presence of the N-heterocyclic carbene gold catalyst (NHC-AuIPr, 7), propargyl esters 1a–f and 13 undergo a [4C+3C] cycloaddition reaction with cyclopentadiene and furan under mild conditions. The evidence suggests that the formation of the seven-membered ring occurs by a direct cycloaddition process, rather than a stepwise cyclopropanation/Cope rearrangement sequence.
Gold(I)-Catalyzed Divergence in the Preparation of Bicyclic Enol Esters: From Exclusively [3C+2C]-Cycloaddition Reactions to Exclusive Formation of Vinylcyclopropanes
作者:Ryan C. Conyers、Benjamin W. Gung
DOI:10.1002/chem.201202881
日期:2013.1.7
Vinylcyclopropanes formed from dihydrofuran and dihydropyran resisted such rearrangement, even in the presence of fresh AuI catalyst at elevated temperature. This study addresses an important mechanistic question concerning whether the five‐membered‐ring products were produced by a direct [3C+2C] cycloaddition reaction or by a sequential cyclopropanation/ring‐expansion reaction. A dual pathway is proposed for the AuI‐catalyzed