Construction of Highly-Functionalized Cyclopentanes from Silyl Enol Ethers and Activated Cyclopropanes by [3+2] Cycloaddition Catalyzed by Triflic Imide

[3+2] Cycloadditions of silyl enol ethers with donor-acceptor (D-A) cyclopropanes, such as 2-alkoxycyclopropanecarboxylates and 2-(p-methoxyphenyl)cyclopropyl phenyl ketone, proceed in the presence of a catalytic amount of triflic imide (Tf2NH) to give functionalized cyclopentanes in high yield. The catalytic process allows promotion of the cycloaddition of substrates incorporating Lewis basic functions, such as ether and carbamate moieties. Moreover, multicomponent [4+2]-[3+2] cascade cycloadditions of α,β-unsaturated carbonyl compounds, 2-siloxydienes and D-A cyclopropanes to form highly-functionalized bicyclo[4.3.0]nonanes have been demonstrated.