As a consequence of the necessity of milder and environmentally friendly reaction conditions, and in continuation of our interest on the application of erbium triflate into organic transformations; in this Letter, we aim to report that Er(OTf) 3 can act as a mild and efficient Lewis acid catalyst for another regio- and stereoselective epoxide ring opening with trimethylsilylazide (TMSN 3 ) and trimethylsilylcyanide (TMSCN) (Scheme 1). ... Moreover, β-hydroxynitriles ...