Electronic effects in asymmetric hydroboration

Garner, Charles M.; Chiang, S. S. M.; Nething, Matthew; Monestel, Robert

doi:10.1016/s0040-4039(02)02013-0

Cited by 12 publications

(4 citation statements)

References 15 publications

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“…All optimized geometries showed an unsymmetric iodiranium ion 15 irrespective of the substituent R. The distance of C 2 to I remains constant at 2.24 Å, whereas the C 1 I bond lengths are significantly longer and vary from 2.97 to 3.04 Å, depending on the substituent R. Hammett correlations have been applied frequently to not only reaction rates, but also to NMR shifts, enantioselectivities, and various thermodynamic properties 23c. d, 24 The correlation of Hammett ${\sigma {{+\hfill \atop {\rm p}\hfill}}}$ constants with the calculated NBO charges at C 1 of iodiranium ions 15 has an r 2 value of 0.86, which is much better than that obtained by using Hammett σ p constants ( r 2 =0.53),25 and confirms a positive charge stabilized in the benzylic position (see Supporting Information for data). The correlation of the enantiomeric excess of iodolactonizations of unsaturated acids of type 16 , displaying different substituted aromatic moieties (Scheme ), with the Hammett ${\sigma {{+\hfill \atop {\rm p}\hfill}}}$ values also shows a good correlation ( r 2 =0.88), as depicted in Figure 7.…”

Section: Resultsmentioning

confidence: 99%

OP15.07: Benefits of early screening in fetal anomalies diagnosis

Cernea

Tudorache

Novac

et al. 2008

Ultrasound in Obstet & Gyne

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Oral poster abstractsCochrane meta-analysis about routine third trimester ultrasound included ultrasound of the 70's and 80's and no studies were really designed to answer that question. An adequate and contemporary trial would be needed. With a prospective study to describe practices, we aimed to evaluate the feasibility of a randomized trial. Methods: All women (n = 335) with a singleton foetus managed in our tertiary center since the beginning of their pregnancy and who delivered after 28 weeks were included prospectively over a 50-day period. Data about maternal characteristics, management of pregnancy and delivery, ultrasound practices and results were recorded. One hundred women had a brief personal interview to define their expectation and experience about third trimester ultrasound. Results: Women had 2.9 + / − 1.2 ultrasound scan during their pregnancy. All had a second trimester ultrasound and 53.7% had a third trimester ultrasound, without medical indication in 12.8%. Among ''low-risk'' pregnancy, 40% had a third trimester ultrasound. Of those, 21.6% were done for no medical indication. Among women interviewed who had a third trimester ultrasound scan, only 13.7% declared that this exam was stressful. Three quarter of the population interviewed would agree to join in a future trial. Conclusions: In our hospital, more than half of pregnant women had a third trimester ultrasound and this was not perceived as stressful. The recruitment for a randomized trial to evaluate the impact of routine third trimester scan on perinatal morbi-mortality in a lowrisk population will necessitate a multi-center collaboration as the sample size required is large. Until such trial is published, knowing that pregnant women will receive more than one ultrasound, health care resources should be planned for accordingly. OP15.06Does second trimester ultrasound affect normal fetal physiology?

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Section: Resultsmentioning

confidence: 99%

OP15.07: Benefits of early screening in fetal anomalies diagnosis

Cernea

Tudorache

Novac

et al. 2008

Ultrasound in Obstet & Gyne

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“…Wiskur 等 [15] 在研究手性四咪唑催化的硅化动力图 3 Pauson-Khand 反应中的底物取代基电子效应 [13] 图 4 烯丙基化反应中的非共轭取代基电子效应 [14] 学拆分的机理时, 同样发现了三芳基硅试剂的取代此外, 杨丹等 [16] 、Chan 等 [17~19] 、Garner 等 [20] 、 Mezzetti 等 [21] 、Brown 等 [22] 、Coates 等 [23] 在各自的反应体系研究中均使用过取代基常数与对映选择性的相关来研究反应机理, 在此不再一一列举.…”

Section: Hammett 参数unclassified

Linear free-energy relationships in asymmetric catalysis

Zhang¹,

Li²,

Luo³

et al. 2016

Sci. Sin.-Chim

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Chiral aldehyde catalysis: a highly promising concept in asymmetric catalysis SCIENCE CHINA Chemistry 62, 3 (2019); Quantum chemical study on asymmetric catalysis reduction of imine Science in China Series B-Chemistry 46, 124 (2003); Chiral covalent organic frameworks for asymmetric catalysis and chiral separation SCIENCE CHINA Chemistry 60, 1015 (2017); Chiral model complexes for methane monooxygenase and their asymmetric catalysis of styrene epoxidation

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“…The factors governing enantioselectivity in the catalytic asymmetric reaction are usually interpreted in steric terms, affected by the temperature and solvent, etc. 6a,7c,8c, Electronic effects have been reported to control the enantioselectivity recently. In reported studies on the electronic effects on the enantioselectivity, , the underlying reasons are poorly understood in most of the cases. It should be very useful to understand all factors that affect the enantioselectivity in this asymmetric reduction in detail.…”

Section: Introductionmentioning

confidence: 99%

Influences of Electronic Effects and Anions on the Enantioselectivity in the Oxazaborolidine-Catalyzed Asymmetric Borane Reduction of Ketones

Wei

Zhang

2004

J. Org. Chem.

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The influence of electronic effects on the enantioselectivity of the oxazaborolidine-catalyzed asymmetric borane reduction of ketones has been observed and investigated with use of para-substituted acetophenones and propiophenones with a variety of functional groups and B-unsubstituted and B-methoxyoxazaborolidines derived from (S)-2-(diphenylhydroxymethyl)pyrrolidine with borane and trimethyl borate as catalysts in toluene and THF. The results indicate that Hammett linear free energy electronic effects on the enantioselectivity in the asymmetric reduction were observed and rationalized. Tuning electronic effects of the catalyst can improve the enantioselectivity in the reduction. Another interesting finding to be noted is that anions heavily affect the enantioselectivity, especially for the B-methoxy catalyst, because of their coordination with the boron atom in the catalysts.

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Electronic effects in asymmetric hydroboration

Cited by 12 publications

References 15 publications

OP15.07: Benefits of early screening in fetal anomalies diagnosis

OP15.07: Benefits of early screening in fetal anomalies diagnosis

Linear free-energy relationships in asymmetric catalysis

Influences of Electronic Effects and Anions on the Enantioselectivity in the Oxazaborolidine-Catalyzed Asymmetric Borane Reduction of Ketones

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