... Tetrahedron Letters. Volume 28, Issue 37, 1987, Pages 4275–4278. Cover image Cover image. What is the structure of barettin? Novel synthesis of unsaturated diketopiperazines. ☆. ... Full Text via CrossRef. 2; G. Lidgren, L. Bohlin; Tetrahedron Lett., 27 (1986), p. 3283. ...