Electrocyclic Ring-opening Reaction Research Articles

Vinylphosphonium salt mediated stereoselective synthesis of cyclobutene derivatives. A facile route to highly electron-deficient 1,3-dienes

Ethyl 4-aryl-2,4-dioxobutanoates undergo stereoselective intramolecular Wittig reaction with a vinyltriphenylphosphonium salt to yield cyclobutene derivatives, which undergo electrocyclic ring-opening reactions in boiling toluene to produce highly electron-deficient 1,3-dienes.

Synthesis of 15-Deoxy-12-hydroxy-10-(trifluoromethyl)-Delta(7)-PGA(1) Methyl Ester.

Cross-conjugated alkylidene prostaglandins have been shown to be potent cytostatic agents that exert their action through a unique and unusual mechanism. Compounds in this class also inhibit viral replication and have a role in osteogenesis and adipogenesis; consequently, they are of considerable current interest as pharmaceutical lead compounds. The purpose of our research was to define an efficent protocol for the assembly of the C-10 trifluoromethyl prostanoid mentioned in the title. This compound was predicted to show strong antitumor activity on the basis of the known structure-activity relationships within this series. A novel strategy for assembling the carbon skeleton of Delta(7)-unsaturated prostanoids bearing oxygen functionality at C-12 through an ionic electrocyclic process has been described. Key steps of the synthesis are the preparation of dieneone 14b through an electrocyclic ring-opening reaction and the ionic electrocyclization of 26a, which creates the functionalized carbon skeleton. The target compound was found to be cytotoxic in vitro against two human tumor cell lines in the low &mgr;M range, confirming our prediction.

On the Reactivity of Diazadiphosphetidine Derivatives Towards Electrophilic Agents, a Mndo Study

Abstract The utilization of σ3λ3 diazadiphosphetidine as precursor of the potentially useful1 cyclodiphosphazenes has shown some interestings facts on the reactivity of the intermediates The monoinsaturated diazadiphosphetines are relatively unstable and undergo an electrocyclic ring opening reaction, even at low temperature. the PI11 atom in the monocationic and monoinsaturated derivatives show a lack of the phosphine character.

Density functional studies of representative pericyclic reactions

Density functional theory (DFT) has traditionally been shunned by computational chemists, but has long seen widespread use in the physics community. Recently, however, DFT has been adopted by the ab initio quantum chemistry community and much activity has been devoted to refining the methodology and exploring the range of its applicability. We investigate the use of DFT (both local (LDF) and non-local (NLDF) spin density approximations) to calculate transition and equilibrium structures for three representative pericyclic reactions: the electrocyclic ring opening reaction of cyclobutene, the [1,5] sigmatropic hydrogen shift reaction in (Z)-1,3-pentadiene, and the Diels-Alder cycloaddition reaction between ethylene and butadiene. LDF theory tends to overemphasize the stability of the ringed structures in each of these reactions. For example, LDF predicts a very low (6 kcal mol −1) barrier to reaction for the Deils-Alder reaction. NLDF theory substantially improves the calculated reaction barrier (20 kcal mol −1), but it is still low with respect to experiment.

Density functional studies of representative pericyclic reactions

Density functional theory (DFT) has traditionally been shunned by computational chemists, but has long seen widespread use in the physics community. Recently, however, DFT has been adopted by the ab initio quantum chemistry community and much activity has been devoted to refining the methodology and exploring the range of its applicability. We investigate the use of DFT (both local (LDF) and non-local (NLDF) spin density approximations) to calculate transition and equilibrium structures for three representative pericyclic reactions: the electrocyclic ring opening reaction of cyclobutene, the [1,5] sigmatropic hydrogen shift reaction in (Z)-1,3-pentadiene, and the Diels—Alder cycloaddition reaction between ethylene and butadiene. LDF theory tends to overemphasize the stability of the ringed structures in each of these reactions. For example, LDF predicts a very low (6kcalmol −1) barrier to reaction for the Deils—Alder reaction. NLDF theory substantially improves the calculated reaction barrier (20kcalmor −1), but it is still low with respect to experiment.

Mechanistic study of the electrocyclic ring-opening reaction of thiirane

The electrocyclic ring opening of the C−C bond in thiirane is investigated in detail within the context of ab initio molecular orbital theory. The conrotatory and disrotatory reaction pathways are studied with three different basis sets ranging from double-ξ plus polarization (DZP) through triple-ξ plus double polarization (TZ2P) in conjunction with self-consistent-field (SCF), two-configuration SCF (TCSCF), and configuration interaction with single and double excitations (CISD) levels of theory

Elektrocyclische Ringöffnung von [Cp(CO) 2Mn] 2Mn] 2SePh +

[Cp(CO) 2Mn] 2SePh + can undergo valence isomerisation, which may be rationalized in terms of an electrocyclic ring opening reaction L n MSe(R)M L n + ⇌ ▪. The valence tautomeric equilibrium was quantitatively substantiated by UV-VIS and NMR spectroscopy.

Thermal intramolecular reactions of Δ1-1,2,4-triazolines with extended exocyclic unsaturation

Fumaratotriazoline (1) and amidotriazoline (3) undergo thermal first-order transformations in solution at 65 °C. The former affords the isomeric pyrrole 5 and its hydrolysis product 6. A mechanism involving opening of the initial five-membered ring to form 8, followed by closure to a new five-membered ring (9), is proposed. Amidotriazoline (3) loses N2 on heating to form 19. The experimental results are best accommodated in terms of a novel mechanism involving an electrocyclic ring closure, a [3 + 2] cycloreversion to form an ylide, a sigmatropic rearrangement of the ylide, and, finally, an electrocyclic ring-opening reaction.

