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Medium-sized rings, electrocyclic reaction, arylation, cyclobutenes, chirality transfer, Heck-Matsuda reaction Keywords: medium-sized rings; electrocyclic reaction; Heck-Matsuda reaction; arylation; cyclobutenes; chirality transfer EN medium-sized rings electrocyclic reaction Heck-Matsuda reaction arylation cyclobutenes chirality transfer 1275 1279 5 06/19/23 20230704 NES 230704 Cyclic , -unsaturated ketones are important frameworks found in many biologically active compounds, naturally occurring substances, and versatile intermediates used to synthesize these molecules. [20] The reaction proceeds via the I cis i , I trans i -cycloocta-1,3-dienes B 2 b , formed as short-lived and highly reactive intermediates by a reversible conrotatory 4 -electrocyclic ring-opening reaction followed by a Pd-catalyzed Mizoroki-Heck reaction at the more-distorted I trans i -double bond. The chirality of (-)- B 5aa b should be induced by the stereoselective insertion of an aryl palladium species into the distorted I trans i -double bond of optically active B 2 b . [Extracted from the article]

A convenient procedure to access 1-[(1,1′-biphenyl)-4-yl]naphthalene by the Stevens rearrangement of the aminium salts bearing simultaneously 3-phenylprop-2-enyl and [3-(α-naphthyl)prop-2-ynyl] moieties was developed. During vacuum distillation, the synthesized compounds underwent the domino reaction to afford 1-[(1,1′-biphenyl)-4-yl]naphthalene. On the first step of this reaction, β-elimination of secondary amines gave the conjugated dienyne; on the second step, the electrocyclic reaction of dienyne resulted in cyclic allene intermediate; on the third step, allene intermediate rapidly transformed to 1-[(1,1′-biphenyl)-4-yl]naphthalene via either 1,3- or 1,5-hydrogen shift. [ABSTRACT FROM AUTHOR]

Strigolactones are apocarotenoids known as phytohormones and rhizosphere semiochemicals. Orobanchol, originally isolated from red clover, is recognized as one of the representative canonical strigolactones. A considerable number of naturally occurring orobanchol derivatives have been identified so far, and alectrol (orobanchyl acetate), fabacyl acetate, 7-oxoorobanchol, and 7-hydroxyorobanchol are known as orobanchol derivatives that retain its entire carbon skeleton. By combining our original synthetic method for (±)-orobanchol with enzymatic kinetic resolution, we successfully achieved the synthesis of the natural enantiomer of orobanchol and its conversion to naturally occurring orobanchol derivatives such as alectrol and fabacyl acetate. [Display omitted] • The natural enantiomer of orobanchol, a representative canonical strigolactone, was synthesized. • Alectrol and fabacyl acetate, naturally occurring orobanchol derivatives, were also synthesized. • Enzymatic kinetic resolution was employed as the key methodology. • Acid-mediated cascade cyclization was crucial for the preparation of the tricyclic lactone substrate. [ABSTRACT FROM AUTHOR]

We present the instance of two aromatic double bonds and an imine double bond involved thermal 6π‐azaelectrocyclization and, on this basis, a one‐step synthesis of triazacoronenes (TACs) from triphenylene‐1,5,9‐triamines and aldehydes under nonacidic conditions. This method has several advantages such as simplicity, high yields, and extensive substrate scope. A plausible reaction mechanism has been proposed with several experimental supports. A typical derivative shows a unique dimer holding together via a π‐π interaction and six H‐bonds and a zigzag superstructure stabilized by three centered H‐bonds and Br ⋅⋅⋅ π interaction between the adjacent dimers. [ABSTRACT FROM AUTHOR]

A stereoselective synthesis of the bicyclic unit constituting the A and E rings of calyciphylline B-type alkaloids is disclosed. The propionate ester of (1 R)-cyclohex-2-en-1-ol, obtained by enzymatic resolution, is subjected to an Ireland–Claisen rearrangement. Subsequent reduction of the acid, Mitsunobu reaction to introduce a nitrogen functionality, oxidative cleavage to a dialdehyde, and intramolecular aldol and aza-Michael reactions afford the bicyclic subunit. [ABSTRACT FROM AUTHOR]

A new method for the preparation of 2-amino-4(3H)-quinazolinones and similar fused heterocycles is described. Simply warming a mixture of an aryl guanidine and carbonyl diimidazole in acetonitrile results in formation of a putative N -amidinoisocyanate intermediate which undergoes a 6π-electron electrocyclic reaction with the aryl ring to generate the quinazolinone ring system. The mild conditions are compatible with a variety of functional groups, and the reaction is shown to be successful on multigram scale. [ABSTRACT FROM AUTHOR]

cis-2-Butene-1,4-diol was heated with triethyl orthoacetate and p-hydroquinone as catalyst at 170 °C to give racemic Taniguchi lactone. It was converted into diastereomeric amides with (S)-1-phenylethylamine for stereoisomer resolution. The double bonds of (±)-, (R)- and (S)-Taniguchi lactones were brominated and dehydrobrominated in two steps, using at first DBU and then LDA, to deliver the triple bonds. [ABSTRACT FROM AUTHOR]

