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.

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.

A Density Functional Theory Study on the Ring-Opening Polymerization of D-Lactide Catalyzed by a Bifunctional-Thiourea Catalyst

2009 ◽  
Vol 62 (2) ◽  
pp. 157 ◽  
Author(s):  
Rong-Xiu Zhu ◽  
Ruo-Xi Wang ◽  
Dong-Ju Zhang ◽  
Cheng-Bu Liu
Keyword(s):  
Density Functional Theory ◽  
Ring Opening ◽  
Density Functional ◽  
Population Analysis ◽  
Density Functional Theory Calculations ◽  
Ring Opening Polymerization ◽  
Acyl Transfer ◽  
Frontier Molecular Orbital ◽  
Functional Theory ◽  
Elimination Pathway

The thiourea-catalyzed methanolysis of d-lactide, a model system for the initiation and propagation of the organocatalyzed ring-opening polymerization (ROP) of lactide, has been studied by performing density functional theory calculations. Both the catalyzed and uncatalyzed reactions are explored along two possible pathways: one involves the stepwise addition–elimination pathway and the other is related to the concerted pathway. It is found that the reaction without the presence of the catalyst is difficult because the barrier involved is as high as 176 kJ mol–1. With the aid of a thiourea catalyst, the barrier is reduced to 88 kJ mol–1 with a preference for the stepwise addition–elimination mechanism over the concerted one. The role of the catalyst has been rationalized by analyzing the frontier molecular orbital interactions between the catalyst and substrates and by performing natural population analysis. Finally, another mechanism involving acyl transfer is discussed for the thiourea-catalyzed ROP.

Spectral Investigations of the Effects of 60Co-Gamma Irradiation on Iodothyronine and Iodotyrosines

1987 ◽  
Vol 41 (1) ◽  
pp. 74-79
Author(s):  
A. Obaid ◽  
S. Basahl ◽  
A. Diefallah ◽  
R. Abu-Eittah
Keyword(s):  
Ir Spectra ◽  
Gamma Irradiation ◽  
Uv Spectra ◽  
Uv And Ir Spectra ◽  
60Co Gamma ◽  
Carbonyl Absorption

Solids of 3-iodo-, 3–5–di-iodotyrosine and 3,5-di-iodothyronine were irradiated by 60Co-gamma irradiation for a period of about twenty hours. The effects of irradiation were investigated through a study of the UV and IR spectra of irradiated samples. UV spectra showed the presence of a new band at 360 nm which was assigned to the formation of IO−. IR spectra showed a strong carbonyl absorption and the removal of the carboxylate band in the case of thyronine only. For comparison, the spectra of the studied compounds were investigated before irradiation.

Comparison of photoenolization and alcohol release from alkyl-substituted benzoyl benzoic esters

2011 ◽  
Vol 89 (3) ◽  
pp. 331-338 ◽  
Author(s):  
Sivaramakrishnan Muthukrishnan ◽  
Tamara C.S. Pace ◽  
Qian Li ◽  
Brian Seok ◽  
Gerdien de Jong ◽  
...  
Keyword(s):  
Transition State ◽  
Density Functional ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Alkyl Substituent ◽  
Density Functional Theory Calculations ◽  
Laser Flash ◽  
Ring Closure ◽  
Solvent Density ◽  
Transition State Barrier

Photolysis of 1B in argon-saturated solutions yields 4B and releases methanol. Laser flash photolysis of 1B shows formation of biradical 2B, which has a lifetime of ~50 ns and a λmax at 330 nm. Biradical 2B undergoes an intersystem crossing to form photoenols E-3B and Z-3B with a λmax at 390 nm. Laser flash photolysis shows that the lifetimes of E-3B and Z-3B are affected by the solvent. Density functional theory calculations demonstrate that the transition-state barrier for a 1,5-H atom shift from Z-3B to regenerate 1B is affected by the ortho-alkyl substituents, whereas the stereoelectronics of the alkyl substituent affect the transition-state barrier of E-3B as it undergoes electrocyclic ring closure to form 4B. The photoreactivity of 1B was compared with its analogous methyl and isopropyl derivatives 1A and 1C, respectively, to better estimate the effect of the alkyl substituent on reactivity.

scholarly journals Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

2019 ◽  
Vol 15 ◽  
pp. 2473-2485
Author(s):  
Eric W Webb ◽  
Jonathan P Moerdyk ◽  
Kyndra B Sluiter ◽  
Benjamin J Pollock ◽  
Amy L Speelman ◽  
...  
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Undergraduate Research ◽  
Density Functional Theory Calculations ◽  
Molecular Switches ◽  
Photochromic Behavior ◽  
Functional Theory ◽  
Long Wavelength ◽  
H Nmr ◽  
Photoinduced Charge

