short and concise formal synthesis of enantiopure dihydroartemisinic acid from (R)-citronellal is described in this article. Intramolecular version of asymmetric Stetter reaction using Rovis aminoindane based NHC catalyst was explored to access the core substituted cyclohexanone framework which on functional group manipulation and late stage ring closing metathesis (RCM) reaction afforded an advanced intermediate
A novel extension of the Stork–Jung vinylsilane Robinson annelation procedure for the introduction of the cyclohexene of guanacastepene
作者:Barry B Snider、Bo Shi
DOI:10.1016/s0040-4039(01)02026-3
日期:2001.12
has been developed in a model system to introduce the cyclohexenering of guanacastepene. Cyclohexenone 16 is prepared by sequential methylation and alkylation with allylic iodide 15. One-pot epoxidation, protodesilylation and hydrolysis of the THP forms dione 19, which cyclizes with NaOMe to 24 in 57% overall yield. Reduction, Mitsunobu inversion, and selective oxidation of the primary alcohol forms
Annelation reactions related to the Robinson reaction are reviewed with an emphasis being placed on the regiochemistry and stereochemistry obtained in the annelation sequence. Annelations employing ring formation by a "3′-oxobutyl" side chain, or its functional equivalent are covered, and examples of experimental procedures have been selected to provide guidelines for application of a given sequence to other molecules. 1. Introduction 2. The Robinson Annelation 3. Regiochemistry of Addition to Unsymmetrical Ketones 3.1. Annelations with Enamines 3.2. Annelations using Activating or Directing Groups 3.3. Annelations using Blocking Groups 4. Stereochemistry 5. Annelations using Stabilized Electrophiles as Michael Acceptors 6. Annelations using Electrophiles with Masked Carbonyl Functions 6.1. The Wichterle Reaction 6.2. The Isoxazole Annelation 7. Annelations Involving Oxidation of Alkenyl Side Chains 8. Bis-Annelations
Several artemisinin derivatives carrying several groups (alkyl, hydroxyalkyl, allyl or azide) at position 9 have been synthesized starting from artemisinin via enolate formation and subsequent reaction with appropriate electrophiles.