Unexpected formation of trifluoromethylated spiro or fused cyclic compounds from 4-ethyloxy-1,1,1-trifluoro-3-buten-2-one and silyl enol ethers

Two kinds of trifluoromethylated spiro or fused cyclic compounds were synthesized via the unexpected direct alpha,alpha'-dialkylation of (E)-4-ethoxy-1,1,1-trifluoro-3-buten-2-one (1) with silyl enol ethers in the presence of boron trifluoride etherate.