'Atypical Ugi' tetrazoles.

Amino acid-derived isocyano amides together with TMSN3, oxocomponents and 1° or 2° amines are common substrates in the Ugi tetrazole reaction. We surprisingly found that combining these substrates gives two different constitutional isomeric Ugi products A and B. A is the expected classical Ugi product whereas B is an isomeric product ('atypical Ugi') of the same molecular weight with the tetrazole heterocycle migrated to a different position.