Synthesis of (±)-karahana ether and a (±)-labdadienoic acid by the electrophilic cyclization of epoxy allylsilanes

1986 ◽  
Vol 64 (3) ◽  
pp. 584-596 ◽  
Author(s):  
Rosemary J. Armstrong ◽  
Larry Weiler
Keyword(s):  
Good Yield ◽  
Lewis Acids ◽  
Electrophilic Cyclization ◽  
Keto Esters

The epoxy allysilanes 7 and 16 were synthesized by stereoselective routes from β-keto esters and cyclized with Lewis acids in good yield. The monocyclic product from 7 was converted into (±)-karahana ether (10), and the bicyclic product from 20 was used in a synthesis of the 3-hydroxylabdadienoic acid 24b.[Formula: see text]

scholarly journals Palladium-catalyzed alkylation of unactivated olefins

2004 ◽  
Vol 76 (3) ◽  
pp. 671-678 ◽  
Author(s):  
Ross A. Widenhoefer
Keyword(s):  
Good Yield ◽  
Catalytic Amount ◽  
Outer Sphere ◽  
Deuterium Labeling ◽  
Carbon Nucleophiles ◽  
Keto Esters ◽  
Reactive Carbon ◽  
Aryl Ketones ◽  
Palladium Catalyzed ◽  
Hydride Elimination

The reaction of a 3-butenyl β-diketone with a catalytic amount of PdCl2(CH3CN)2 in dioxane at room temperature led to olefin hydroalkylation and formation of the corresponding 2-acylcyclohexanone in good yield as a single regioisomer. Deuterium-labeling experiments for the hydroalkylation of 7-octene-2,4-dione were in accord with a mechanism involving outer-sphere attack of the pendant enol on a palladium-complexed olefin to form a palladium cyclohexyl species, followed by palladium migration via iterative β-hydride elimination/addition and protonolysis from a palladium enolate complex. In comparison to a 3-butenyl β-diketone, reaction of a 4-pentenyl β-diketone with a catalytic amount of PdCl2(CH3CN)2 in the presence of CuCl2 led to oxidative alkylation and formation of the corresponding 2-acyl-3-methyl-2-cyclohexenone in good yield as a single isomer. Unactivated olefins tethered to less reactive carbon nucleophiles such as β-keto esters, α-aryl ketones, and even dialkyl ketones underwent palladium-catalyzed hydroalkylation in the presence of Me3SiCl or HCl to form the corresponding cyclohexanones in moderate-to-good yield with high regioselectivity.

Gold-catalyzed generation of vinylthionium ions and the development of an organocatalytic, asymmetric (4+3)-cycloaddition reaction

2017 ◽  
Author(s):  
◽  
Michael Topinka
Keyword(s):  
Amino Alcohol ◽  
Good Yield ◽  
Lewis Acids ◽  
Cycloaddition Reaction ◽  
Unsaturated Ester ◽  
Cycloaddition Reactions ◽  
University Of Missouri ◽  
Considerable Problem ◽  
The University ◽  
Substituted Furans

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] An allylic benzoate ester was prepared and used as a progenitor of vinylthionium ions for (4+3)-cycloaddition reactions. The chemistry was limited to 2-substituted and 2,5-disubstituted furans. In the case of 2-substituted furans, only Friedel-Crafts alkylation products were procured. In the case of 2,5-disubstituted furans, (4+3)-cycloaddition products were furnished in good yield. A catalytic, asymmetric variant using 2,5-dialkylfurans and chiral acids to procure cycloaddition products was unsuccessful. There was an opportunity to overcome the Friedel-Crafts alkylation problem that arose in a gold-catalyzed cycloaddition project. A sulfur-substituted unsaturated ester and alcohol were prepared, but silyl migration was a considerable problem upon activation by various agents. The problem of silyl migration was circumvented, but the target aldehyde was unreactive toward dienes in the presence of various Lewis acids. In further pursuit of an asymmetric (4+3)-cycloaddition reaction, 2-substituted furans were reacted with 2-tosyloxycyclopentanone in the presence of K2HPO4/H2O in perfluorobenzene as solvent and 30 mol% of an amino alcohol catalyst developed by David MacMillan. Enantioselectivities were modest for 2-alkylfurans and excellent for 2-arylchalcogenofurans (90% ee). 3-Substituted furans also work in this process.

