Expeditious Routes to Polycyclic Molecular Frameworks via One-Pot, Two-Step Ugi Ring-Closing Sequences

A very general and robust multicomponent-reaction protocol involving an Ugi condensation between ethyl glyoxylate, isonitriles, N -Boc-α-amino acids, and mono - N -Boc-protected diamines followed by a series of acid-promoted cyclization steps in a one-pot fashion is reported. This process allows for the assembly of complex polycyclic structures by means of just two simple synthetic operations and a single chromatographic purification in high overall yields. Of note, the first scaffolds derived from a highly ­selective sequence of ring-closing events involving three internal amino nucleophiles is reported.