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121.
Total Synthesis of C30 Botryococcene and epi‐Botryococcene by a Diastereoselective Ring Opening of Alkenylcyclopropanes
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Morgan Cormier Aurélien de la Torre Ilan Marek 《Angewandte Chemie (International ed. in English)》2018,57(40):13237-13241
Trialkylaluminum compounds perform a diastereoselective 1,6‐ring fragmentation of alkenylcyclopropane. This new tool allows the preparation of hydrocarbon compounds containing two distant stereocenters with a good diastereocontrol. Inspired by the biosynthesis of botryococcene this methodology was applied successfully to the diastereo‐ and enantioselective preparation of this triterpene and its epimer. 相似文献
122.
123.
A high yielding, one-pot general procedure for the synthesis of ò-iodoalkyne is described. 相似文献
124.
125.
The strained double bond of cyclopropenylcarbinols undergoes a facile oxidation reaction to lead to unsaturated carbonyl derivatives. The distribution of the formed products depends on the relative stability of carbon-centered radical species, and the Sharpless kinetic resolution leads to enantiomerically pure Baylis-Hillman enal adducts. 相似文献
126.
Itai Massad Dr. Heiko Sommer Prof. Dr. Ilan Marek 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15679-15683
An in situ generated cationic Ir-catalyst isomerizes simple allylic silyl ethers into valuable, fully substituted aldehyde-derived silyl enol ethers. Importantly, by judicious choice of substrate, either of the two possible stereoisomers of a given enolate derivative is accessible with complete stereoselectivity. One-pot isomerization-aldol and isomerization-allylation processes illustrate the synthetic utility of this method. 相似文献
127.
We construct a property on 0/1‐strings that has a representation by a collection of width‐3 read‐twice oblivious branching programs, but for which any two‐sided ?‐testing algorithm must query at least Ω(nδ) many queries for some fixed ? and δ. This shows that Newman's result [Testing of functions that have small width branching programs, SIAM J Comput 31 (2002), 1557–1570] cannot be generalized to read‐k‐times functions for k > 1. In addition, we exhibit a property that has also a representation by a CNF formula of constant clause size. Hence, the nontestability results extend to properties that in addition have small (constant size) 0‐witnesses. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献
128.
Oksana Stalnov Vitali Palei Ilan Fono Kelly Cohen Avi Seifert 《Experiments in fluids》2007,42(4):531-542
The effectiveness of a small array of body-mounted sensors, for estimation and eventually feedback flow control of a D-shaped
cylinder wake is investigated experimentally. The research is aimed at suppressing unsteady loads resulting from the von-Kármán
vortex shedding in the wake of bluff-bodies at a Reynolds number range of 100–1,000. A low-dimensional proper orthogonal decomposition
(POD) procedure was applied to the stream-wise and cross-stream velocities in the near wake flow field, with steady-state
vortex shedding, obtained using particle image velocimetry (PIV). Data were collected in the unforced condition, which served
as a baseline, as well as during influence of forcing within the “lock-in” region. The design of sensor number and placement
was based on data from a laminar direct numerical simulation of the Navier-Stokes equations. A linear stochastic estimator
(LSE) was employed to map the surface-mounted hot-film sensor signals to the temporal coefficients of the reduced order model
of the wake flow field in order to provide accurate yet compact estimates of the low-dimensional states. For a three-sensor
configuration, results show that the estimation error of the first two cross-stream modes is within 20–40% of the PIV-generated
POD time coefficients. Based on previous investigations, this level of error is acceptable for a moderately robust controller
required for feedback flow control. 相似文献
129.
Cover Picture: Modulable and Highly Diastereoselective Carbometalations of Cyclopropenes (Chem. Eur. J. 4/2014)
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130.
Isoxazole‐Embedded Allylic Zinc Reagent for the Diastereoselective Preparation of Highly Functionalized Aldol‐Type Derivatives Bearing a Stereocontrolled Quaternary Center
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Lydia Klier Coura R. Diène Manuel Schickinger Albrecht Metzger Andreas J. Wagner Prof. Dr. Konstantin Karaghiosoff Prof. Dr. Ilan Marek Prof. Dr. Paul Knochel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(43):14096-14101
Highly functionalized aldol‐type products bearing a β‐quaternary center and a stereoselectively controlled γ‐hydroxy function are readily prepared by the diastereoselective addition of an allylic zinc reagent embedded in an isoxazole ring to various aromatic and heteroaromatic aldehydes, in the presence of Lewis acids, such as MgCl2 or LaCl3?2 LiCl. After reductive cleavage of the N?O bond by using Fe, NH4Cl, aldol‐type products bearing a stereocontrolled β‐quaternary center and a γ‐hydroxy group were observed. The benzylic reactivity of the isoxazolylmethylzinc reagent towards other electrophiles, such as acid chlorides, aryl and allylic halides, as well as aldehydes in the presence of BF3?OEt2 are also described. 相似文献