In this account, recent accomplishments in the field of target-oriented synthesis involving allenes are summarized. Allenic α-amino acid derivatives 9, which are of interest as possible vitamin B 6 decarboxylase inhibitors, were prepared by 1,6-addition of the cyano-Gilman reagent t-Bu 2 CuLi-LiCN to 2-amino-substituted enynoates 8. and selective deprotection at either the amino or the ester group
Efficient Synthesis of 2-Hydroxy-3,4-dienoates by Oxidation of Zirconiumallenyl Enolates with Dimethyldioxirane
作者:Norbert Krause、Anja Hoffmann-Röder
DOI:10.1055/s-2006-942409
日期:2006.7
The α-hydroxylation of zirconiumallenyl enolates, obtained from β-allenic esters by deprotonation with LDA or LiN(SiMe3)2 and transmetalation with Cp2ZrCl2, with dimethyldioxirane (DMDO) selectively affords 2-hydroxy-3,4-dienoates. The oxidation proceeds usually with high yield and substrate conversion and tolerates even sensitive or unreactive substrates.
Ruthenium-Catalyzed Flash Oxidation of Allenes to α,α'-Dihydroxyketones
作者:Michael Laux、Norbert Krause
DOI:10.1055/s-1997-5759
日期:1997.7
The ruthenium-catalyzed flash oxidation of β-allenic esters 1 furnishes α,α'-dihydroxyketones 2 in 24-72% yield. In the case of the chiral allene 1e, the oxidation proceeds with good diastereoselectivity (88% de), i.e. with efficient axis to center chirality transfer. The flash oxidation can also be used for the synthesis of corticosteroids, as exemplified by the transformation of allenic steroid 4 into dihydroxyketone 5.
4-dienoates 3 were formed by treatment with LDA and Cp2TiCl2 and oxidized with dimethyl dioxirane to furnish the allenic hydroxyesters 4 with up to 90% diastereoselectivity. Smooth cyclization to the functionalized 2,5-dihydrofurans 5 was accomplished with complete axis to center chirality transfer by treatment with HCl gas in chloroform.
Elucidation of the Mechanism of the 1,6-Cuprate Addition to Acceptor-Substituted Enynes through13C Kinetic Isotope Effects: Experimental and Theoretical Studies