Theoretical Prediction and Experimental Tests of Conformational Switches in Transition States of Diels−Alder and 1,3-Dipolar Cycloadditions to Enol Ethers

1998 ◽  
Vol 63 (4) ◽  
pp. 1064-1073 ◽  
Author(s):  
Jian Liu ◽  
Satomi Niwayama ◽  
Ying You ◽  
K. N. Houk
Keyword(s):  
Theoretical Prediction ◽  
Transition States ◽  
Experimental Tests ◽  
Diels Alder ◽  
Enol Ethers ◽  
Dipolar Cycloadditions ◽  
Conformational Switches

Synthese neuer Pyridin-C-nukleoside der 2 ,3 -Didesoxyribose durch „inverse“ [4+2]-Cycloaddition Synthesis of Novel Pyridine-C-nucleosides of 2,3-Dideoxyribose by „Inverse“ [4+2]-Cycloaddition

1997 ◽  
Vol 52 (7) ◽  
pp. 851-858 ◽  
Author(s):  
Gunther Seitz ◽  
Johanna Siegl
Keyword(s):  
Cycloaddition Reaction ◽  
Alder Reaction ◽  
Diels Alder ◽  
The Novel ◽  
Protecting Group ◽  
Enol Ethers ◽  
Inverse Electron Demand ◽  
Diels Alder Reaction ◽  
Cyclic Ketene Acetals

The anomeric imido esters 5 and 6, appropriate precursors for C-nucleoside synthesis, were prepared and utilized as heterodienophiles in a Diels-Alder reaction with inverse electron demand to yield the novel, protected 1.2.4-triazine C-nucleosides 8 and 9. They could be deprotected by treatment with 70% trifluoroacetic acid to furnish the free C-nucleosides 10 and 11. The triazine „aglycon“ of 8 contains an electron deficient diazadiene system, highly activated to react with various electron rich dienophiles such as enamines, enol ethers and several cyclic ketene acetals in an „inverse“ [4+2]-cycloaddition reaction. The Diels-Alder adducts spontaneously eliminate N2 and after follow-up reactions the O-TBDPS protected pyridine-C-nucleosides 13, 15, 17,19, 21 and 23 are formed. Removal of the protecting group by treatment with CF3CO2H /H2O leads to the corresponding 2’,3’-dideoxy-β-D-ribofuranosyl- pyridines.

Advances in Alkene and Alkyne Metathesis

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Acetic Acid ◽  
Diels Alder ◽  
Alkyne Metathesis ◽  
Santa Barbara ◽  
Ring Closing Metathesis ◽  
Enol Ethers ◽  
Cross Metathesis ◽  
Simple Filtration ◽  
The University ◽  
Academy Of Sciences

As alkene metathesis is extended to more and more challenging substrates, improved catalysts and solvents are required. Robert H. Grubbs of Caltech developed (Organic Lett. 2008, 10, 441) the diisopropyl complex 1, that efficiently formed the trisubstituted alkene 6 by cross metathesis of 4 with 5. Hervé Clavier and Stephen P. Nolan of ICIQ, Tarragona, and Marc Mauduit of ENSC Rennes found (J. Org. Chem. 2008, 73, 4225) that after cyclization of 7 with the complex 2b, simple filtration of the reaction mixture through silica gel delivered the product 8 containing only 5.5 ppm Ru. The merit of CH2Cl2 as a solvent for alkene metathesis is that the catalysts (e.g. 1 - 3) are very stable. Claire S. Adjiman of Imperial College and Paul C. Taylor of the University of Warwick established (Chem. Commun. 2008, 2806) that although the second generation Grubbs catalyst 3 is not as stable in acetic acid, for the cyclization of 9 to 10 it is a much more active catalyst in acetic acid than in CH2Cl2 . Bruce H. Lipshutz of the University of California, Santa Barbara observed (Adv. Synth. Cat . 2008, 350, 953) that even water could serve as the reaction solvent for the challenging cyclization of 11 to 12, so long as the solubility- enhancing amphiphile PTS was included. Ernesto G. Mata of the Universidad Nacional de Rosario explored (J. Org. Chem. 2008, 73, 2024) resin isolation to optimize cross-metathesis, finding that the acrylate 13 worked particularly well. Karol Grela of the Polish Academy of Sciences, Warsaw optimized (Chem. Commun. 2008, 2468) cross-metathesis with a halogenated alkene 16. Jean-Marc Campagne of ENSC Montpellier extended (J. Am. Chem. Soc. 2008, 130, 1562) ring-closing metathesis to enynes such as 19. The product diene 20 was a reactive Diels-Alder dienophile. István E. Markó of the Université Catholique de Louvain applied (Tetrahedron Lett. 2008, 49, 1523) the known (OHL 20070122) ring-closing metathesis of enol ethers to the cyclization of the Tebbe product from 23. The ether 24 was oxidized directly to the lactone 25.

