Lewis Acid-mediated Ring Expansion Reaction of 2,3-Methanochromanones with Silyl Enol Ethers

Absl~act -In the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf), methanochromanones easily reacted with silyl enol ethers to give the [3+2] cycloadducts and the corresponding adducts in good yields.Cyclopropanes having an electron-withdrawing or -donating group are susceptible to ring-opening reactions.'Especially, cyclopropanes with donor and acceptor substituents at vicinal positions on the cyclopropane ring are the equivalent of a ring-opened 1,3-zwitterion, which is expected to react with both nucleophiles and electr~~hiles.' Saigo reported the syntheses of 5-membered carbo-' and heterocyclic compounds' by the reactions of 2,2-dialkoxycyclopropanecarboxylic acid esters having two electrondonating groups and one electron-withdrawing group with various substrates.Kuwajima also reported Lewis acid-mediated [3+2] cycloaddition reaction of vicinally donor-acceptor-substituted cyclopropane