The treatment of (2-hydroxy-5-oxobicyclo [4.1.0] hept-3-en-3-yl) carbamic acid esters and (2-hydroxy-5-oxobicyclo [4.1.0] hept-3-en-3-yl) benzamide with TMSCl gave 7-membered ring compounds in good yields. The structure of the substituent at the C3 position of the cyclohexene ring is crucial for this ring expansion. The reaction mechanism is thought to involve the formation of a norcaradiene (bicyclo [4.1.0] hept-2,4-diene) structure and subsequent electrocyclic reaction. [ABSTRACT FROM AUTHOR]

A short route toward β-lactams from tolmetin has been developed. In the key step, a ketene was generated on the C-2 of pyrrole ring and reacted with aromatic imines to form trans-β-lactams as the only observed products. The identification of the ketene was confirmed by reaction with the stable free radical TEMPO (TO·). [ABSTRACT FROM AUTHOR]

The kinetics and mechanisms of pyrolysis of 1,3-dihydroisothianaphthene-2,2-dioxide toward benzocyclobutene have been theoretically studied using canonical transition state theory (CTST), statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory, and bonding evolution theory (BET) in conjugation with M06-2X/aug-cc-pVTZ calculations. The CTST slightly breaks down to estimate the reaction rate of the cheletropic extrusion. RRKM results indicated that the cheletropic extrusion and electrocyclic reaction require energy barriers of 171.3 and 122.2 kJ/mol to be overcome; and can be characterized respectively by 7 and 3 phases associated to the sequence of catastrophes C 8 H 8 SO 2 ( 1 ): 7-[FF]C † C † FFF-0: C 8 H 8 + SO 2 and C 8 H 8 ( 2 ): 3-[F † F † ]C-0: C 8 H 8 ( 3 ). For the cheletropic extrusion, breaking of the C 7 –S and C 8 –S bonds begins respectively at Rx = −2.7434 amu 1/2 Bohr and Rx = −1.7458 amu 1/2 Bohr, and formation of the sulfur dioxide is completed at Rx = −0.2494 amu 1/2 Bohr. For the electrocyclic reaction, formation of new C 7 –C 8 bond occurs at Rx = 1.6214 amu 1/2 Bohr from C- to C- coupling between the generated pseudoradical centers at Rx = 0.1474 amu 1/2 Bohr on the terminal carbon atoms. [ABSTRACT FROM AUTHOR]

The detailed mechanism of thermal ring opening reactions of 2 H-pyran and 2 H-1,4-oxazine systems in a broad range of spiropyran and spiro-1,4-oxazine derivatives was studied by density functional methods (PBE0/6-311+G(d,p)). The study revealed mechanistic features and the dependence of activation parameters of this electrocyclic reaction on the steric and electronic properties of spiroconjugated fragments of the studied compounds. [ABSTRACT FROM AUTHOR]

Acceleration of the electrocyclization of 1,3,5-hexatriene to 1,3-cyclohexadiene through early transition metal catalysis is investigated through quantum mechanical methods. The reaction proceeds in a non-pericyclic fashion involving two fundamental steps of catalysis (oxidative addition and reductive elimination), and the calculated acceleration effect is very large, up to 24 kcal mol −1 . Electrocyclization is highly dependent on the nature, formal oxidation state and coordination number of metal. Ligands are also predicted to show tremendous effect on the activation barrier of a reaction. Lowest activation energy is observed for [Nb(CHD)] +3 (5.63 kcal mol −1 ) where Nb is in its highest possible oxidation state i.e. +5. [ABSTRACT FROM AUTHOR]

Conrotatory ring opening of cyclobutene, 3-methoxycyclobutene, and 3-formylcyclobutene has been studied with the density functional theory. The stereoselectivity of these reactions has been elucidated on the basis of the natural bond orbital analysis and correlation diagrams. Hyperconjugative interactions substituent-cyclobutene occurring at the transition state seem to be responsible of these reactions' torquoselectivity. [ABSTRACT FROM AUTHOR]

The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (-F) and donating (-CH 3 ) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multi-reference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and non-adiabatic dynamics suggest that the -CH 3 substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to -F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with -F or -CH 3 , the conversion proceeds via the conrotatory pathway., (© 2022 Wiley-VCH GmbH.)

