A Simple, One-Pot Synthesis of 2,3-Dihydro-4H-pyran-4-ones via the Acid-Catalysed [4 + 2]-Cycloaddition of 1-Alkoxy-3-trimethylsilyloxy-1,3-butadienes with Aldehydes - Aben, René W; Scheeren, Hans W (Synthesis, 1982)