A Convenient Method for the Synthesis of 4,4‐Diarylbut‐1‐enes via the Successive Allylation of Aromatic Aldehydes and the Friedel—Crafts Alkylation Reaction of Aromatic Nucleophiles with the Intermediary Benzyl Silyl Ethers Using HfCl4 or Cl2Si(OTf)2. |