Intramolecular reaction between nitro and carbodi-imide groups; a new synthesis of 2-arylbenzotriazoles

1-(2-Nitrophenyl)-5-phenyltetrazole (5b) decomposes when heated to give nitrogen, carbon dioxide, and 2-phenylbenzotriazole (6) in high yield. This new molecular rearrangement proceeds via 2-nitrophenyl(phenyl)carbodi-imide (8). Other precursors of this carbodi-imide, i.e. oxadiazolone (10), oxadiazolethione (11), oxathiadiazole 2-oxide (12), and the aminimide (16), and carbodi-imide itself, all give 2-phenylbenzotriazole (6) on thermolysis, the last three in high yield. This reaction is general for diarylcarbodi-imides with an ortho nitro group, and their precursors, and it provides a useful new route to 2-arylbenzotriazoles. A sequence of electrocyclic ring closing and opening reactions (Scheme 5) is proposed as the mechanism of this process. The key intermediate, 2-phenyl-1,2,4-benzotriazin-3-one 1-oxide (19), has been isolated from a careful thermolysis of (12) in toluene; in solution it is in reversible equilibrium with the ring-opened form (20). This new nitro-carbodi-imide group interaction has been extended to the more stable nitrobiphenyl(phenyl)carbodi-imide (25) and nitronaphthyl(phenyl)-carbodi-imide (24) which, on flash vacuum pyrolysis, give benzimidazo[1,2-f]phenanthridine (29) and benz[cd]indazole 1-oxide (32) respectively, in new rearrangements.

Emission spectra of photochromic spiro[1,8- a]dihydroindolizines and mechanism of the electrocyclic ring opening reaction

The photochemical pericyclic ring opening of the new photochromic system of spiro[1,8- a]dihydroindolizines (DHIs) was studied. From absorption and emission spectra the singlet energy E(S 1) of the DHIs was calculated to be of the order of 60 – 70 kcal mol −1. Measurements of the fluorescence quantum yields φ F and the singlet lifetimes τ s of the DHIs (at room temperature and 77 K) as well as quenching experiments gave radiative lifetimes τ rs which are two orders of magnitude larger than the τ rs values calculated by the Strickler—Berg equation, suggesting that the two excited singlets involved in absorption and emission are not the same. From negative reaction quenching and negative chemiexcitation by dioxetane the excited state of the DHIs was concluded to be a singlet. The pericyclic ring opening may therefore be regarded as a fast singlet reaction.

Electrocyclic ring opening reaction of a 1,3,4-oxadiazin-6-one into its azaketene tautomer

5-Methyl-2-phenyl-1,3,4-oxadiazin-6-one undergoes cycloaddition with 2-methylpropenylpyrrolidine. One of the cycloadducts is derived from the Diels-Alder reaction of a transient azaketene tautomer.

NMR study of the intramolecular nonmutual exchange of 5-halobenzofuroxan. II. Mechanism of ring opening reaction.

The tautomerism of 5-chlorobenzofuroxan, 5-bromobenzofuroxan, and 5-iodobenzofuroxan was studied by the proton magnetic resonance (PMR) at 60 MHz. The rate of intramolecular rearrangement between the tautomers was calculated from the PMR line shape, using the density matrix method of intramolecular nonmutual exchange. The activation parameters for the intramolecular rearrangement were found to be ⊿H≐̸=5∼24 kcal/mol, ⊿S≐̸=-34∼+33 cal/deg·mol. Structure of the transition state is discussed from electronic energies of the system and it was concluded that this reaction proceeds via a transition state of ψ-o-dinitrosobenzene produced by the electrocyclic ring opening reaction of benzofuroxan.

Electrocyclic Ring Opening Reactions of Ethylene Oxides

AbstractSubstituents capable of stabilizing negative charge endow ethylene oxides with the ability to undergo electrocyclic ring opening at the CC bond; heating or irradiation generates small equilibrium concentrations of carbonyl ylides which can engage in 1,3‐dipolar cycloadditions. Apart from the normal conrotatory mode of ring opening, predicted by the Woodward‐Hoffmann rules, the disrotatory process, forbidden by orbital symmetry, also appears to occur in the case of α‐cyano‐cis‐stilbene oxide. Kinetic studies on α‐cyano‐trans ‐and ‐cis‐stilbene oxide permit construction of the energy profile for electrocyclic ring opening to give the stereoisomeric carbonyl ylides and for their recyclization and rotation.

ChemInform Abstract: GRIGNARD‐ADDITION AN PYRIDIN‐N‐OXID

AbstractPyridin‐N‐oxid (I) addiert die Grignardverbindungen (II) zu den Aldoximen (IV) mit ′ (E), (Z), (E)‐Konfiguration, die durch eine elektrocyclische Ringöffnung‐Reaktion der prim. gebildeten Grignardaddukte (III) entstehen.

Grignard‐Addition an Pyridin‐N‐oxid

AbstractAddition of phenyl‐, alkyl‐, alkenyl‐ and alkinyl‐Grignard reagents to pyridine‐N‐oxide in THF leads to 5‐substituted (2Z, 4E)‐pentadien‐aldoximes 6 having (E) (syn)‐configuration of the C, N‐double bond. The unsaturated oximes are shown to arise through an electrocyclic ring opening reaction from the primary Grignard adducts 5. These can be trapped by protonation at low temperature.