Sequential radical ring closure-radical ring opening: use in the preparation of benzofurans

1991 ◽  
Vol 56 (18) ◽  
pp. 5285-5289 ◽  
Author(s):  
Derrick L. J. Clive ◽  
Sylvain Daigneault
Keyword(s):  
Ring Opening ◽  
Ring Closure ◽  
Radical Ring

Cyclization of 5-hexenyl radicals from nitroxyl radical additions to 4-pentenylketenes and from the acyloin reaction

2003 ◽  
Vol 81 (6) ◽  
pp. 697-704 ◽  
Author(s):  
Huda Henry-Riyad ◽  
Thomas T Tidwell
Keyword(s):  
Ring Opening ◽  
Hydrogen Transfer ◽  
Nitroxyl Radical ◽  
Reaction Times ◽  
Major Product ◽  
Radical Cyclization ◽  
Ring Closure ◽  
Radical Ring ◽  
Intermediate Radical ◽  
Hydrocarbon Solvents

Photochemical Wolff rearrangements were used to form 5-substituted-4-pentenylketenes 1a–1d (RCH=CHCH2XCH2CH=C=O: 1a R = H, X = CH2; 1b R = Ph, X = CH2; 1c R = c-Pr, X = CH2; 1d R = H, X = O), which were observed by IR at 2121, 2120, 2119, and 2126 cm–1, respectively, as relatively long-lived species at room temperature in hydrocarbon solvents. These reacted with the nitroxyl radical tetramethylpiperidinyloxyl (TEMPO, TO·) forming carboxy-substituted 5-hexenyl radicals 3, which were trapped by a second nitroxyl radical forming 1,2 diaddition products 4a–4d. On thermolysis, 4a–4d underwent reversible reformation of the radicals 3, which underwent cyclization forming cyclopentanecarboxylic acid derivatives 6 or 11 as the major products. However, in the case of 1b, the cyclopentane derivative was formed reversibly and on prolonged reaction times the only product isolated was PhCH=CH-(CH2)4CO2H (8b) from hydrogen transfer to Cβ and cleavage of the TEMPO group. Cyclopropylcarbinyl radical ring opening in the cyclized radical 5c from 1c led to the 2-(4-N-tetramethylpiperidinyloxybut-1-enyl)cyclopentane derivative 11 as the major product. In a test for 5-hexenyl radical ring closure in the radical anion intermediate of the acyloin condensation, the ester CH2=CH(CH2)3CO2Et (12a) gave the acyloin 13a (76%) as the only observed product, while PhCH=CH(CH2)3CO2CH3 (12b) with Na in toluene gave 21% of the acyloin product 13b and 42% of 2-benzylcyclopentanol (15) from cyclization of the intermediate radical anion.Key words: ketenes, free radical cyclization, TEMPO, acyloin condensation.

TiCp2Cl-Catalyzed Living Radical and Ring Opening Polymerizations Initiated from Epoxides and Aldehydes in the Synthesis of Linear, Graft and Branched Polymers

2004 ◽  
Vol 856 ◽  
Author(s):  
Alexandru D. Asandei ◽  
Isaac W. Moran ◽  
Gobinda Saha ◽  
Yanhui Chen
Keyword(s):  
Electron Transfer ◽  
Ring Opening ◽  
Glycidyl Methacrylate ◽  
Ring Opening Polymerization ◽  
Branched Polymers ◽  
Single Electron Transfer ◽  
Radical Ring ◽  
Polymer Architectures ◽  
Complex Polymer

ABSTRACTTi(III)Cp2Cl-catalyzed radical ring opening (RRO) of epoxides or single electron transfer (SET) reduction of aldehydes generates Ti alkoxides and carbon centered radicals which add to styrene, initiating a radical polymerization. This polymerization is mediate in a living fashion by the reversible termination of growing chains with the TiCp2Cl metalloradical. In addition, polymers or monomers containing pendant epoxide groups (glycidyl methacrylate) can be used as substrates for radical grafting or branching reactions by self condensing vinyl polymerization. In addition, Ti alkoxides generated in situ by both epoxide RRO and aldehyde SET initiate the living ring opening polymerization of ε-caprolactone. Thus, new initiators and catalysts are introduced for the synthesis of complex polymer architectures.

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

Radical Ring-Opening Copolymerization of 2-Methylene 1,3-Dioxepane and Methyl Methacrylate:  Experiments Originally Designed To Probe the Origin of the Penultimate Unit Effect

1999 ◽  
Vol 32 (5) ◽  
pp. 1332-1340 ◽  
Author(s):  
G. Evan Roberts ◽  
Michelle L. Coote ◽  
Johan P. A. Heuts ◽  
Leesa M. Morris ◽  
Thomas P. Davis
Keyword(s):  
Methyl Methacrylate ◽  
Ring Opening ◽  
Radical Ring

Scope and limitations of the nitroxide-mediated radical ring-opening polymerization of cyclic ketene acetals

2013 ◽  
Vol 4 (17) ◽  
pp. 4776 ◽  
Author(s):  
Antoine Tardy ◽  
Vianney Delplace ◽  
Didier Siri ◽  
Catherine Lefay ◽  
Simon Harrisson ◽  
...  
Keyword(s):  
Ring Opening ◽  
Ring Opening Polymerization ◽  
Radical Ring ◽  
Cyclic Ketene Acetals ◽  
Ketene Acetals
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