The structural and electronic properties of a photochromic molecule dictate their potential photochemical activity. To gain insight into these influences, the ground-state structure and excited state properties of six indolylgulgides were calculated using several time dependent-density functional theory (DFT) (TD-DFT)//DFT methods, second-order M⊘ller-Plesset (MP2), and CIS(D). These methods simulated the charge-transfer properties and the conformation of the ground-state structure for each molecule. Generally, TD-DFT accurately simulated the expected charge-transfer state. The degree of spatial overlap of the occupied and virtual molecular orbitals involved in the S1 transition of indolylfulgides quantitatively assessed their charge-transfer character and was qualitatively useful in assessing their photochromic activity. The M06, M06-2X, and M11 structures were quite similar to those calculated by MP2. Structural differences, similarities, and functional trends are compared and discussed. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: 3,10-Dipyrrolidinyl-4,9-methanothia[11]annulene reacts with excess dimethyl acetylenedicarboxylate (DMAD) in refluxing toluene to give ring-enlarged 6,11-methanothia[15]annulene. X-ray crystallographic analysis of the product shows two different cis,trans-dienyl parts in the ring system. Product formation possibly involves π-facial selective addition of the enamine with DMAD and torque-selective ring opening of the intermediate cyclobutenes. [Copyright &y& Elsevier]

Certain organic compounds possess the ability to change color under the influence of light, called photochromism. This change is due to ultrafast chemical transition from open to closed ring isomers (photocyclization), which can be used for optical data storage and photoswitching applications. These applications require minimization of the irreversible photodegradation of the material, called photofatigue. This property is related to the chemical rate of byproduct formation. We use density functional theory methods to predict the mechanism and activation barriers to the byproduct formation for 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene in order to estimate its fatigue resistance. We also explain higher fatigue resistance for its methylated derivative. The methods used in this study may become a part of rational design strategy for the new photochromic materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

New crown-containing and crownless chromenes were synthesized. Their physical properties and photochemistry were characterized. Crown-containing chromenes form inclusion complexes with Mg2+ cation. Two types of photochemical reactions were observed for all the studied chromenes. The photoreaction of the first type is cis–trans isomerization of styryl fragment in closed form. Second type of photoreaction is the reversible formation of open form responsible for the photochromism of chromenes. Arrhenius parameters of back reactions are determined. Both crownless and crown-containing chromenes do not demonstrate cation-dependent photochromism, which is explained by the peculiarities of the structure of open form. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The total synthesis of the 2-azaanthraquinone alkaloid, scorpinone (4), isolated from the mycelium of a Bispora-like tropical fungus, has been completed in nine steps. The two key steps involve a microwave-assisted thermal electrocyclic reaction for the synthesis of an 8-oxygenated isoquinoline skeleton from a 1-aza 6π-hexatriene system, and a regioselective microwave-assisted [4+2] cycloaddition for the construction of a 2-azaanthraquinone framework. [Copyright &y& Elsevier]

Abstract: A novel oxidative photodehydrocyclization of benzothiazolylphenylethenes to a polycyclic heteroaromatic cations with good yields was described. Starting from the trans-derivative, the phototransformation is a multistep process. It includes two photochemical reactions, a trans-cis-isomerization reaction followed by an 1-aza-1,3,5-hexatrienic electrocyclic reaction involving the formation of Che cyclized product gives the stable heteroaromatic cations from hydride elimination with oxygen from air. [Copyright &y& Elsevier]

Abstract: Acyclic conjugated (E,Z,E,E)-tetraenes, upon thermolysis, undergo a domino pericyclic process involving 6π electrocyclisation of the (E,Z,E)-triene moiety to give the corresponding cis-disubstituted 5-vinyl-1,3-cyclohexadienes, followed by an intramolecular Diels–Alder reaction with the vinyl side chain to give tricyclo[3.2.1.02,7]oct-3-enes. [Copyright &y& Elsevier]

Abstract: The reaction of the lithium enolate of 1-benzyl-5-oxo-3-pyrrolidinecarboxylic acid 3 with a series of β-aryl, β-nitroenamines unexpectedly afforded 6-aryl-2-benzyl-4-oxa-1-oxo-3a-methoxycarbonyl-2,5-diazaindenes 9a–d, whose structure was determined by analytical and NMR spectroscopical analysis. The structure of 9b was further confirmed by X-ray analysis. A reasonable mechanism for their formation is given. [Copyright &y& Elsevier]

The transformation of spiroindolinonaphth[2,1-b][1,4]oxazines (SNOs) conjugated with aza-15(18)-crown-5(6) ether moieties or morpholine in the presence of Pb2+ or lanthanoid cations in MeCN solution was studied by UV–Vis, NMR and surface-enhanced resonance Raman scattering spectroscopy methods. The Pb2+ or Eu3+ cations induce the formation of the betaine merocyanine form of SNO. When the merocyanine complexes are kept in the dark, the corresponding oxazole derivatives are formed irreversibly and regioselectively. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highly selective formation of cycloheptene, bicyclo[5.3.0]decadienone, and bicyclo[5.2.0]nonene skeletons from tri- and tetrasubstituted allenynes has been achieved via a Rh(I)-catalyzed ring-closing reaction and proper choice of substrate and/or reaction conditions. [Copyright &y& Elsevier]