ChemInform Abstract: Ring Closure and Ring Expansion Reactions in Bridged Triarylphosphanes and Triarylarsanes with o-Isopropenyl Substituents. Novel Candidates for Turnstile Geometry.

ChemInform ◽  
1990 ◽  
Vol 21 (36) ◽  
Author(s):  
D. HELLWINKEL ◽  
A. WIEL ◽  
G. SATTLER ◽  
B. NUBER
Keyword(s):  
Ring Expansion ◽  
Ring Closure

Synthesis of 5-Aryl- 1,4-benzoxazepine and 6-phenyl-2H-1,5-benzoxazocine derivatives

1984 ◽  
Vol 37 (1) ◽  
pp. 129 ◽  
Author(s):  
JB Bremner ◽  
EJ Browne ◽  
IWK Gunawardana
Keyword(s):  
Aromatic Ring ◽  
Sodium Tetrahydroborate ◽  
Phosphorus Oxychloride ◽  
Ring Expansion ◽  
Ring Closure ◽  
Dilute Solution ◽  
Type Reaction ◽  
Chlorine Substituent

Four 5-aryl-2,3-dihydro-1,4-benzoxazepines (5a-d), with electron-releasing substituents, were prepared by a Bischler-Napieralski-type reaction of N-(2-aryloxyethyl)benzamides with phosphorus oxychloride in butanenitrile or ethanenitrile. Analogous 2,3-dihydro-1,4-benzoxazepines (12a, b), with hydrogen only or a chlorine substituent in the fused aromatic ring, were prepared by C-N ring-closure reactions. Cyclization of a dilute solution of N-[3-(3-methoxyphenoxy)propyl]benzamide (21) with phosphorus oxychloride in ethanenitrile gave a 40% yield of 9-methoxy-6-phenyl-3,4-dihydro- 2H-1,5-benzoxazocine (22). The seven- and eight-membered cyclic imines were converted into their methiodide salts (6a-d), (15a,b) and (24). These were reduced with sodium tetrahydroborate to yield the 5-aryl-4-methyl-2,3,4,5-tetrahydro-1,4-benzoxazepines (7a-d) and (l6a,b), and the 9-methoxy- 5-methyl-6-phenyl-3,4,5,6-tetrahydro-2H-1,5-benzoxazocine (25). These products were prepared for use as starting materials in ring-expansion reactions through the Meisenheimer rearrangement.

Interconversion of Nitrenes, Carbenes, and Nitrile Ylides by Ring Expansion, Ring Opening, Ring Contraction, and Ring Closure: 3-Quinolylnitrene, 2-Quinoxalylcarbene, and 3-Quinolylcarbene

2009 ◽  
Vol 62 (3) ◽  
pp. 275 ◽  
Author(s):  
David Kvaskoff ◽  
Ullrich Mitschke ◽  
Chris Addicott ◽  
Justin Finnerty ◽  
Pawel Bednarek ◽  
...  
Keyword(s):  
Ir Spectra ◽  
Ring Opening ◽  
Density Functional ◽  
Diazo Compound ◽  
Density Functional Theory Calculations ◽  
Ring Expansion ◽  
Uv Spectra ◽  
Ring Closure ◽  
High Yield ◽  
Uv And Ir Spectra

Photolysis of 3-azidoquinoline 6 in an Ar matrix generates 3-quinolylnitrene 7, which is characterized by its electron spin resonance (ESR), UV, and IR spectra in Ar matrices. Nitrene 7 undergoes ring opening to a nitrile ylide 19, also characterized by its UV and IR spectra. A subsequent 1,7-hydrogen shift in the ylide 19 affords 3-(2-isocyanophenyl)ketenimine 20. Matrix photolysis of 1,2,3-triazolo[1,5-c]quinoxaline 26 generates 4-diazomethylquinazoline 27, followed by 4-quinazolylcarbene 28, which is characterized by ESR and IR spectroscopy. Further photolysis of carbene 28 slowly generates ketenimine 20, thus suggesting that ylide 19 is formed initially. Flash vacuum thermolysis (FVT) of both 6 and 26 affords 3-cyanoindole 22 in high yield, thereby indicating that carbene 28 and nitrene 7 enter the same energy surface. Matrix photolysis of 3-quinolyldiazomethane 30 generates 3-quinolylcarbene 31, which on photolysis at >500 nm reacts with N2 to regenerate diazo compound 30. Photolysis of 30 in the presence of CO generates a ketene (34). 3-Quinolylcarbene 31 cyclizes on photolysis at >500 nm to 5-aza-2,3-benzobicyclo[4.1.0]hepta-2,4,7-triene 32. Both 31 and 32 are characterized by their IR and UV spectra. FVT of 30 yields a mixture of 2- and 3-cyanoindenes via a carbene–carbene–nitrene rearrangement 31 → 2-quinolylcarbene 39 → 1-naphthylnitrene 43. The reaction mechanisms are supported by density functional theory calculations of the energies and spectra of all relevant ground and transition state structures at the B3LYP/6–31G* level.

Advancing macromolecular hoop construction: recent developments in synthetic cyclic polymer chemistry

2021 ◽  
Vol 12 (7) ◽  
pp. 958-969
Author(s):  
Teng-Wei Wang ◽  
Matthew R. Golder
Keyword(s):  
Ring Expansion ◽  
Ring Closure ◽  
Polymer Chemistry ◽  
Linear Polymers ◽  
Synthetic Methodology ◽  
Cyclic Polymer ◽  
Recent Developments

Synthetic methodology to access cyclic macromolecules continues to develop via two distinct mechanistic classes: ring-expansion of macrocyclic initiators and ring-closure of functionalized linear polymers.

Synthesis of Tryptamines through a Novel Brønsted Acid Mediated Tandem Reaction Initiated by α-Iminol Rearrangement of Transient 2-Substituted 2-Hydroxycyclobutylimines

Synthesis ◽  
2020 ◽  
Author(s):  
Angelo Frongia ◽  
Lorenzo Serusi ◽  
Federico Cuccu ◽  
Francesco Secci ◽  
David J. Aitken
Keyword(s):  
Condensation Reaction ◽  
Ring Expansion ◽  
Ring Closure ◽  
Tandem Reaction ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brönsted Acid ◽  
Rearrangement Process

AbstractA novel Brønsted acid promoted condensation reaction between a primary aniline and 2-hydroxycyclobutanone provides access to diverse tryptamine derivatives in moderate to good yields. The proposed mechanism involves an α-iminol rearrangement, ring expansion, ring closure, and a depart-and-return rearrangement process.

Molecular Iodine-Mediated Synthesis of 2-Azaanthraquinones from [3.3.3]Propellanes via a Metal-Free Rearrangement

Synthesis ◽  
2021 ◽  
Author(s):  
Abdolali Alizadeh ◽  
Akram Bagherinejad ◽  
Mojtaba Khanpour
Keyword(s):  
Ring Opening ◽  
Bond Formation ◽  
Ring Expansion ◽  
Molecular Iodine ◽  
Ring Closure ◽  
Reaction Conditions ◽  
Metal Free ◽  
Green Conditions

AbstractA novel iodine-mediated rearrangement of heterocyclic [3.3.3]propellanes under green conditions is described. This metal-free transformation for the straightforward synthesis of substituted 2-azaanthraquinones proceeds via ring opening/dissociation of C–O and C–N bonds/intramolecular C(sp3)–C(sp3) bond formation/ring expansion/aza-ring closure/1,3-N to N alkyl migration. High atom-efficiency, synthetically useful yields, easily accessible starting materials, and mild reaction conditions are advantages of this process.

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.

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