Uncatalyzed, Solvent-Free [2+2] Cycloaddition of Cyclic Ketene Trimethylsilyl Acetals with Electrophilic Acetylenes

Cyclic ketene trimethylsilyl acetals reacted with electrophilic acetylenes (ethyl propynoate, dimethyl acetylenedicarboxylate and ethynyl methyl ketone) to afford the corresponding [2+2] cycloadducts. The reactions were run at room temperature, without a catalyst and under solvent-free conditions. α-Alkylidenelactones, β-oxocyclobutanecarboxylates and substituted furan derivatives proved to be readily available from the [2+2] cycloadducts by treatment either with TBAF in THF solution or with BF3·Et2O.