Metal-Templated Macrolactamization of Triamino and Tetramino Esters. Facile Synthesis of Macrocyclic Spermidine and Spermine Alkaloids, (<i>S</i>)-(+)-Dihydroperiphylline, (±)-Buchnerine, (±)-Verbacine, (±)-Verbaskine, and (±)-Verbascenine

Abstract The total synthesis of spermidine and spermine alkaloids, (S)-(+)-dihydroperiphylline (1), (±)-buchnerine (2), (±)-verbacine (3), (±)-verbaskine (4), and (±)-verbascenine (5), is described. The construction of macrocyclic lactams has been efficiently accomplished by the metal-templated cyclization of triamino esters and tetraamino esters. It was also found that the antimony(III) ethoxide is useful as an intermolecular amidation catalyst.