Triazolopteridines. II. Simple s-Triazolo[3,4-h]pteridines and some [5,1-h] and [4,3-a] isomers

Abstract

Pteridin-7-ylhydrazine (lb) reacted with appropriate ortho esters to give s-triazolo[3,4-hlpteridine (2a) and its 9-methyl derivative (2b). The same hydrazine with carbon disulfide in pyridine gave the 9-thione (2c) and thence the methylthio (2d) and dimethylaminoethylthio derivative (2e). The parent heterocycle (2a) did not undergo Dimroth rearrangement to its [1,5-h] isomer (3) but the latter was made from pteridin-7-ylamine (1c) via its dimethylaminomethyleneamino (1d) and hydroxy- aminomethyleneamino (1e) derivatives. Pteridin-2-ylhydrazine (1f) and triethyl orthoformate gave a single product shown by ¹H and ¹³C n.m.r. data to be s-triazolo[4,3-a]pteridine (4a) rather than its [3,4-b] (5), [1,5-a] or [5,1-b] isomer. The 9-methyl (4b) and 9-ethyl (4c) derivatives were made similarly.