A Convenient Synthetic Route to Functionalized 5-Trifluoroacetyl-6-trifluoromethyl-3,4-dihydro-2H-pyrans: Hetero-Diels-Alder Reaction of β,β-Bis(trifluoroacetyl)vinyl Ethers with Electron-Rich Alkenes - Hojo, Masaru; Masuda, Ryōichi; Okada, Etsuji (Synthesis, 1990)