Synthesis of Benzodiazepine β-Turn Mimetics by an Ugi 4CC/Staudinger/Aza-Wittig Sequence. Solving the Conformational Behavior of the Ugi 4CC Adducts

5-Oxobenzo[e][1,4]diazepine-3-carboxamides were synthesized by sequential Ugi reaction-Staudinger/aza-Wittig cyclization. The pseudopeptidic backbone of the new benzodiazepine derivatives superimposed well with type I, I', II, and II' beta-turn motifs. The intermediate Ugi adducts were characterized as two conformers of the enol form by the correlation between (1)H NMR spectra and X-ray diffraction structures of model compounds.