Sequential Pericyclic Reactions Research Articles

Cyclic Alkyne Approach to Heteroatom‐Containing Polycyclic Aromatic Hydrocarbon Scaffolds

AbstractWe report a modular synthetic strategy for accessing heteroatom‐containing polycyclic aromatic hydrocarbons (PAHs). Our approach relies on the controlled generation of transient heterocyclic alkynes and arynes. The strained intermediates undergo in situ trapping with readily accessible oxadiazinones. Four sequential pericyclic reactions occur, namely two Diels–Alder/retro‐Diels–Alder sequences, which can be performed in a stepwise or one‐pot fashion to assemble four new carbon–carbon (C−C) bonds. These studies underscore how the use of heterocyclic strained intermediates can be harnessed for the preparation of new organic materials.

Cyclic Alkyne Approach to Heteroatom-Containing Polycyclic Aromatic Hydrocarbon Scaffolds.

We report a modular synthetic strategy for accessing heteroatom-containing polycyclic aromatic hydrocarbons (PAHs). Our approach relies on the controlled generation of transient heterocyclic alkynes and arynes. The strained intermediates undergo in situ trapping with readily accessible oxadiazinones. Four sequential pericyclic reactions occur, namely two Diels-Alder/retro-Diels-Alder sequences, which can be performed in a stepwise or one-pot fashion to assemble four new carbon-carbon (C-C) bonds. These studies underscore how the use of heterocyclic strained intermediates can be harnessed for the preparation of new organic materials.

Mechanistic Studies on the Rearrangement of a Boron Cation: From a nido-Carborane to a Planar Boracycle

The reaction mechanism of the [Et3BH]−-induced conversion of a dicationic boron compound ([Cp*B-IMes]2+, [1]2+) to a planar neutral carbene-coordinated borabenzene (2) is investigated experimentally and theoretically. Owing to the steric congestion around the boron center, bulky [Et3BH]− attacks the less encumbered carbon atom of Cp*, leading to a metastable 5-borabicyclo[2.1.1]hex-2-ene borenium cation ([3-CH]+) at low temperature. Upon raising the temperature, the bicyclic-borenium ion undergoes sequential pericyclic reactions, including suprafacial [1,3]-sigmatropic shift, two-electron electrocyclic ring opening, and then [1,2]-hydrogen shift to a planar cyclic borenium ion, [4-CH]+, which can then be deprotonated to yield the neutral aromatic borabenzene. The attack of hydride at the boron center of [1]2+ was excluded through the preparation and isolation of 6-borabicyclo[3.1.0]hexenylium, [3-BH]+, which could not be transformed into [3-CH]+ or [4-CH]+. The borenium ion rearrangement follows first-order kinetics with activation parameters of ΔH⧧ = 19.6 (±0.31) kcal/mol and ΔS⧧ = −2.03 (±1.15) cal/mol·K. The observed kinetic isotope effect of 0.87 at 265 K is consistent with the DFT-calculated reaction mechanism, which predicts an overall KIE value of 0.90. These results show that [1]2+ reacts with [Et3BH]− as a carbon-based electrophile and the formation of an electron-deficient borenium center is responsible for the skeletal rearrangement of the nido-cluster.

An Atom‐Economical and Stereoselective Domino Synthesis of Functionalised Dienes

Open sesame: A direct synthesis of functionalised and stereodefined dienes, relying on a domino allylic alkylation/electrocyclic ring-opening sequence, is reported. This method allows concise access to doubly vinylogous esters. A further systematic study of ring-opening rates of carbon-substituted cyclobutenes allowed the design of substrates amenable to sequential pericyclic reactions (see scheme).

Sequential pericyclic reaction of ene-diallene: synthesis of (±)-estrone

The one-pot construction of perhydrophenanthrene from an acyclic substrate was achieved via a sequential pericyclic reaction, which involved the in situ generation of ene-diallene species due to Myers' propargyl alcohol–allene transformation. The resulting perhydrophenanthrene derivative could be successfully converted into (±)-estrone.

Sequential Pericyclic Reaction of Ene-diallenes: An Efficient Approach to the Steroid Skeleton

[reaction: see text] The one-pot construction of polycyclic aromatic systems from acyclic ene-bis(propargyl alcohols) was achieved through a tandem dual [2,3]-sigmatropic rearrangement/6pi-electrocyclic reaction/intramolecular [4 + 2] cycloaddition sequence. A steroidal compound was conveniently synthesized using the present method.