Synthesis of (±)-albicanyl acetate and (±)-isodrimenin by the electrophilic cyclization of olefinic allylsilanes

1986 ◽  
Vol 64 (5) ◽  
pp. 1002-1006 ◽  
Author(s):  
Rosemary J. Armstrong ◽  
Francis L. Harris ◽  
Larry Weiler
Keyword(s):  
Lewis Acids ◽  
Electrophilic Cyclization

The allylsilane 3 was synthesized and cyclized with Lewis acids or mercuric trifluoroacetate to give 5 or 6, which were converted into albicanyl acetate (7) and isodrimenin (12).[Formula: see text]

The Retro-Michael Reaction of 1,5-Dicarbonyl Compounds: Scope and Limitation

1999 ◽  
Vol 64 (1) ◽  
pp. 107-113 ◽  
Author(s):  
Jian-Xin Wang ◽  
Tong-Shuang Li
Keyword(s):  
Good Yield ◽  
Steam Distillation ◽  
Michael Reaction ◽  
Glass Wool ◽  
Dicarbonyl Compounds ◽  
Keto Esters ◽  
Tricyclic Compounds ◽  
Keto Acids

Under catalysis of NaOH or KOH adsorbed on glass wool and by using steam distillation, (20R,S)-4,4,5,14-tetramethyl-18,19-dinor-13,17-seco-5β,8α,9β,10α,14β-cholestane-13,17-dione (1) and 3,14-dioxo-14,15-seco-5α-cholestan-15-al (4) gave good yield (>59%) of the corresponding tricyclic compounds (8a, 8b and 10a) via a retro-Michael reaction at 250 °C. While 5-oxo-4-nor-3,5-secocholestan-3-oic acid (6) and ethyl 5-oxo-4-nor-3,5-secocholestan-3-oate (7) afforded low yield (<15%) of the retro-Michael cleavage products (12a, 12b) at the same conditions. Thus, the retro-Michael reaction worked well for 1,5-diketones and 1,5-keto aldehydes but gave poor yield for 1,5-keto esters and 1,5-keto acids.

scholarly journals Electrophilic Cyclization of Diterpenoids

2006 ◽  
Vol 1 (1) ◽  
pp. 22-35
Author(s):  
Veaceslav Kulciţki ◽  
Marina Grinco ◽  
Pavel Vlad ◽  
Nicon Ungur
Keyword(s):  
Lewis Acids ◽  
Electrophilic Cyclization ◽  
Cyclization Reactions ◽  
Practical Utility ◽  
Electrophilic Reagents

A review of diterpenoid cyclization initiated by electrophilic reagents is provided. Conventional protonic and Lewis acids are examined along with superacids as initiators of cyclization cascade. An emphasis is placed on the use of cyclization reactions as a tool for the synthesis of compounds with potential practical utility. The review contains 74 references.

Synthesis of 5-tert-butyl-8,12,14-trimethyl- and 5-tert-butyl-8,12,14,16-tetramethyl[2.2]metacyclophane and their treatment with Lewis acids in benzene

2009 ◽  
Vol 2009 (7) ◽  
pp. 443-447 ◽  
Author(s):  
Tomoe Shimizu ◽  
Katsuhiko Hida ◽  
Takehiko Yamato
Keyword(s):  
Good Yield ◽  
Lewis Acids ◽  
The Other ◽  
Tert Butyl ◽  
Other Hand

Treatment of 5- tert-butyl-8,12,14,16-tetramethyl[2.2]MCP with AlCl3-MeNO2 in benzene led to trans- tert-butylation to afford 8,12,14,16-tetramethyl[2.2]MCP in good yield along with tert-butylbenzene. On the other hand, the same treatment of 5- tert-butyl-8,12,14-trimethyl[2.2]MCP led to transannular cyclisation reaction and isomerisation reaction to afford the corresponding strainless 2- tert-butyl-3a,6,8-trimethyl-3,3a,4,5,9,10-hexahydropyrene in good yield.

Synthesis of (±)-trixagol by an electrophilic cyclization of an allylsilane

1983 ◽  
Vol 61 (11) ◽  
pp. 2530-2539 ◽  
Author(s):  
Rosemary J. Armstrong ◽  
Larry Weiler
Keyword(s):  
Lewis Acids ◽  
Electrophilic Cyclization ◽  
Trimethylsilyl Group ◽  
Monocyclic Compound

1,5-Dienes containing an allylsilane are cyclized by Lewis acids to methylenecyclohexanes. The trimethylsilyl group exerts a strong activating and directing influence on the regioselectivity of this cyclization. The monocyclic compound 10 was converted into the diterpene, (±)-trixagol (3).[Formula: see text]

Electrophilic cyclization of polyene allylsilanes. Synthesis of albicanyl acetate

1982 ◽  
Vol 60 (5) ◽  
pp. 673-675 ◽  
Author(s):  
Rosemary J. Armstrong ◽  
Francis L. Harris ◽  
Larry Weiler
Keyword(s):  
Natural Product ◽  
Marine Natural Product ◽  
Stannic Chloride ◽  
Electrophilic Cyclization ◽  
Keto Esters ◽  
Enol Phosphate

The allylsilanes 5 [Formula: see text] were prepared by a nickel(II) catalyzed coupling of trimethylsilylmethylmagnesium chloride with the enol phosphate of the corresponding β-keto esters. Stannic chloride and mercuric trifluoroacetate effected a cyclization of 5. The product from 5b was converted into the marine natural product, albicanyl acetate (1)[Formula: see text]

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