A Mild and Efficient Synthesis of 2,5-Disubstituted 2,3-Dihydro-4pyridones Catalyzed by Yb(OTf)3

A highly efficient aza-Diels-Alder reaction of trans-1-methoxy-2-methyl-3trimethylsiloxybuta-1,3-diene with N-benzhydryl imines was catalyzed by Yb(OTf)3 in toluene at room temperature to give corresponding 2,5disubstituted 2,3-dihydro-4-pyridones in high yields. Three-component reactions of diene with aldehydes and amines were also performed smoothly to afford the desired cycloadducts under solvent-free condition in 51-86% yields.