Search results for "Diels–Alder reaction"

A study of the diels-alder reaction of 3-oxabicyclo[3.3.0]oct-1(5)-ene-2,4-dione with cyclopentadiene and some related dienes

1984

Abstract The reaction of 3-oxabicyclo[3.3.0]oct-l(5)ene-2,4-dione, 2, with cyclopentadiene, 3, 5,5-diethoxycyclopentadiene, 4, and 6,6-dimethylfulvene, 5, is studied. Reaction of 2 and 3 yields the expected endo-adduct, while reaction of 2 and 5 gives a mixture of the endo- and exo-adducts whose ratio is slightly dependent on the reaction conditions. Attractive electrostatic interactions in the transition state leading to the exo-adduct can explain the absence of endo stereoselectivity in the last reaction. Steric factors seem to be responsible for the absence of reaction between 2 and 4. The analysis of the 13C NMR spectra of these adducts and some derived compounds confirms the tentative …

Asymmetric synthesis of bicyclic amino acid derivatives by Aza-Diels-Alder reactions in aqueous solution

1991

Derivatives 7–10 and 13–16 of methyl and ethyl 2-azabicyclo[2.2.1]heptane-3-carboxylates are synthesized by Aza-Diels-Alder reactions of chiral iminium ions, formed in situ from glyoxylic acid and chiral amines, with cyclopentadiene. Whereas the heterodienophiles derived from phenylglycinol and esters of sterically more demanding amino acids fail to undergo asymmetric cycloadditions, with alanine methyl ester and (R)-1-phenylethylamine hydrochoride the cycloadducts are formed in yields of 15 and 52%, respectively, reaching de values of up to 90:10 for the exo isomers.

Synthetic studies on the preparation of oxygenated spongiane diterpenes from carvone

2003

Abstract The paper describes a new diastereoselective approach to oxygenated spongiane diterpenes functionally related to natural dorisenones. The strategy followed for the preparation of the spongiane framework, a B→AB→ABC→ABCD approach, is based on the preparation of epoxydecalone 11 (AB rings) from R-(−)-carvone, followed by an intramolecular Diels–Alder reaction for the construction of the C ring (compound 26 ). Further manipulation of the Diels–Alder adduct functionality allows the completion of the spongiane framework and the elaboration of several oxygenated spongiane-type compounds. The structures of two compounds 27 and 31 , has been established by single-crystal X-ray crystallogra…

Ionic liquid binary mixtures: How different factors contribute to determine their effect on the reactivity

2016

We studied how mixing ionic liquids affected the rate of the Diels Alder reaction between 9-anthracenemethanol and N-ethylmaleimide. The mixtures considered spanned the whole compositional range and differed for the anion or the cation. These comprised mixtures of the ionic liquid 1-benzyl-3-butyl-imidazolium bis-(trifluoromethanesulfonyl)imide ([Bzbim][NTf2]) with 1-(2,3,4,5,6-pentafluorophenyl)-3-butyl-imidazolium bis-(trifluoromethanesulfonyl)imide ([Bz(F5)bim][NTf2]) or 1-benzyl-3-butyl-imidazolium tetrafluoroborate ([Bzbim][BF4]). Moreover we studied the reaction in a set of mixtures containing an aliphatic and an aromatic cation, namely [Bzbim+] and N-butyltriethylammonium ([bEt3N+]) …

Modular Assembly of Multimodal Imaging Agents through an Inverse Electron Demand Diels–Alder Reaction

2019

International audience; The combination of two imaging probes on a same biomolecule gives access to targeted bimodal imaging agents that can provide more accurate diagnosis, complementary information, or that may be used in different applications, such as PET imaging and fluorescence imagingassisted surgery. In this study, we demonstrate that dichlorotetrazine, a small, commercially available compound, can be used as a modular platform to easily assemble various imaging probes. Doubly-labeled tetrazines can then be conjugated to a protein through a biorthogonal IEDDA reaction. A series of difunctionalized tetrazine compounds containing various chelating agents and fluorescent dyes was synth…

Lithium Cation-Catalyzed Benzene Diels-Alder Reaction: Insights on the Molecular Mechanism Within the Molecular Electron Density Theory.

2020

The lithium cation Li+-catalyzed Diels-Alder (DA) reactions of benzene toward a series of acetylenes of improved nucleophilicity can be described within the context of the molecular electron density theory (MEDT) at the ωB97XD/6-311G(d,p) level. Conceptual density functional theory indices characterize the crown ether solvated complex benzene-lithium Bz-Li-Cro as a superelectrophile. Coordination of a lithium cation to benzene does not change substantially the electron localization function electronic structure of benzene. The DA reaction of Bz-Li-Cro with acetylene shows a reduction of the energy of activation of 6.9 kcal·mol-1, which is not sufficient for the reaction to take place, thus …

1990

An AM1 theoretical study on the effect of Zn2+ Lewis acid catalysis on the mechanism of the cycloaddition between 3-phenyl-1-(2-pyridyl)-2-propen-1-o…

2002

Abstract The mechanism of the Diels–Alder reaction between 3-phenyl-1-(2-pyridyl)-2-propen-1-one and cyclopentadiene has been investigated with the AM1 semiempirical method. Stationary points for two reactive channels, endo - cis and exo - cis , have been characterized. The role of the Lewis acid catalyst has been modeled taking into account the formation of a complex between Zn 2+ and the carbonyl oxygen atom and the pyridyl nitrogen atom of the 3-phenyl-1-(2-pyridyl)-2-propen-1-one system with and without the presence of two molecules of water around the cation. The mechanism of the uncatalyzed reaction corresponds to a concerted process, but in the presence of Lewis acid catalyst the mec…

Application of Furan as a Diene: Preparation of Condensed 1,3-Oxazines by Retro-Diels−Alder Reactions

2004

(Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-en-2-yl)methanol (3) was treated with oxo carboxylic acids [p-toluoylpropionic acid, cis- or trans-(p-toluoyl)cyclohexanecarboxylic acid, -benzoic acid or methanobenzocyclooctenecarboxylic acid] to furnish the oxanorbornene-fused pyrrolo[1,3]oxazine 4, the isoindolo[1,3]oxazines 5 and 6, and the methanobenzocyclooctenepyrrolo[1,3]oxazine 10, together with the retro-Diels−Alder products pyrrolooxazinone 7, oxazinoisoindolones 8 and 9, and oxazinopyrrolobenzocyclooctene 11. On reflux in chlorobenzene, furan was released from the oxanorbornene heterocycles 5 and 10 to give the retro-Diels−Alder products. The structures of the new compounds were establi…

Stereoselective synthesis of polyoxygenated atisane-type diterpenoids

2001

Abstract A new stereoselective approach to polyoxygenated atisane-type diterpenes starting from (S)-(+)-carvone is described. The key steps involve an intramolecular Diels–Alder reaction, an unusual intramolecular diazo ketone cyclopropanation of an unsaturated ketone, and a regioselective endocyclic cleavage of a cyclopropyl carbinyl radical as key synthetic steps. The synthesis of the bioactive polyoxygenated atisanes atis-16(17)-en-3,14-dione ( 2 ) and 3R-hydroxy-atis-16(17)-en-2,14-dione ( 3 ) following this approach is presented.