Intramolecular Carbolithiation of Alkynes: <i>anti</i> Selectivity

Abstract

A stereochemical twist in the tale: The treatment of the propargylic acetal 1 with one equivalent of n-butyllithium provided the dihydrobenzofuran 2 with an exocyclic E double bond. The results of DFT calculations suggest that strong coordination between the lithium cation and one oxygen atom of the acetal group drives the triple bond toward an E alkene. (A representation of the electron distribution near the transition state is shown on the right.) Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z704139_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.