The organocatalyzed U-3CR of 4-oxoazetidine-2-carbaldehydes has been studied. In addition, the organocatalyzed P-3CR of 4-oxoazetidine-2-carbaldehydes and azetidine-2,3-diones has been described for the first time. U-3CR and P-3CR adducts have been obtained in good yields and reasonable diastereoselectivities. Phenyl phosphinic acid has been the catalyst of choice to study the scope of both organocatalyzed multicomponent reactions using a variety of β-lactams, isocyanides, and amines. Highly functionalized U-3CR and P-3CR adducts derived from β-lactams have proved to be useful substrates for the preparation of enantiopure γ-lactams and γ-lactones via N1-C2 β-lactam ring opening/cyclization under acidic or basic conditions.