The Claisen rearrangement of propargyl vinyl ethers provides a new general method for the synthesis of allenic aldehydes. Boron trichloridecatalysed rearrangement of phenyl propargyl ethers gave only starting material and fission products. Cope rearrangement of a propargylvinylmalonic ester gave moderate yields of the allenic malonic ester together with fission products. The mechanistic implications of these reactions are discussed.
