1,2,4-Triazolopyrimidines chemistry

Tlie chemistry of one of the four possible classes of 1,2,4-triazolopyrim-idiiies, namely l,2,4-triazolo[l,5- ]pyrimidines, was reviewed in 1993 by G. Fischer [93AHC(57)81]. In two previous chapters published in this series we reviewed the chemistry of l,2,4-triazolo[4,3- ]pyrimidines [99AHC(73)131] and their [4,3-c] congeners [99AHC(75)243]. In this chapter we survey the fourth and last class of 1,2,4-triazolopyrimidines. Tlie literature has been inspected to issue number 26, Volume 129(1998) of Chemical Abstracts. 

The chemistry of l,2,4-triazolo[4,3-a]pyrimidines is covered in the first installment of a general treatment of 1,2,4-triazolopyrimidines (isostears of purines) by Professor M. A. E. Shaban and Dr. A. E. A. Morgaan (Alexandria University, Egypt). The final installment of Dr. I. Hermecz s (CHINOIN Ltd., Hungary) five-part-series on pyrido-oxazines, -diazines, and -thiazines comprises Chapter 4 of the present volume and covers ben-zologs of pyrido[l,2,-a]pyrimidines. Parts I through IV appeared in Volumes 69-72 of our series. 

The name 8-azapurine, much used in chemistry and universally in biology, is short and self-explanatory. The full replacement name 1,2,3,4,6-pentaazaindene sometimes occurs in publications, and some editors prefer the fusion name [1//, 2H, or 3//]-l,2,3-triazolo[4,5-Chemical Abstracts. Some editors replace the 1,2,3 by v. When described as 8-azapurines (as will be done consistently on this review), the structures 2-6 (inclusive) are numbered as shown in 2. When described as triazolopyrimidines, structures 2-6 are numbered as in 7. 

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