Synthesis of Siloxy-α-Lapachone Derivatives by Chemo- and Regioselective Diels-Alder Reactions of 3-Methylene-1,2,4-naphthotriones with Silyl Enol Ethers

Synthesis ◽  
2008 ◽  
Vol 2008 (8) ◽  
pp. 1182-1192 ◽  
Author(s):  
Jian-Hua Xu ◽  
Da-Quan Peng ◽  
Yun Liu ◽  
Zhi-Feng Lu ◽  
Yong-Miao Shen
Keyword(s):  
Diels Alder ◽  
Enol Ethers ◽  
Silyl Enol Ethers

Hetero-Diels–Alder Reaction of Phosphorylated Nitroso Alkenes with Enol Ethers on Water: A Clean Approach Toward 1,2-Oxazine Derivatives

2014 ◽  
Vol 79 (16) ◽  
pp. 7607-7615 ◽  
Author(s):  
Jesús M. de los Santos ◽  
Roberto Ignacio ◽  
Zouhair Es Sbai ◽  
Domitila Aparicio ◽  
Francisco Palacios
Keyword(s):  
Alder Reaction ◽  
Diels Alder ◽  
Enol Ethers ◽  
Diels Alder Reaction ◽  
Oxazine Derivatives

scholarly journals Domino reactions in the synthesis of heterocyclic natural products and analogs

2004 ◽  
Vol 76 (11) ◽  
pp. 1967-1983 ◽  
Author(s):  
L. F. Tietze ◽  
N. Rackelmann
Keyword(s):  
Alder Reaction ◽  
Diels Alder ◽  
Domino Reactions ◽  
Complex Molecules ◽  
Enol Ethers ◽  
Dicarbonyl Compound ◽  
Bond Forming ◽  
Enantioselective Total Synthesis ◽  
Subsequent Transformation ◽  
Diels Alder Reaction

Domino reactions are defined as processes of two or more bond-forming reactions under identical conditions, in which the subsequent transformation takes place at the functionalities obtained in the former transformation. They allow the efficient synthesis of complex molecules from simple substrates in an ecologically and economically favorable way. A very powerful domino process is the domino Knoevenagel–hetero-Diels–Alder reaction, in which an aldehyde or an beta-ketoester is condensed with a 1,3-dicarbonyl compound or a heteroanalog to give a 1-oxa-1,3-butadiene, which can undergo an inter- or intramolecular hetero-Diels–Alder reaction with dienophiles such as enol ethers or alkenes. The products are dihydropyrans, which can be transformed in a variety of ways. Thus, an extension of the process is the synthesis of highly substituted pyrrolidines, piperidines, and azepanes using aminoaldehydes. The process has also been employed for the enantioselective total synthesis of a variety of alkaloids, such as indol- and ipecacuanha alkaloids. In another domino process, erythrina and homoerythrina alkaloids have been prepared from simple phenylethylamines and ketoesters.

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