Our undergraduate research group has long focused on the preparation and investigation of electron-deficient analogs of the perimidinespirohexadienone (PSHD) family of photochromic molecular switches for potential application as "photochromic photooxidants" for gating sensitivity to photoinduced charge transfer. We previously reported the photochemistry of two closely related and more reducible quinazolinespirohexadienones (QSHDs), wherein the naphthalene of the PSHD is replaced with a quinoline. In the present work, we report our investigation of the electrochemistry of these asymmetric QSHDs. In addition to the short wavelength and photochromic long-wavelength isomers, we have found that a second, distinct long-wavelength isomer is produced electrochemically. This different long-wavelength isomer arises from a difference in the regiochemistry of spirocyclic ring-opening. The structures of both long-wavelength isomers were ascertained by cyclic voltammetry and 1H NMR analyses, in concert with computational modeling. These results are compared to those for the symmetric parent PSHD, which due to symmetry possesses only a single possible regioisomer upon either electrochemical or photochemical ring-opening. Density functional theory calculations of bond lengths, bond orders, and molecular orbitals allow the rationalization of this differential photochromic vs electrochromic behavior of the QSHDs.

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.

scholarly journals Density Functional Theory Studies on the Synthesis of Poly(α-Amino Acid)s Via the Amine-Mediated Ring Opening Polymerizations of N-Carboxyanhydrides and N-Thiocarboxyanhydrides

2021 ◽  
Vol 9 ◽  
Author(s):  
Tianwen Bai ◽  
Botuo Zheng ◽  
Jun Ling
Keyword(s):  
Density Functional Theory ◽  
Amino Acid ◽  
Ring Opening ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
The Past

To synthesize well-defined poly (α-amino acid)s (PAAs), ring opening polymerizations (ROP) of cyclic monomers of α-amino acid N-carboxyanhydrides (NCAs) and N-thiocarboxyanhydrides (NTAs) are most widely used. In this mini-review, we summarize the mechanism details of the monomer preparation and ROP. The present study used density functional theory calculations to reveal the mechanisms together with experimental phenomena in the past decades. Detailed discussion includes normal amine mechanism and the selectivity of the initiators bearing various nucleophilic groups.

Mechanistic insights into the ring-opening of biomass derived lactones

RSC Advances ◽  
2016 ◽  
Vol 6 (16) ◽  
pp. 12932-12942 ◽  
Author(s):  
Shelaka Gupta ◽  
Rishabh Arora ◽  
Nishant Sinha ◽  
Md. Imteyaz Alam ◽  
M. Ali Haider
Keyword(s):  
Density Functional Theory ◽  
Ring Opening ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Ring Opening Reactions ◽  
Oxocarbenium Ion ◽  
Acid Catalyzed

Density functional theory calculations suggest the formation of an oxocarbenium ion intermediate in acid catalyzed ring-opening reactions of biomass derived lactones, which may play an important role in determining it's reactivity.

Regioselectivity and Reactivity of Intramolecular [2+2] Cycloaddition Reactions of Acyl Ketenes: Experimental and Theoretical Studies

Synlett ◽  
2018 ◽  
Vol 29 (14) ◽  
pp. 1836-1841 ◽  
Author(s):  
Mahboobeh Zahedifar ◽  
Hassan Sheibani ◽  
Vahid Saheb
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Cycloaddition Reaction ◽  
Density Functional Theory Calculations ◽  
Theoretical Studies ◽  
Aryl Group ◽  
Functional Theory ◽  
Electron Withdrawing Group ◽  
Experimental And Theoretical Studies ◽  
Mechanism Of The Reaction

The regioselectivity of the intramolecular [2+2] cycloaddition reaction of acyl ketenes formed from metastable mesoionic 1,3-oxazinium-4-olates was investigated by experimental and theoretical methods. The ring opening of the mesoionic N-allyl-2-(2-arylvinyl)-1,3-oxazinium-4-olates led to the formation of unstable acyl ketenes. ­Although there are four possible paths for an intramolecular [2+2] cyclo­addition reaction involving the two double bonds (vinyl and allyl), only the intramolecular [2+2] criss-cross cycloaddition reaction through the vinyl double bond occurred to give 3-allyl-3-azabicyclo[3.1.1]heptane-2,4,6-trione derivatives. These products were not formed when a strongly electron-withdrawing group was present on the aryl group of acrylamides or benzamides. To understand the mechanism of the reaction, density functional theory calculations at the M06-2X/6-31+G(d) level were performed. These revealed that the formation of some preliminary intermediates plays a significant role in the formation of mesoionic 1,3-oxazinium-4-olates.

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