Synthesis and Reactivity of Electron-Poor 2-Azadienes. [4 + 2] Cycloaddition Reactions with Alkenes and Enamines

Palacios, Francisco; Heredia, Itziar Perez de; Rubiales, Gloria

doi:10.1021/jo00113a017

Cited by 73 publications

(29 citation statements)

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“…Dihydropyridines 12 were also obtained under catalysis, when the reaction was performed in the presence of lithium perchlorate in a nonaqueous solvent such as diethyl ether (LP‐Et 2 O) at room temperature, similarly to previously reported processes,9c but with a lower yield (Table 1, Entries 8 and 9). Compounds 12 were characterized on the basis of their spectroscopic data, which indicated that they had been isolated as single regioisomers.…”

Section: Resultssupporting

confidence: 65%

Cycloaddition Reactions of Neutral 2-Azadienes with Enamines − Regiospecific Synthesis of Highly Substituted Dihydropyridines and Pyridines

et al. 2001

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2115ization of heterodienes gives pentasubstituted 2,3-dihydropyridines and pyridines in a regioselective fashion.this context, we have been involved in the synthesis of neutral [11] and electron-poor azadienes [9] as well as in the preparation of nitrogen-heterocyclic compounds. [5a,5c,14] As a continuation of our work on the [4ϩ2] cycloaddition chemistry of 2-azadienes, we aim here to explore a new and effective strategy for the preparation of pyridine derivatives through dimerization of electronically neutral 2-azadienes and their reaction with enamines.

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Section: Resultssupporting

confidence: 65%

Cycloaddition Reactions of Neutral 2-Azadienes with Enamines − Regiospecific Synthesis of Highly Substituted Dihydropyridines and Pyridines

et al. 2001

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“…Its vicinal coupling constants ( 3 J H-2,H-7 = 9.3 Hz and 3 J P,C-8 = 11.0 Hz) are consistent with the cis-ring juncture of the fused polycyclic compound [20,21] and with the exo structure in a similar way to that reported for cycloadducts derived from norbornadiene and azides (1,3-cycloadition) [22] or 2-aza-1,3-butadienes (aza-Diels-Alder). [23] This strategy represents the first ex-…”

Section: Resultsmentioning

confidence: 99%

Cycloaddition Reactions of Phosphorylated 1,2‐Diaza‐1,3‐butadienes with Olefins: Regioselective Synthesis of Pyridazine Derivatives

et al. 2005

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The aza‐Diels–Alder reaction of 4‐phosphinyl‐ and 4‐phosphonyl‐1,2‐diaza‐1,3‐butadienes with styrene, cyclopentadiene, dihydrofuran and norbornadiene is reported. Monocyclic, bicyclic and polycyclic tetrahydropyridazines containing a phosphane oxide or a phosphonate substituent are obtained. The formation of cycloadducts can be explained by an endo transition state in the cycloaddition process of these heterodienes with styrene, cyclopentadiene, dihydrofuran, and by means of an exo transition state in the case of norbornadiene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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“…The double bonds of medium‐ring trans ‐alkenes are twisted . trans‐ Cycloalkenes display unusual reactivity in HOMO‐alkene controlled cycloaddition reactions with dienes, 1,3‐dipoles and ketenes . Strained trans‐ cycloalkenes also serve as ligands for transition metals .…”

Section: Figurementioning

confidence: 99%

Flow Photochemical Syntheses of trans‐Cyclooctenes and trans‐Cycloheptenes Driven by Metal Complexation

Pigga

Fox

2019

Israel Journal of Chemistry

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trans-Cyclooctenes and trans-cycloheptenes have long been the subject of physical organic study, but the broader application had been limited by synthetic accessibility. This account describes the development of a general, flow photochemical method for the preparative synthesis of trans-cycloalkene derivatives. Here, photoisomerization takes place in a closed-loop flow reactor where the reaction mixture is continuously cycled through Ag(I) on silicagel. Selective complexation of the trans-isomer by Ag(I) during flow drives an otherwise unfavorable isomeric ratio toward the transisomer. Analogous photoreactions under batch-conditions are low yielding, and flow chemistry is necessary in order to obtain trans-cycloalkenes in preparatively useful yields. The applications of the method to bioorthogonal chemistry and stereospecific transannulation chemistry are described.The unusual reactivity and well-defined chiral structure of trans-cycloalkenes has made them attractive targets for synthesis for nearly 70 years. [1][2][3] For example, trans-cyclooctene possesses planar chirality and displays a high barrier to racemization (E a = 35.6 kcal/mol), [4] and the most stable "crown" conformer has an alternating sequence of equatorial and axial hydrogens that is akin to chair cyclohexane. [5][6] The double bond of trans-cyclooctene is twisted severely in the crown conformation, [7] and as a consequence the HOMO of trans-cyclooctene is relatively high in energy. [8] trans-Cycloheptene also has a rigid structure with a distorted alkene. [7] The double bonds of medium-ring trans-alkenes are twisted. [7] trans-Cycloalkenes display unusual reactivity in HOMOalkene controlled cycloaddition reactions with dienes, [9] 1,3dipoles [8] and ketenes. [10] Strained trans-cycloalkenes also serve as ligands for transition metals. [11][12][13][14][15][16] This reactivity profile has made trans-cycloalkanes interesting targets for applications in synthesis and biology.The broadest applications of trans-cycloalkenes are in the field of bioorthogonal chemistry. The inverse-electron demand Diels-Alder reaction between tetrazines and strained alkenes has a rich history in physical organic and synthetic chemistry (Figure 1). [17][18][19] In 2008, three groups described the bioorthogonal reactions of tetrazines with strained alkenes. [20][21][22] The variant introduced by our group that used trans-cyclooctene is marked by exceptionally rapid kinetics, with rate constants that can exceed 10 6 M À 1 s À 1 in the fastest cases. [23][24] With the advances including the development of fluorogenic tetrazines [25] and reactions in live cells [26] and animals, [27] the tetrazine ligation has become a widely used tool for applications that span chemical biology, biomedical imaging, and materials science. [28][29][30][31][32][33][34][35][36][37] This account describes the development of general, flow photochemical methods for the preparative synthesis of transcycloalkene derivatives and enabled applications in synthesis and bioorthogonal chemistry. Selectiv...

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Synthesis and Reactivity of Electron-Poor 2-Azadienes. [4 + 2] Cycloaddition Reactions with Alkenes and Enamines

Cited by 73 publications

References 1 publication

Cycloaddition Reactions of Neutral 2-Azadienes with Enamines − Regiospecific Synthesis of Highly Substituted Dihydropyridines and Pyridines

Cycloaddition Reactions of Neutral 2-Azadienes with Enamines − Regiospecific Synthesis of Highly Substituted Dihydropyridines and Pyridines

Cycloaddition Reactions of Phosphorylated 1,2‐Diaza‐1,3‐butadienes with Olefins: Regioselective Synthesis of Pyridazine Derivatives

Flow Photochemical Syntheses of trans‐Cyclooctenes and trans‐Cycloheptenes Driven by Metal Complexation

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