Totalsynthesis of the title compounds is described. The key intermediate, dehydro-pentacyclic 13, is prepared in a sequence involving Pictet-Spengler reaction and DDQ oxidation. The key step in the synthesis was the dihydroxylation of 13 to afford the cis-diol 54, which was performed by direct oxidation with osmium tetroxide, whereas treatment of 13 with N-bromo-succinimide provided the trans-diol
L-threonine aldolase in organic synthesis: Preparation of novel β-hydroxy-α-amino acids
作者:Vassil P. Vassilev、Taketo Uchiyama、Tetsuya Kajimoto、Chi-Huey Wong
DOI:10.1016/0040-4039(95)00720-w
日期:1995.6
The L-threonine aldolasefromCandidahumicola was used in the synthesis of multifunctional β-hydroxy-α-amino acids. Of many aldehydes with different substituents tested as substrates for reaction with glycine, benzyloxy- and alkoxy-aldehydes are found to be good substrates, providing a new synthetic route to α-amino-β,ω-dihydroxy and α,ω-diamino-β-hydroxy acids. The enzymatic reactions are not stereospecific
Tandem reductive lithiations ? Carbanionic cyclizations yielding sulfur stabilized cyclopropyl- and cyclobutylcarbinyllithiums
作者:Fangping Chen、Boguslaw Mudryk、Theodore Cohen
DOI:10.1016/s0040-4020(98)01141-7
日期:1999.3
nucleophilic addition to the vinyl sulfide group, usually at −78 °C, leading to a phenylthio-stabilized cyclopropyl- or cyclobutylcarbinyllithium. The substrates were prepared by Wittig or Peterson olefination of carbonyl compounds which were in turn generated by conjugate addition of thiophenol or of the cuprate of a phenylthio-stabilized carbanion to an α,β-unsaturated carbonyl compound.
Cyclization by Intramolecular Carbolithiation of Alkyl- and Vinyllithiums Prepared by Reductive Lithiation: Surprising Stereochemistry in the Lithium Oxyanion Accelerated Cyclization
作者:Kai Deng、Ahlem Bensari、Theodore Cohen
DOI:10.1021/ja027988c
日期:2002.10.1
yield cyclopentylmethyllithiums by unconjugated organolithiums is greatly increased (1) by generating the organolithiums by reductive lithiation of phenyl thioethers with aromatic radical anions and (2) by using allylic or homoallylic alcohol groups on the receiving alkene. This type of reductive lithiation allows virtually any kind of organolithium to be generated, usually in a connective manner.
heterodimeric indole/coumarin natural product exotine B was synthesized for the first time. The carbon skeleton of the natural product was formed rapidly by a palladium-catalyzed Suzuki cross-coupling reaction and a gallium-catalyzed three-component [4 + 3] cycloaddition reaction. An alternative biosynthesis of exotine B is proposed based on the totalsynthesis. Improved syntheses of coumarin natural products