Selective Synthesis of 3-Methylene-2,3-dihydrofurans or 1,2,4-Trisubstituted Furans via Tandem Reactions of Allenic Ketones with α-Chloro β-Keto Esters or Ketones

Novel and efficient synthesis of functionalized furan derivatives have been developed in this paper. Promoted by K2CO3, allenic ketones underwent tandem reactions with 2-chloroacetoacetate or 3-chloropentane-2,4-dione to afford 3-methylene-2,3-dihydrofurans with high efficiency under remarkably mild conditions. When the same substrates were treated with potassium carbonate and triphenylphosphine, on the other hand, 1,2,4-trisubstituted furans could be obtained in good yields.