Mannich-type reactions of aldehydes with secondary amines and a ketene silyl acetal were promoted by trimethoxyborane in DMSO to afford the corresponding β-amino esters in good yields. B(OMe)3 also promoted Ugi-typereactions ofaldehydes with secondary amines and isocyanides in 1,2-dichloroethane, which leads to the formation of α-amino amides. In these reactions, trimethoxyborane serves as an inexpensive