Rapid racemization of an optically active cyclopropene derivative via ring opening, bond rotation, and ring closure

1972 ◽  
Vol 94 (8) ◽  
pp. 2882-2883 ◽  
Author(s):  
Eunice J. York ◽  
Wolfgang Dittmar ◽  
J. Ronald Stevenson ◽  
Robert G. Bergman
Keyword(s):  
Ring Opening ◽  
Optically Active ◽  
Ring Closure ◽  
Bond Rotation

A Stereochemical and Kinetic Study of the Conversion of Methyl Cyclopropyl Ketones to 4,5-Dihydrofurans

1973 ◽  
Vol 51 (10) ◽  
pp. 1487-1493 ◽  
Author(s):  
Donald Edward McGreer ◽  
James William McKinley
Keyword(s):  
Kinetic Study ◽  
Ring Opening ◽  
Photochemical Reactions ◽  
Order Reaction ◽  
Ring Closure ◽  
Hydrogen Shift ◽  
First Order ◽  
Bond Rotation ◽  
Cyclopropyl Ketones ◽  
Cis And Trans

The thermal and photochemical conversion of (1R*,2R*,3S*), (1S*,2R*,3S*), and (1S*,2R*,3R*)-1-acetyl-1,2-dimethyl-3-phenylcyclopropane (1, 2, and 3) to cis- and trans-2,3,4-trimethyl-5-phenyl-4,5-dihydrofurans has been studied. Concurrent with this reaction is an equilibration of 1, 2, and 3, a thermal ring opening of 1 by a 1,5-hydrogen shift, and a cyclopropane-to-propene type reaction under the photochemical conditions. The dihydrofuran from 1 and 2 by the thermal and photochemical conditions is 97% trans- and 3% cis- corresponding to predominant retention at the migrating carbon. The dihydrofuran formed from 3 by the thermal and photochemical reaction is 85% cis- and 15% trans- again corresponding to predominant retention. A kinetic study of the rearrangement of 1-acetyl-1-methyl-2-phenylcyclopropane to 1,2-dimethyl-5-phenyl-4,5-dihydrofuran provides Ea of 48.1 kcal/mol and log A of 14.9 for this first order reaction in the temperature range of 255–288 °C.It is concluded that the thermal and photochemical reactions occur by a non-concerted process through a common 1,3-diradical intermediate in which bond rotation and ring closure steps are competitive.

DFT studies on the diastereoselectivity of four-component Ugi reaction

2018 ◽  
Vol 17 (06) ◽  
pp. 1850039 ◽  
Author(s):  
Elaheh Sadat Sharifzadeh ◽  
Nader Zabarjad Shiraz
Keyword(s):  
Reaction Mechanism ◽  
Ring Opening ◽  
Transition States ◽  
Ugi Reaction ◽  
Ring Closure ◽  
Nucleophilic Attack ◽  
Dft Studies ◽  
Acid Base ◽  
Bond Rotation ◽  
Iminium Ion

In this study, mechanism and stereochemistry of four-component Ugi reaction was investigated theoretically. Structures of reagents, products, intermediates, and transition states were optimized at B3LYP/6-31[Formula: see text]G(d,p) level of theory. Mechanism and stereoselectivity of the reaction depended on several processes, including bond rotation, ring closure ring opening, acid-base, nucleophile-electrophile competitions, and rearrangements. These diverse phenomena were studied to provide a clearer picture of the mechanism of this valuable reaction, especially in terms of stereochemistry considerations. According to the results, (E)-oxazolidinols were considered as proper intermediates in Ugi reaction mechanism. In addition, the key point of diastereoselectivity of the reaction was under kinetic and thermodynamic controls of nucleophilic attack of isocyanide to less hindered re-face (E[Formula: see text] compared to 10.19[Formula: see text]kcal/mol for si-face) of chiral (E)-iminium ion.

