Synthesis of exo- and endo-brevicomin and frontalin

1979 ◽  
Vol 57 (12) ◽  
pp. 1475-1480 ◽  
Author(s):  
Phaik-Eng Sum ◽  
Larry Weiler
Keyword(s):  
Lewis Acid ◽  
Stereospecific Synthesis ◽  
Methyl Acetoacetate ◽  
Natural Pheromone

The dianion of methyl acetoacetate is alkylated at the γ-carbon with homoallylic bromides. The resulting alkenes are epoxidized and then cyclized with a Lewis acid to produce esters of 6,8-dioxabicyclo[3.2.1]octane. These esters can be hydrolyzed and decarboxylated in a novel reaction. This methodology has been applied to a stereospecific synthesis of the title compounds. In addition, one of the intermediates in the exo-brevicomin synthesis can be resolved to provide the natural (+)-pheromone.

The synthesis of the isomeric components of San Jose scale pheromone — an illustration of a stereospecific synthesis of trisubstituted alkenes

1993 ◽  
Vol 71 (11) ◽  
pp. 1955-1963 ◽  
Author(s):  
Margot Alderdice ◽  
Claude Spino ◽  
Larry Weiler
Keyword(s):  
Grignard Reagent ◽  
Alkylating Agents ◽  
Coupling Reaction ◽  
Stereospecific Synthesis ◽  
San Jose ◽  
Methyl Acetoacetate ◽  
Keto Ester ◽  
San Jose Scale ◽  
Trisubstituted Alkenes ◽  
Enol Phosphate

The three isomeric components of the San Jose scale pheromone, 5–7, have been synthesized from a common β-keto ester intermediate. A study of the alkylation of the dianion of methyl acetoacetate with a series of alkylating agents with the same carbon skeleton has been carried out. The trisubstituted alkenes in 5 and 6 have been synthesized stereospecifically via a copper-catalyzed coupling of a methyl Grignard reagent with the E or Z enol phosphate from the alkylated β-keto ester. In the case of the Z enol derivative, the coupling reaction was carried out on the diethyl- and diphenylphosphates, and the enol triflate. The diethyl enol phosphate gave the highest stereoselectivity. The synthetic pheromones were attractive to San Jose scale in the field.[Formula: see text]

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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