Reaction of N, N'-di (p-toluenesulfonyl)-1, 2-diamine, 1-bromo-1-alkyne, K3PO4, and a catalytic amount of CuI in hot DMF afforded N, N'-di (p-toluenesulfonyl)-1, 2, 3, 4- tetrahydropyrazines in good yields. The reaction most likely involves (i) monoalkynylation of the diamine derivative with 1-bromo-1-alkyne, and (ii) 6-endo-dig ring closure between the acetylenic bond and another sulfonylamine moiety of the diamine. When the starting 1, 2- ...