Cycloisomerization versus Hydration Reactions in Aqueous Media: A Au(III)-NHC Catalyst That Makes the Difference
作者:Eder Tomás-Mendivil、Patrick Y. Toullec、Josefina Díez、Salvador Conejero、Véronique Michelet、Victorio Cadierno
DOI:10.1021/ol300811e
日期:2012.5.18
A novel water-soluble Au(III)-NHC complex has been synthesized and successfully applied in the intramolecular cyclization of gamma-alkynoic acids into enol-lactones under biphasic toluene/water conditions, thus representing a rare example of an active and selective catalyst for this transformation In aqueous media. Remarkably, competing alkyne hydration processes were not observed, even during the desymmetrization reaction of challenging 1,6-diyne substrates. In addition, after phase separation, the water-soluble Au(III) catalyst could be recycled 10 times without loss of activity or selectivity.
Palladium-catalyzed reaction of vinyl triflates and vinyl/aryl halides with 4-alkynoic acids: regio- and stereoselective synthesis of (E)-.delta.-vinyl/aryl-.gamma.-methylene-.gamma.-butyrolactones
作者:Antonio Arcadi、Alfredo Burini、Sandro Cacchi、Monica Delmastro、Fabio Marinelli、Bianca Rosa Pietroni
DOI:10.1021/jo00029a035
日期:1992.1
The palladium-catalyzed reaction of vinyl triflates and vinyl/aryl halides with 4-pentynoic acid, 2,2-disubstituted 4-pentynoic acids, and 5-substituted 4-pentynoic acids produced regio- and stereoselectively the corresponding (E)-delta-vinyl/aryl-gamma-methylene-gamma-butyrolactones in good to high yield. Reactions were carried out in the presence of catalytic amounts of Pd(OAc)2(PPh3)2 or Pd(PPh3)4, Et3N, and n-Bu4NCl. The presence of chloride anions was found to be necessary to obtain the best results. The proposed mechanism involves an intramolecular nucleophilic attack of the carboxylate anion on the palladium-coordinated carbon-carbon triple bond and subsequent reductive elimination of Pd(0) species from the resulting sigma-vinylpalladium complex which regenerates the catalyst and releases the exocyclic enol lactone.
Enantioselective Total Synthesis of (+)-Ophiobolin A
The enantioselective total synthesis of (+)‐ophiobolin A is described. This total synthesis features the construction of the spiro CD ring of (+)‐ophiobolin A through a stereoselective intramolecular Hosomi–Sakurai cyclization reaction, the joining of the A ring to the CD ring by using a reaction reported by Utimoto, and the construction of the ophiobolin eight‐membered carbocyclic ring through ring‐closing
Enantioselective Synthesis of α-Quaternary Amino Acid Derivatives by Sequential Enzymatic Desymmetrization and Curtius Rearrangement of α,α-Disubstituted Malonate Diesters
作者:Violeta Iosub、Anton R. Haberl、Jennifer Leung、Michael Tang、Kannan Vembaiyan、Masood Parvez、Thomas G. Back
DOI:10.1021/jo902584r
日期:2010.3.5
A convenient and versatile enantioselective synthesis of biologically important α-quaternary amino acid derivatives was based on the sequential double alkylation or arylation of dimethyl malonate, followed by desymmetrization with porcine liver esterase (PLE) and Curtius rearrangement. The PLE-mediated hydrolysis of the prochiral dialkylated malonate diesters produced the corresponding chiral half-esters