Cyclopentadienone類とpropargylamine及びalcohol 類との連続反応：付加体の構造と反応機構

Cyclopentadienone類とpropargylamine及びalcohol 類との連続反応：付加体の構造と反応機構

Another Aspect of the Reaction Behavior of Cyclopentadienones: 1,5‐Sigmatropic Rearrangement of the 1,4‐Addition Products of Amines

AbstractTreatment of 2,5‐bis(methoxycarbonyl)‐3,4‐diphenylcyclopentadienone (1) with aniline (2a) gave the stereoisomeric 2‐anilino‐2,5‐bis(methoxycarbonyl)‐3,4‐diphenylcyclopentenones (cis‐ and trans‐4a). 1H NMR spectroscopic monitoring of the reaction indicates that both compounds are derived from the 1,5‐sigmatropic rearrangement of the 1,4‐addition products cis‐ and trans‐3a. The structure of 3a was established by the X‐ray analysis of the product after methylation (3a‐Enol‐Me) with diazomethane. The sequential pericyclic reaction behavior of 1 with amines is discussed on the basis of X‐ray crystal structures and the optimized structure of the transition state at the B3LYP/6−31G(d) level of theory. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The Ester Dienolate [2,3]‐Wittig Rearrangement — Development, Opportunities, and Limitations.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Ester Dienolate [2,3]-WittigRearrangement - Development, Opportunities, andLimitations

The account summarizes the development of the ester dienolate [2,3]-Wittig rearrangement as a versatile synthetic tool for the construction of highly substituted 3-alkoxycarbonyl-3-hydroxy-substituted 1,5-hexadienes. Furthermore, the account provides an insight into a novel sequential pericyclic reaction employing the 1,5-hexadienes accessible through the ester dienolate [2,3]-Wittig rearrangement.

Cyclopentadienone 類と不飽和アミン、アルコールとの連続周辺環状反応

Cyclopentadienone 類と不飽和アミン、アルコールとの連続周辺環状反応

Cyclization of electron-deficient cyclopentadienone with 2-alkenyl and 2-alkynylamines via sequential pericyclic reaction pathway.

The pericyclic reactions of 2,5-bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1a) with both allylic and propargylic amines have been investigated. The reaction proceeded via initial formation of the 1,4 adducts followed by the ene cyclization and/or sequential pericyclic reactions depending upon the structures of the amines. The reaction of 1a with diallylamine (2a) gave the tetracyclic compound (3a). On the other hand, the reaction of 1a with 2-propynylamine (2c) gave exclusively the bicyclic compound (5c). In the reactions with the secondary 2-propynylamines (2d,e), the tetracyclic compounds (3d,e) were exclusively formed. The reactions of 1a with alpha-branched primary 1,1-dialkyl-2-propynylamines (2f,g) gave mixtures of 3- and 5-type compounds. The tetracyclic compounds 3 were formed from the intramolecular [4+2]pi cycloadditions of the [1,5]-sigmatropic rearrangement products of the 1,4 adducts of 1a and 2, followed by the [1,5]-sigmatropic rearrangement of hydrogen and dehydrogenation. The bicyclic compounds 5 were derived from the [2pi+2pi+2sigma] reaction of the 1,4 adducts of 1a and 2. The one-pot multistage sequential pericyclic reactions were discussed on the basis of the X-ray crystallographic structures and the MO calculation data.

Ab initio study of formation and structure of double Diels-Alder cycloadduct derived from sequential pericyclic reactions of 2-pyrone with cycloocta-1,5-diene

Molecular orbital calculations were carried out to interpret the reaction behavior of the formation reaction and structural feature of double Diels-Alder (DDA) adduct derived from three-step sequential pericyclic reactions of 2-pyrone with cycloocta-1,5-diene. The experimental results are correctly predicted by the ab initio calculations at the 3-21G level.

ChemInform Abstract: Sequential Pericyclic Reaction of Unsaturated Xanthates. Intramolecular Cycloaddition Selectivity of the 2,4‐Alkadienyl 2‐ Alkenyl Sulfides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Pericyclic Reaction Behavior of Cyclopentadienones toward Acyclic Conjugated Dienes. (3,3)-Sigmatropic Rearrangement and Double Diels-Alder Reactions of the endo(4+2).PI. Cycloadducts.

