A dipolar cycloaddition approach toward the kopsifoline alkaloid framework
摘要:
Using a metal-catalyzed domino reaction as the key step, the heterocyclic skeleton of the kopsifoline alkaloid family was constructed by a 1,3-dipolar cycloaddition of a carbonyl ylide dipole derived from a Rh(II)-catalyzed reaction of a diazo ketoester across the indole pi-bond. Ring opening of the resulting 1,3-dipolar cycloadduct followed by a reductive dehydroxylation step resulted in the formation of a critical silyl enol ether necessary for the final F-ring closure of the kopsifoline skeleton. (C) 2007 Elsevier Ltd. All rights reserved.
Application of the Rh(II) Cyclization/Cycloaddition Cascade for the Total Synthesis of (±)-Aspidophytine
摘要:
A new strategy for the synthesis of (+/-)-aspidophytine has been developed and is based on a Rh(II)-catalyzed cyclization/dipolar cycloaddition sequence. The resulting [3+2]-cycloadduct undergoes an efficient Lewis acid mediated cascade that rapidly provides the complete skeleton of aspidophytine. The synthesis also features a mild decarbomethoxylation reaction.
Total Synthesis of the Alkaloid (±)-Aspidophytine Based on Carbonyl Ylide Cycloaddition Chemistry
作者:José M. Mejía-Oneto、Albert Padwa
DOI:10.1002/hlca.200890034
日期:2008.2
The RhII-catalyzed cycloaddition cascade of an indolyl-substituted α-diazo imide was used for the totalsynthesis of the complex pentacyclic alkaloid (±)-aspidophytine. Treatment of the resulting dipolar cycloadduct with BF3⋅OEt2 induces a domino fragmentation cascade. The reaction proceeds by an initial cleavage of the oxabicyclic ring and formation of a transient N-acyl iminium ion which reacts further
Cycloaddition Protocol for the Assembly of the Hexacyclic Framework Associated with the Kopsifoline Alkaloids
作者:Xuechuan Hong、Stefan France、José M. Mejía-Oneto、Albert Padwa
DOI:10.1021/ol062029z
日期:2006.10.1
An approach to the hexacyclic framework of the kopsifoline alkaloids has been developed and is based on a Rh(II)-catalyzed cyclization-cycloaddition cascade. The resulting [3+2]-cycloadduct was readily converted into the TBS enol ether 23. Oxidation of the primary alcohol present in 23 followed by reaction with CsF afforded compound 24 that contains the complete hexacyclic skeleton of the kopsifolines.