... [2] MF Rahman, P. Neellakantan and G. Thyagarajan, Indian J. Chew... ... [5] For a recent review of these ring systems see PN Preston, in "The Chemistry of Heterocyclic Compounds", A ... Page 3. May-Jun 1987 Heterocycles. 10 563 [7] HR Matthews and H. Rapoport, /. Am. Chem. ...