The mechanism of an intramolecular Michael addition: a MNDO study

1985 ◽  
Vol 63 (12) ◽  
pp. 3510-3515 ◽  
Author(s):  
Graham W. L. Ellis ◽  
Donald F. Tavares ◽  
Arvi Rauk
Keyword(s):  
Carbonyl Compounds ◽  
Ring Opening ◽  
Carbonyl Oxygen ◽  
Ring Closure ◽  
Basic Medium ◽  
Transition Structure ◽  
Cyclization Reactions ◽  
Bond Rotation ◽  
Mndo Calculations ◽  
Medium Ring

The 5-endo-trig cyclization reactions of α′-hydroxy α,β-unsaturated carbonyl compounds to form the 3-furanone ring system has been investigated by means of MNDO calculations. In acid medium, the activation energy for ring formation is reduced by protonation of the carbonyl oxygen and by electron-releasing β-substituents, both of which facilitate torsion about the α,β-CC bond. Rotation about the α,β-CC bond is essentially complete when the transition structure is achieved. In reverse ring opening, heterolytic rupture of the C—O bond is aided by prior enolization since induced polarization of the enol π system acts to stabilize the developing cationic centre at the β-carbon. In basic medium, ring closure is hindered by the combined effects of the intrinsic barrier to cyclization and solvation of the intermediate alkoxide. Ring opening in basic medium is prevented by prohibitively high intrinsic barriers except when a strongly electron-releasing group such as p-O(−)-phenyl is at the β-carbon.

First Total Synthesis of a Fluorinated Calystegin

2010 ◽  
Vol 65 (4) ◽  
pp. 445-451 ◽  
Author(s):  
René Csuk ◽  
Erik Prell ◽  
Stefan Reißmann ◽  
Claudia Korb
Keyword(s):  
Total Synthesis ◽  
Ring Opening ◽  
Competitive Inhibitor ◽  
Ring Closure ◽  
Target Compound ◽  
Metathesis Reaction ◽  
Grubbs Catalyst ◽  
Ring Opening Reaction ◽  
Ultrasound Assisted ◽  
Key Steps

A straightforward chiral pool synthesis for the first fluorinated calystegin is described. Key steps of this synthesis include an ultrasound-assisted Zn-mediated tandem ring opening reaction followed by a Grubbs’ catalyst-mediated ring closure metathesis reaction. The target compound is a selective and competitive inhibitor for a β -glycosidase.

ChemInform Abstract: Synthesis of Functionalized Cyclophanes by Ring-Opening/Ring-Closure Cascade Reactions of Siloxycyclopropanes.

ChemInform ◽  
2010 ◽  
Vol 30 (21) ◽  
pp. no-no
Author(s):  
Astrid Ullmann ◽  
Margit Gruner ◽  
Hans-Ulrich Reissig
Keyword(s):  
Ring Opening ◽  
Cascade Reactions ◽  
Ring Closure

ChemInform Abstract: Ring Opening Ring Closure Reactions with 3-Substituted Chromones under Nucleophilic Conditions

ChemInform ◽  
2015 ◽  
Vol 46 (50) ◽  
pp. no-no
Author(s):  
Magdy A. Ibrahim ◽  
Nasser M. El-Gohary ◽  
Sara Said
Keyword(s):  
Ring Opening ◽  
Ring Closure

Furan Ring Opening—Isochromene Ring Closure: A New Approach to Isochromene Ring Synthesis.

ChemInform ◽  
2006 ◽  
Vol 37 (11) ◽  
Author(s):  
Alexander V. Butin ◽  
Valdimir T. Abaev ◽  
Vladimir V. Mel'chin ◽  
Artem S. Dmitriev
Keyword(s):  
Ring Opening ◽  
Furan Ring ◽  
Ring Closure ◽  
New Approach ◽  
Ring Synthesis

An unexpected thermal-ring-rearrangement of benzochromenes to inden-3-yl-naphthols with pTsOH

2018 ◽  
Vol 16 (42) ◽  
pp. 7920-7925 ◽  
Author(s):  
Srinivasarao Yaragorla ◽  
Tabassum Khan
Keyword(s):  
Ring Opening ◽  
Ring Closure ◽  
Acid Catalysts ◽  
First Report

Described here is the first report of an unexpected thermal-ring rearrangement (TRR) of benzochromenes to indene derivatives promoted by pTsOH, which proceeds through the protonation of benzochromenes by an acid catalysts followed by ring-opening and ring-closure by an intramolecular Friedel–Crafts cyclization.

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