Cycloaddition of 2, 5-disubstituted-3, 4-diphenylcyclopentadienone with acyclic conjugated dienes gave the endo [4+2]π cycloadducts, which then underwent [3, 3]-sigmatropic rearrangement to give the corresponding endo [2+4]π cycloadduct on heating at 110°C. Pyrolysis of the endo [4+2]π cycloadducts at 170°C resulted in decarbonylation to give the double Diels-Alder adduct. The sequential pericyclic reaction behavior is discussed on the basis of X-ray diffraction analyses and molecular orbital calculation data.

Sequential pericyclic reaction of unsaturated xanthates. Intramolecular cycloaddition selectivity of the 2,4-alkadienyl 2-alkenyl sulfides

Heating of S-(1-vinyl-2-alkenyl) S-(2-alkenyl or alkynyl) dithiocarbonates (dithiolcarbonates) derived from [3,3]-sigmatropic rearrangement of O-(2,4-alkadienyl) S-(2-alkenyl or alkynyl) dithiocarbonates (xanthates) gave the 2,4-alkadienyl 2′-(alkenyl or alkynyl) sulfides, which then underwent intramolecular Diels-Alder cycloaddition to give hydrobenzo[c]thiophene derivatives. The thermal cyclizations of O-(2,4-pentadienyl) derivatives of xanthate afforded mixtures of the cycloadducts, in which the cis-FUSED products slightly predominated over the trans-isomers. The selectivity of IMDA reactions is discussed based on the ab initio calculation data.

Reaction of Aromatic N-Oxides with Dipolarophiles XIX. PM3 Analysis of Sequential Pericyclic Reactions between Pyridine N-Oxides and Allenes

Sequential pericyclic reactions between pyridine N-oxides and allenes were evaluated in terms of PM3 calculation. Structures corresponding to the perturbating system were calculated by varying the distance of the addends. The cycloaddition occurs via π-complex. In the transition structure TS1 of primary cycloaddition, the lengths of the newly created bonds of O-C and C-C are 1.864 and 2.204 A, respectively. The bond between the O atom of pyridine N-oxide and the central carbon of allene is ca. 35% formed at TS1, slightly advanced than the other (ca. 30%). The PM3 calculation at the UHF level predicts that [1,5]-sigmatropic rearrangement of the primary cycloadduct proceeds via a transition state with a biradical character

Sequential pericyclic reactions of cyclopentadienone with nonconjugated dienes. Intramolecular cycloaddition reactivity of the decarbonylated primary cycloadducts and X-ray structure of DDA adduct

Pericyclic reactions of 2-oxo-1,3-bis(ethoxycarbonyl)-2 H-cyclopenta[ a]acenaphthylene ( 1b) with nonconjugated dienes ( 2c-k) were investigated. The cyclopentadienone ( 1b) reacted readily with 2c-k to give [4+2]π cycloadducts ( 3c-k) that spontaneously lost carbon monoxide to afford the dihydrohexadiene derivatives ( 4), some of which underwent intramolecular cycloaddition reaction to give the double Diels-Alder reaction (DDA) cycloadducts ( 5). The structures of 4 and 5 were determined from spectral data. The intramolecular cycloaddition reactivity of 4 are discussed on the basis of the MNDO-PM3 calculated transition states. The structure of the DDA cycloadduct from 1 and dibenzo [ a, c]cyclooctadiene was determined by single crystal X-ray analysis, indicating the presence of moderate bond elongations due to through-bond interaction. The observed data were compared with those derived from the MM and MO-calculated structures.

ChemInform Abstract: Sequential Pericyclic Reactions of Unsaturated Xanthates. One‐Pot Synthesis of Hydrobenzo(c)thiophenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reaction of aromatic N-oxides with dipolarophiles. Part 18. Formation mechanism and X-ray structure of the cycloadduct from sequential pericyclic reaction of pyridine N-oxides with phenylsulfonylallene

Sequential pericyclic reactions of pyridine N-oxides (1) with phenylsulfonylpropadiene (2) and 1-phenylsulfonylpropyne (3) were investigated. 3,5-Dimethylpyridine N-oxide (la) was allowed to react with 2 in CHCl3 at room temperature to give a mixture of the [1,5]-sigmatropic rearrangement product (4a) of the 1 : 1 cycloadduct and the 1 : 2 azetidine-type cycloadduct (5a). The structure of 5a was established by single crystal X-ray analysis. The reaction rate of 1a with 2 was about 50 000 times that of 1a with N-phenylmaleimide. The reaction of 1a with 3 did not give 5a but 4a as the sole product. The reactivity, regio- and peri-selectivity and formation mechanism of 4 and 5 are discussed in terms of the frontier molecular orbital consideration based on kinetic and molecular orbital calculation data.