Abstract
An alkylation of 3-amino-4-ethoxycarbonylpyrazole (1) under various conditions was investigated. Alkylated pyrazoles (2, 3a, b) were condensed with isocyanates or isothiocyanate to yield pyrazolylurea derivatives (4a-f, 10). Ring closure of these intermediates was carried out in a solution of sodium ethoxide and the resulting 2, 5 (or 1, 5)-disubstituted pyrazolo [3, 4-d] pyrimidines (5a-f, 11a, b) were alkylated to give 2, 5, 7 (or 1, 5, 7)-trisubstituted pyrazolo [3, 4-d] pyrimidines (6a-e, 12a, b) or 2, 5-disubstituted 6-methylmercaptopyrazolo [3, 4-d] pyrimidines (7a, b). Instead of the use of isocyanates, another methods by fusing ureas with methylpyrazole were also investigated. Furthermore, debenzylation of 2-benzylpyrazolo [3, 4-d] pyrimidines (6c, d) was carried out with 35 atm of hydrogen in an autoclave at 220°over palladium on carbon to give debenzylated compounds (13a, b).
