The aza-Diels–Alder reaction of trans-1-methoxy-2-methyl-3-trimethylsiloxybuta-1,3-diene with N-benzhydryl imines in the presence of Yb(OTf)3 in toluene at room temperature gave the corresponding 2,5-disubstituted 2,3-dihydro-4-pyridones in high yields. This reaction can also be carried out with diene, aldehydes, and amine in a three-component one-pot reaction manner in moderate to high yields under solvent-free conditions. The relationship between Lewis acids and activity, solvents and catalyst loading were studied. Some investigation towards the reaction mechanism was discussed.

An efficient enantioselective approach to 2,5-disubstituted dihydropyrones was developed. Some easily accessible inexpensivediol ligand metal complexes were employed, and [(R)-BINOL]2–Ti(OiPr)4 complex was found to be the most effective catalyst (up to 99%yield and 99% ee in the presence of 5 mol% catalyst) for the hetero-Diels–Alder reaction between trans-1-methoxy-2-methyl-3-trimethylsiloxybuta-1,3-diene (1) and aldehydes. The potential and generality of this catalyst were evaluated by a variety of aldehydesincluding aromatic, heteroaromatic, a,b-unsaturated and aliphatic aldehydes. Based on the isolated intermediate from the reaction ofbenzaldehyde being confirmed by 1H, 13C NMR and HRMS data, the mechanism was proposed as a Mukaiyama aldol pathway.

An efficient enantioselective approach to chiral dihydropyrones has been developed by the hetero-Diels-Alder (HDA) reactions of (E)-4-methoxy-2-trimethylsiloxy-penta-1,3-diene (diene 1) withaldehydes and pyruvates. It has been found that the readily accessible (R)-BINOL-Ti(OiPr)4(1.1:1) complex was a very effective catalyst for this reaction. Aromatic, heteroaromatic, conjugated,and aliphatic aldehydes afforded the corresponding products in moderate to high isolated yields(up to 99%) with excellent enantioselectivities (up to 99% ee). The first example of highlyenantioselective synthesis of 2,2,6-trisubstituted dihydropyrones by the catalytic reaction of diene1 with pyruvates was reported. The isolated intermediates indicated that this asymmetric HDAreaction proceeded in a Mukaiyama aldol pathway. On the basis of the absolute configurations ofthe products, a possible mechanism was proposed. Moreover, the catalytic system could be used tosynthesize a series of enantioenriched

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