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

Abstract [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 (Tf 2 NH) 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.