A new synthesis of the 2,2,3,5,6,6-substituted tetrahydropyran aplysiapyranoid A and its 5-epimer
摘要:
The vanadium(V)-catalyzed oxidation of bromide in the presence of methyl (E)-2-(1-hydroxy-1-methylethyl)-5-phenyl-4-hexenoate furnished 5,6-trans-5-bromo-6-phenyl-2,2,6-trimethyl-3-methytoxycarbonyltetrahydropyran, which was converted into the marine natural product aplysiapyranoic A and its 5-epimer, via a short sequence of decarboxylative bromination and transition metal-based procedures for transforming a phenyl into a chlorovinyl Substituent. (C) 2003 Elsevier Ltd. All rights reserved.
Masked β-, γ- and δ-lithium ester enolates: useful reagents in organic synthesis
作者:Isidro M Pastor、Miguel Yus
DOI:10.1016/s0040-4039(00)02172-9
日期:2001.2
acid-catalysed methanolysis, to functionalised methyl esters 2. In the case of chlorotrimethylsilane, hydroxyethyl esters 2′ are isolated. The reaction is also applied to bicyclic orthoesters 3: whereas β-chloro derivatives and carbonyl compounds gives directly γ-lactones 4 after hydrolysis, the corresponding γ-chloro derivative affords the expected methyl esters after methanolysis.
The protocol of lithiation by means of lithium and a catalytic (5% molar) amount of DTBB (4,4’-di-tert-butylbiphenyl), applied to ω-chloro ortho ester 6 under Barbier-type conditions gives, after final acid-catalyzed methanolysis, the corresponding functionalized esters 8 or 9 (for chlorotrimethylsilane as electrophile) or, after ortho ester deprotection and acid catalyzed treatment, the δ-lactones 11. The procedure is also practical for bicyclic ortho esters 14: the β-chloro OBO ester derivate generates the γ- lactones 15 and the γ-chloro OBO ester gives corresponding esters 8.