对映选择性不对称催化的发展。我们发现,当 α-重氮-β-酮基甲基砜与新制备的配体 2e 一起使用时,α-重氮-β-酮基砜的催化不对称分子内反应通常以高对映选择性进行。产品的绝对构型已通过 X 射线晶体学分析确定,我们提出的模型 A 和 B 很好地解释了对映选择性的结果。这些产品具有天然产物合成的巨大潜力,因为 (1) 环丙烷的许多不同化学性质、酮、砜都有,(2)产物一般是高度结晶的,
Controlling 6-endo-selectivity in oxidation/bromocyclization cascades for synthesis of aplysiapyranoids and other 2,2,6,6-substituted tetrahydropyrans
alkoxy substituent anti-selectively across the doublebond, indicating a bromonium ion-mechanism for the ring closure. 6-endo-control of the alkenol cyclization thereby arises from the polar effect of the aryl substituent. Two methyl substituents bound to the alkene terminus are not similarly able to favor 6-endo-cyclization, because strain arising from methyl group repulsion, as the bromonium-activated