scholarly journals Intramolecular Capture of HDDA-Derived Benzynes: (i) 6- to 12-Membered Ring Formation, (ii) Internally (vis-à-vis Remotely) Tethered Traps, and (iii) Role of the Rate of Trapping by the Benzynophile

2017 ◽  
Vol 20 (1) ◽  
pp. 88-91 ◽  
Author(s):  
Yuanxian Wang ◽  
Thomas R. Hoye
Keyword(s):  
Membered Ring ◽  
Ring Formation

Norbornene in Organic Synthesis

Synthesis ◽  
2018 ◽  
Vol 50 (15) ◽  
pp. 2799-2823 ◽  
Author(s):  
Jianhui Huang ◽  
Caifeng Li ◽  
Liu Liu ◽  
Xuegang Fu
Keyword(s):  
Ring Opening ◽  
Membered Ring ◽  
Ring Formation ◽  
Oxidation Reactions ◽  
Organic Transformations ◽  
Substitution Reactions ◽  
Reaction Conditions ◽  
Multistep Synthesis ◽  
Palladium Catalyzed

The norbornene skeleton possesses an alkene functionality with a fixed conformation, and represents unique reactivity. The use of norbornene and analogues as substrates is overviewed; reactivities are discussed as well as the role of norbornenes as ligands assisting modern organic transformations.1 Introduction2 Synthesis of Substituted Norbornenes2.1 Preparation of Functionalized Norbornenes by Deprotonation and Substitution Reactions2.2 Preparation of Functionalized Norbornenes under Palladium-Catalyzed­ Reaction Conditions2.3 Alkylation of Norbornene2.4 Multistep Synthesis3 Synthesis of Substituted Norbornanes3.1 Three-Membered-Ring Formation3.2 Formation of Four-Membered Rings3.3 Five- and Six-Membered Ring Formation3.4 Syntheses of Difunctionalized Norbornanes4 Synthesis of Cyclopentanes4.1 Oxidation Reactions4.2 Ring-Opening Cross Metathesis (ROCM)4.3 Ring-Opening Metathesis Polymerization (ROMP)4.4 Palladium-Catalyzed Ring-Opening of Norbornene5 Norbornene-Mediated Reactions5.1 Palladium Insertion into Carbon–Halide Bonds5.2 Palladium Insertion into N–H and C–H Bonds5.3 Norbornene as Ligand in Mediated Reactions6 Conclusion

On the Concerted Ring Opening of Protonated Squalene Oxide and A-Ring Formation in the Biosynthesis of Lanosterol

2003 ◽  
Vol 68 (1) ◽  
pp. 202-210 ◽  
Author(s):  
B. Andes Hess
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Reaction Pathway ◽  
Ring Expansion ◽  
Membered Ring ◽  
Ring Formation ◽  
Ring Closure ◽  
Primary Role ◽  
Transition Structure

Density functional calculations were performed on a model system of squalene oxide to study the mechanism of the formation of ring A in the biosynthesis of lanosterol from squalene. When (2Z)-6,7-epoxy-3,7-dimethyloct-2-ene was protonated, it was calculated to undergo a very facile ring opening of the oxirane in concert with the formation of the six-membered ring of the 4-(hydroxymethyl)-1,2,3,3-tetramethy1cyclohexyl cation. A study of the reaction pathway (IRC) indicates a very early transition structure in which the carbon- carbon double bond participates anchimerically in the ring-opening of the protonated oxirane. It is suggested that the primary role of the enzyme in this first step of the biosynthesis of lanosterol is protonation of the oxirane ring along with holding the substrate in the proper conformation for the concerted ring-closure to occur. The similarity between this mechanism and that recently proposed for concerted C-ring expansion and D-ring formation in the biosynthesis of lanosterol is discussed.

Ring formation via β-keto ester dianions

1977 ◽  
Vol 55 (6) ◽  
pp. 996-1000 ◽  
Author(s):  
Phaik-Eng Sum ◽  
Larry Weiler
Keyword(s):  
Membered Ring ◽  
Ring Formation ◽  
Methyl Acetoacetate ◽  
Keto Ester ◽  
Keto Esters

The reaction of α,ω-dihalides with the dianion of methyl acetoacetate gives a mixture of mono- and bisalkylated products. The monoalkylated products can be cyclized via the monoanion to cyclic β-keto esters with a seven- or eight-membered ring. Alternatively these monoalkylated products can be cyclized via the dianion to γ-cyclopentyl- or γ-cyclohexyl-β-keto esters.

scholarly journals The preparation of a 10-membered ring macrolactone by selective ozonolysis and the role of the dihydropyran-substituent on the MCPBA-oxidation reaction profile of beta-lapachone phenazines

2005 ◽  
Vol 16 (5) ◽  
pp. 1074-1077 ◽  
Author(s):  
Raphael S. F. Silva ◽  
Tiago T. Guimarães ◽  
Daniel V. Teixeira ◽  
Ana Paula G. Lobato ◽  
Maria do Carmo F. R. Pinto ◽  
...  
Keyword(s):  
Oxidation Reaction ◽  
Membered Ring ◽  
Reaction Profile

Annulation of Indoles with 1,n-Dibromoalkanes by a Pd(II)-Catalyzed and Norbornene-Mediated Reaction Cascade

Synthesis ◽  
2019 ◽  
Vol 52 (08) ◽  
pp. 1231-1238 ◽  
Author(s):  
Michael Henkel ◽  
Thorsten Bach
Keyword(s):  
Direct Synthesis ◽  
Membered Ring ◽  
Ring Formation ◽  
Cascade Process

Employing 1,3-dibromopropane, 1,4-dibromobutane, and 1,5-dibromopentane as biselectrophiles, the annulation of indoles was probed in the presence of PdCl2(MeCN)2 as a catalyst and norbornene as a transpositional ligand. Ring formation to a five-membered ring was observed at positions C2 and N, while annulation of a six-membered ring occurred at positions C2 and C3. The latter cascade process was successfully applied to the direct synthesis of 1,2,3,4-tetrahydrocarbazoles from indoles (11 examples, 31–68% yield). Seven-membered-ring annulation was feasible by an initial coupling at positon C2 followed by alkylation at C3.

Six- versus Five-Membered Ring Formation in Radical Cyclizations of 7-Bromo-Substituted Hexahydroindolinones

2004 ◽  
Vol 6 (6) ◽  
pp. 917-920 ◽  
Author(s):  
Paitoon Rashatasakhon ◽  
Ayse Daut Ozdemir ◽  
Jerremey Willis ◽  
Albert Padwa
Keyword(s):  
Membered Ring ◽  
Ring Formation ◽  
Radical Cyclizations
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