Step-wise induction, amplification and inversion of molecular chirality through the coordination of chiral diamines with Zn(ii) bisporphyrin

2015 ◽  
Vol 51 (5) ◽  
pp. 895-898 ◽  
Author(s):  
Sk Asif Ikbal ◽  
Sanfaori Brahma ◽  
Sankar Prasad Rath
Keyword(s):  
Supramolecular Complex ◽  
Optically Active ◽  
Chirality Transfer ◽  
Molecular Chirality ◽  
Chiral Diamines ◽  
And Inversion ◽  
First Time ◽  
Origin Of Chirality

A clear structural rationalization of the origin of chirality transfer from an optically active diamine guest to an achiral Zn(ii) bisporphyrin host in a 1 : 1 and 2 : 3 host–guest supramolecular complex has been demonstrated for the first time. During the process, chirality inversion along with amplification was observed.

Central–axial–central chirality transfer: asymmetric synthesis of highly substituted indenes bearing a stereogenic quaternary carbon center from optically active propargyl alcohols

2015 ◽  
Vol 51 (2) ◽  
pp. 380-383 ◽  
Author(s):  
Masahiro Egi ◽  
Kaori Shimizu ◽  
Marin Kamiya ◽  
Yuya Ota ◽  
Shuji Akai
Keyword(s):  
Asymmetric Synthesis ◽  
Optically Active ◽  
Quaternary Carbon ◽  
Chirality Transfer ◽  
Propargyl Alcohols

An asymmetric synthesis of highly substituted indenes has been developed via the central–axial–central chirality transfer from optically active propargyl alcohols.

Bifunctional squaramide catalyzed stereoselective Mannich reaction of α-azido ketones with isatin-derived ketimines

2020 ◽  
Vol 18 (3) ◽  
pp. 479-487 ◽  
Author(s):  
Seda Karahan ◽  
Cihangir Tanyeli
Keyword(s):  
Mannich Reaction ◽  
Optically Active ◽  
First Time ◽  
High Stereoselectivity

Bifunctional squaramide catalyzed asymmetric Mannich reaction of alpha-azido ketones and isatin derived ketiminines were established for the first time with high stereoselectivity. Adducts are valuable synthons for optically active heterocycles.

Temperature and composition measurements from the l.r.i.r. and l.i.m.s. experiments on Nimbus 6 and 7

1980 ◽  
Vol 296 (1418) ◽  
pp. 205-218 ◽  
Keyword(s):  
High Precision ◽  
Trace Gas ◽  
Transport Problems ◽  
Rocket Measurements ◽  
Inversion Techniques ◽  
And Inversion ◽  
First Time ◽  
Good Agreement ◽  
Composition Measurements

The limb radiance inversion radiometer (l.r.i.r.) on Nimbus 6 was the first orbiting infrared limb scanner. It had four channels with which to determine temperature, Oz and H aO in the stratosphere and low mesosphere. The limb infrared monitor of the stratosphere (l.i.m.s.) is a similar six-channel instrument launched on Nimbus 7 in October 1978 to measure temperature, O 3 , H 2 O , NO 2 and HNO 3 . The instrumentation and inversion techniques are briefly described. In this method, the outwelling radiance in the 15 pm bands of CO 2 is inverted to yield temperatures as a function of pressure; the temperature is then used w ith the radiance emitted by a trace gas to determine its concentration. L.r.i.r. temperature and ozone results show high precision and good agreement with rocket measurements from the tropopause into the mesosphere. Preliminary l.i.m.s. results show that temperatures may be retrieved into the troposphere, and the capability to determine constituent concentrations in the part / 10 9 range from a satellite for the first time. The application of such data for photochemical dynamical and transport problems is discussed.

Thermal rearrangement of optically active tetradeuterated 2-methoxymethyl-methylenecyclopropane and the bent bond/antiperiplanar hypothesis

2019 ◽  
Vol 17 (29) ◽  
pp. 7007-7012 ◽  
Author(s):  
Ghislain Deslongchamps ◽  
Pierre Deslongchamps
Keyword(s):  
Mechanistic Model ◽  
Optically Active ◽  
Thermal Rearrangement ◽  
First Time

The bent bond/antiperiplanar hypothesis (BBAH) provides, for the first time, a mechanistic model that rationalizes methylenecyclopropane rearrangements.

An unprecedented porphyrin-pillar[5]arene hybrid ditopic receptor

RSC Advances ◽  
2015 ◽  
Vol 5 (54) ◽  
pp. 43218-43224 ◽  
Author(s):  
Nana Sun ◽  
Xin Xiao ◽  
Chenxi Liu ◽  
Chao Chen ◽  
Jianzhuang Jiang
Keyword(s):  
Supramolecular Complex ◽  
Active Centers ◽  
Host Compound ◽  
Ditopic Receptor ◽  
First Time

A porphyrin-pillar[5]arene hybrid host compound with a ditopic receptor nature was synthesized for the first time, which combines a neutral 1,4-bis(imidazol-1-yl)butane guest by means of its two active centers to form a stable supramolecular complex.

Temperature-Controlled Bidirectional Enantioselectivity in Asymmetric Hydrogenation Reactions Utilizing Stereodynamic Iridium Complexes

Synthesis ◽  
2017 ◽  
Vol 49 (15) ◽  
pp. 3485-3494 ◽  
Author(s):  
Max Siebert ◽  
Golo Storch ◽  
Frank Rominger ◽  
Oliver Trapp
Keyword(s):  
Elevated Temperatures ◽  
Asymmetric Hydrogenation ◽  
Iridium Complexes ◽  
Chirality Transfer ◽  
Iridium Catalysts ◽  
Thermal Equilibration ◽  
Hydrogenation Reactions ◽  
Temperature Controlled ◽  
First Time ◽  
Solid State Structures

Stereochemically flexible 2,2(-bis(diphenylphosphino)biphenyl (BIPHEP) ligands were modified with chiral α-substituted carboxylic acid auxiliaries in the 3- and 3′-position. The resulting central-to-axial chirality transfer to the stereochemically flexible chiral axis of the BIPHEP­ core was investigated as well as complexation of these diastereomeric ligands to iridium(I). Solid-state structures of both ligand diastereomers and a diastereomerically pure iridium(I) BIPHEP complex were obtained. Thermal equilibration of the resulting iridium(I) complexes was studied to investigate the stereodynamic properties of the BIPHEP ligands. The iridium(I) complexes without and after pre-catalysis warming in solution — which induces a shift of the diastereomeric ratio — were applied for asymmetric hydrogenation of a prochiral α-substituted acrylic acid, resulting in temperature-controlled bidirectional enantioselectivity of iridium catalysts for the first time. In both cases, enantioenriched (R)-naproxen as well as (S)-naproxen — after re-equilibration of the catalyst at elevated temperatures — was obtained by using the same catalyst.

Chirality Transfer during the [2,3]-sila-Wittig Rearrangement and Cyclopropanation Reaction of Optically Active [(sec-Allyloxy)silyl]lithiums

2001 ◽  
Vol 123 (13) ◽  
pp. 3143-3144 ◽  
Author(s):  
Atsushi Kawachi ◽  
Hirofumi Maeda ◽  
Hiroshi Nakamura ◽  
Noriyuki Doi ◽  
Kohei Tamao
Keyword(s):  
Optically Active ◽  
Chirality Transfer ◽  
Wittig Rearrangement
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