A method for the stereoselective construction of 4-alkoxy-5-alkylidenecyclopentenones by the tandem ring expansion-functionalization of 1-alkynylcyclobutenols using a palladium-mercury cocatalytic system
摘要:
1-(1-Alkynyl)-4-methoxy-4-methyl-2-cyclobutenols, prepared by nucleophilic functionalization of cyclobutenediones, were transformed with high stereoselectivity into 4-methoxy-4-methyl-5-alkylidenecyclopentenones. The action of stoichiometric Hg(OCOCF3)(2) and then metathesis with NaCl produced 5-(1-(chloromercurio)alkylidene)-4-methoxy-4-methyl-2-cyclopentenones which were stereospecifically functionalized by palladium-mediated allylation and hydroxybutenylation. Treatment with Br-2/DMSO led to stereospecific bromodemercuration. The 1-(1-alkynyl)-4-methoxy-4-methyl-2-cyclobutenols underwent efficient and very stereoselective tandem ring expansion-functionalizations in the presence of three different allylic chlorides and a catalyst system composed of 10% Hg(OCOCF3)(2) and 10% PdCl2. All products can be obtained with a stereoselectivity greater than 99:1 at the exocyclic alkene.
Abstract An efficient and general method for the synthesis of alkyl squarates is presented. This involves the reactions of squaric acid with the desired alcohol in the presence of an orthoformate. This was applicable for the synthesis of dimethyl-, diethyl-, diisopropyl, di-n-butyl and di-t-butyl squarates in yields ranging from 77–97%. It is a convenient and safe method that can be accomplished on
Triggering apoptosis in cancer cells with an analogue of cribrostatin 6 that elevates intracellular ROS
作者:D. J. Asby、M. G. Radigois、D. C. Wilson、F. Cuda、C. L. L. Chai、A. Chen、A. S. Bienemann、M. E. Light、D. C. Harrowven、A. Tavassoli
DOI:10.1039/c6ob01591c
日期:——
species (ROS) is both a consequence and driver of the upregulated metabolism and proliferation of transformed cells. The resulting increase in oxidativestress is postulated to saturate the cellular antioxidant machinery, leaving cancer cells susceptible to agents that further elevate their intracellular oxidativestress. Several small molecules, including the marine natural product cribrostatin 6, have
Structural Effects on Interconversion of Oxygen-Substituted Bisketenes and Cyclobutenediones
作者:Nanyan Fu、Annette D. Allen、Shinjiro Kobayashi、Thomas T. Tidwell、Sinisa Vukovic、Takeshi Matsuoka、Masaaki Mishima
DOI:10.1021/jo702312t
日期:2008.3.1
of oxygen to the cyclobutenediones 5f−h by the ArO substituents compared to alkoxy groups and to angle strain in the bridged product cyclobutenedione 5i. The reactivities of the ArO-substituted bisketenes 6f−h in CH3CN varied by a factor of 50 and gave an excellent correlation of the observed rate constants log k with the σp constants of the aryl substituents. Computational studies at the B3LYP/6-31G(d)
Cyclobutenediones 5与HO(二取代的一个),的MeO(b),环氧乙烷(Ç),我-Pro(d),吨-BuO(ë)的PhO(˚F),4- MeOC 6 H ^ 4 O(克),4- -O 2 NC 6 H 4 O(h)和3,4-桥接OCH 2 CH 2 O(i)取代基在激光快速光解后得到相应的双烯酮6a - i,通过在2075至2106和2116至2140 cm - 1之间的独特的双重红外吸收来检测。对于6b - e组,回到环丁二烯的开环反应性最大,在25°C下6e(RO = t -BuO)在异辛烷中的速率常数最高,为2.95×10 7 s - 1。6a(RO = OH,k = 2.57×10 6 s - 1在CH 3 CN中),而6f - i的反应性最低,速率常数最低,为3.8×10 4s - 1在CH 3 CN中放置6h(RO = 4-O 2 NC 6 H 4 O)。6f -
Organoytterbium Ate Complexes Extend the Value of Cyclobutenediones as Isoprene Equivalents
作者:Emma Packard、David D. Pascoe、Jacques Maddaluno、Théo P. Gonçalves、David C. Harrowven
DOI:10.1002/anie.201307193
日期:2013.12.2
Changing course: While organolithium and Grignard reagents favor addition to C1 of A (R=Me), the corresponding organoytterbium reagents add to C2 (R=tBu). Computational studies provide insights into the nature of organoytterbium species and their reactivity, and a total synthesis of (−)‐mansonone B illustrates the utility of the method in terpenoid synthesis. Tf=trifluoromethanesulfonyl.
改变方向:虽然有机锂和格氏试剂有利于A (R=Me)的 C1 上的加成,但相应的有机镱试剂会加成到 C2 (R= t Bu) 上。计算研究提供了对有机镱物种的性质及其反应性的见解,(−)-mansonone B 的全合成说明了该方法在萜类化合物合成中的实用性。Tf=三氟甲磺酰基。
Generation of 1,2-Bisketenes from Cyclobutene-1,2-diones by Flash Photolysis and Ring Closure Kinetics<sup>1</sup><sup>a</sup>
作者:Annette D. Allen、Jim D. Colomvakos、François Diederich、Ian Egle、Xiaokuai Hao、Ronghua Liu、Janusz Lusztyk、Jihai Ma、Michael A. McAllister、Yves Rubin、Kuangsen Sung、Thomas T. Tidwell、Brian D. Wagner
DOI:10.1021/ja9722685
日期:1997.12.17
The bisketenes 2 have been generated by flash photolysis, and the kinetics of their conversion to 1 have been studied by time-resolved infrared and ultraviolet spectroscopy. The rate constants of the ringclosure of 2 are correlated by the ketene stabilization parameters (SE) and with calculated barriers. The rate constant of ringclosure of the di-tert-butyl bisketene 2g to cyclobutenedione 1g is