Chapter 6.2 Six-membered ring systems: diazines and benzo derivatives

• Published in: Progress in Heterocyclic Chemistry Vol. 9; pp. 249 - 267
• Main Author: Groziak, Michael P.
• Format: Book Chapter
• Language: English
• Published: Elsevier B.V 1997
• ISBN: 0080428010; 9780080428017
• ISSN: 0959-6380
• DOI: 10.1016/S0959-6380(97)80015-3

This chapter provides information on six-membered ring systems, including diazines and benzo derivatives. Isolated and benzo-fused diazine rings are key structural elements in many natural and synthetic compounds of current interest. The chapter discusses the syntheses, reactions and applications of (1) pyridazines and benzoderivatives, (2) pyrimidines and benzoderivatives, and (3) pyrazines and benzoderivatives. Potentially tautomeric methyl/methylidene derivatives of pyridine and diazines were the subject of a review focusing on hydrogen isotope exchanges, alkylations, and acylations. Alkylation of various azines and diazines has afforded a set of congeners of pyridazomycin, an antimicrobial natural product. Pyrimidines and pyridazines were among the compounds obtained from cyclization reactions involving ethyl 2-amino-4,5,6,7-tetrahy drobenzo[b]thiophene- 3-carboxylate. Ortho-directed lithiation followed by reaction with TsN3 and reduction has led to an improved, general synthesis of aminodiazines 3a-c. Pyrimidines and related condensed ring systems continue to be attractive as anticancer agents. Studies of nonsymmetrical dimeric steroid-pyrazine marine alkaloids have led to the total synthesis of dihydrocephalostatin 1 and to the first biologically active cephalostatin analogs. Quinoxalines are of interest as antispasmodics, 5-HT3 receptor antagonists, inhibitors of PGF receptor tyrosine kinase, streptonigrin analogs, and antifolates.