Transannular vs intramolecular insertion reactions of transition metal carbenes: Evaluation of a transannular approach to cyclooctane ring synthesis

摘要

The efficacy of closing cyclooctane rings via transannular metal-stabilized carbene insertion reactions within an 11-membered macrocyclic lactone: ring was explored. The impact of performing these reactions in a transannular fashion was evaluated via a comparative study of closely analogous intramolecular (but not transannular) processes. Closure of a gamma -lactone ring via intramolecular cyclopropanation on a moderately electron-deficient nt alkene proceeded in good yield under Cu(acac)(2) catalysis, whereas analogous transannular cyclopropanation was thwarted by competitive beta -hydride migration. In contrast, use of a more electron-rich methoxy-substituted alkene resulted in successful transannular cyclopropanation to afford the desired cyclooctane ring-containing product. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 68]