Et2AlCl-promoted asymmetric phenylseleno group transfer radical cyclization reactions of unsaturated beta-hydroxy esters

J Org Chem. 2004 Dec 10;69(25):8821-8. doi: 10.1021/jo048322z.

Abstract

We have developed a new method for asymmetric phenylseleno group transfer radical cyclization of unsaturated beta-hydroxy esters. Various unsaturated alpha-phenylseleno beta-hydroxy esters underwent radical cyclization in the presence of Et(2)AlCl in benzene with sunlamp irradiation at 25-30 degrees C to give mono- and bicyclic group-transferred products in an efficient and highly regioselective and diastereoselective manner. To rationalize the high diastereoselectivities observed in this reaction, we propose a model based on chelation control of the aluminum alkoxides that are formed in situ. We devised a general method to prepare chiral radical precursors from which we obtained highly optically pure mono- and bicyclic group transfer products. The synthetic advantages of this method are demonstrated by our formal total synthesis of (-)-wilforonide. This paper presents the first examples of stereoselective group transfer radical cyclizations that occur via 1,2-asymmetric induction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aluminum Compounds / chemistry*
  • Cyclization
  • Esters / chemical synthesis*
  • Free Radicals / chemistry
  • Hydroxy Acids / chemical synthesis
  • Molecular Conformation
  • Organometallic Compounds / chemistry*
  • Selenium / chemistry

Substances

  • Aluminum Compounds
  • Esters
  • Free Radicals
  • Hydroxy Acids
  • Organometallic Compounds
  • Selenium