Zur kinetik der conrotatorischen valenzisomerisierung von stereoisomeren decatetraenen

Huisgen, Rolf; Dahmen, Alexander; Huber, Helmut

doi:10.1016/s0040-4039(01)87914-4

Cited by 32 publications

(9 citation statements)

References 4 publications

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“…The reactions of substrates 5 and 6 correspond to reactions involved in the biosyntheses of the endiandric acid and kinginian families of natural products. The 8π electrocyclization of tetraene 5 proceeds with a Δ H ⧧ 298.15K of 15.1 kcal mol –1 , 24 similar to the computed value of 14.4 kcal mol –1 (Figure 4 ). In the case of the 8π electrocyclization of 6 , the computed value of Δ H ⧧ 298.15K of 17.6 kcal mol –1 is at variance with the experimental value 24 of 21.8 kcal mol –1 by approximately 4 kcal mol –1 .…”

Section: Resultssupporting

confidence: 82%

Terminal Substituent Effects on the Reactivity, Thermodynamics, and Stereoselectivity of the 8π–6π Electrocyclization Cascades of 1,3,5,7-Tetraenes

Patel

Houk

2014

J. Org. Chem.

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M06-2X/6-31+G(d,p) computations are reported for the 8π–6π electrocyclization cascades of 1,3,5,7-tetraenes. The rate-determining step for these cascades is typically the second (6π) ring closure. According to experiment and theory, un- and monosubstituted tetraenes readily undergo 8π electrocyclic ring closure to form 1,3,5-cyclooctatrienes; however, the 6π electrocyclizations of these cyclooctatriene intermediates are slow and reversible, and mixtures of monocyclic and bicyclic products are formed. Computations indicate that di- and trisubstituted tetraenes undergo facile but less exergonic 8π electrocyclization due to a steric clash that destabilizes the 1,3,5-cyclooctatriene intermediates. Relief of this steric clash ensures the subsequent 6π ring closures of these intermediates are both kinetically facile and thermodynamically favorable, and only the bicyclic products are observed for the cascade reactions of naturally occurring tri- and tetrasubstituted tetraenes (in agreement with computations). The 6π electrocyclization step of these cascade electrocyclizations is also potentially diastereoselective, and di- and trisubstituted tetraenes often undergo cascade reactions with high diastereoselectivities. The exo mode of ring closure is favored for these 6π electrocyclizations due to a steric interaction that destabilizes the endo transition state. Thus, theory explains both the recalcitrance of the unsubstituted 1,3,5,7-octatetraene and 1-substituted tetraenes toward formation of the bicyclo[4.2.0]octa-2,4-diene products, as well as the ease and the stereoselectivity with which terminal di- and trisubstituted tetraenes are known to react biosynthetically.

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Section: Resultssupporting

confidence: 82%

Terminal Substituent Effects on the Reactivity, Thermodynamics, and Stereoselectivity of the 8π–6π Electrocyclization Cascades of 1,3,5,7-Tetraenes

Patel

Houk

2014

J. Org. Chem.

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“…This indicates that the pericyclic cascades could already occur on a shorter intermediate, such as 8 , within the chiral environment of a molecular assembly line (Scheme D) . The cyclization of an intermediate bound to a polyketide synthase‐nonribosomal peptide synthetase (PKS‐NRPS) via a thioester could also explain why interception of the cyclooctadiene 9 in a Diels–Alder reaction to afford 10 is favored over a relatively fast 6π electrocyclization, which is essentially irreversible at ambient temperatures …”

Section: Methodsmentioning

confidence: 99%

“…[10,11] The cyclization of an intermediate bound to a polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) via a thioester could also explain why interception of the cyclooctadiene 9 in a Diels-Alder reaction to afford 10 is favored over a relatively fast 6p electrocyclization, which is essentially irreversible at ambient temperatures. [12][13][14][15] Given these considerations, a biomimetic laboratory synthesis of PF-1018 poses considerable challenges. We have previously developed an 8p electrocyclization/Diels-Alder cascade that gave rise to the partially saturated tricyclic core of PF-1018.…”

mentioning

confidence: 99%

Bioinspired Synthesis of (−)‐PF‐1018

et al. 2020

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The combination of electrocyclizations and cycloadditions accounts for the formation of a range of fascinating natural products. Cascades consisting of 8π electrocyclizations followed by a 6π electrocyclization and a cycloaddition are relatively common. We now report the synthesis of the tetramic acid PF‐1018 through an 8π electrocyclization, the product of which is immediately intercepted by a Diels–Alder cycloaddition. The success of this pericyclic cascade was critically dependent on the substitution pattern of the starting polyene and could be rationalized through DFT calculations. The completion of the synthesis required the instalment of a trisubstituted double bond by radical deoxygenation. An unexpected side product formed through 4‐exo‐trig radical cyclization could be recycled through an unprecedented triflation/fragmentation.

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“…However running the reaction in CH2C12 at 20 "C both possible reaction pathways are realized furnishing 1Sb (yield 41 %) as well as the cage compound 19b (yield 37%) [7a]. tomeric equilibria between cycloocta-l,3,5-triene (23), and all-cis-octa-1,3,5,7-tetraene (23a) on the one hand and between 23 and bicyclo[4.2.0]octa-2,4-diene (23b) on the other hand [8].…”

mentioning

confidence: 99%

Pericyclic Domino reactions with 3,6-Bis(trifluoromethyl)-1,2,4,5-tetrazine: A convenient entry into azo cage compounds

et al. 1997

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3,6‐Bis(trifluoromethyl)‐1,2,4,5‐tetrazine (1) characterized by a highly reactive, electron deficient diazdiene system reacted with several cyclic and acyclic bis‐dienophiles to yield the cage compounds 11, 19a, b, 31a, b and 41 in a pericyclic homo‐domino reaction in good yields. The first step of the domino reactions is an inverse electron demand inter‐molecular Diels–Alder addition followed by elimination of nitrogen to give 4,5‐dihydropyridazines which then undergo a terminal ring closure to yield the cage compounds. The solvent employed and the reaction temperature is of crucial importance. Whereas in nitromethane and at elevated temperatures the main products are the cage compounds, at lower temperature and in dichloromethane as solvent the initially formed 4,5‐dihydropyridazines are frequently converted to 1,4‐dihydropyridazines by a 1,3‐H‐shift. Treatment of the tetrazine 1 with cyclooctatriene 23 did not lead to a cage compound in any case; instead via valence tautomeric species octa‐1,3,5,7‐tetraene 23a and bicyclo[4.2.0]octa‐2,4‐diene 23b the twofold pyridazine‐substituted butadienes 24 and 26 together with the tricyclic cyclobuta[f]phthalazine 25 were formed.

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Zur kinetik der conrotatorischen valenzisomerisierung von stereoisomeren decatetraenen

Cited by 32 publications

References 4 publications

Terminal Substituent Effects on the Reactivity, Thermodynamics, and Stereoselectivity of the 8π–6π Electrocyclization Cascades of 1,3,5,7-Tetraenes

Terminal Substituent Effects on the Reactivity, Thermodynamics, and Stereoselectivity of the 8π–6π Electrocyclization Cascades of 1,3,5,7-Tetraenes

Bioinspired Synthesis of (−)‐PF‐1018

Pericyclic Domino reactions with 3,6-Bis(trifluoromethyl)-1,2,4,5-tetrazine: A convenient entry into azo cage compounds

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