Lewis acid-promoted reactions of ethenetricarboxylates with γ-CF3-substituted propargyl alcohols

The Lewis acid-promoted reaction of an ethenetricarboxylate derivative (1) with CF3-substituted propargyl alcohols has been examined. Reaction of γ-CF3 propargyl alcohols in the presence of zinc bromide gave five-membered CF3-containing tetrahydrofurans in 66–85% yield. The CF3 group activates alkyne as an electron-withdrawing group. On the other hand, reaction of γ-trifluoromethyl-α-aryl propargyl alcohols 2 with 1 in the presence of 1 equiv of SnCl4 gave cyclobutane derivatives 6 in 29–49% yield. Formation of cyclobutane 6a arises from the [2+2] cycloaddition between ethenetricarboxylate 1 and chloroallene 8, which is produced by the reaction of propargyl alcohol 2a and SnCl4.