多聚磷酸存在下取代6-苄硫基嘧啶与羧酸的环合反应研究

Studies on Cyclization Reactions of 6-Benzylthiopyrimidine-4,5-diamines and Carboxylic Acids in Presence of Polyphosphoric Acid

以多聚磷酸（PPA）为催化剂，对取代6-苄硫基嘧啶与羧酸的反应进行了研究．当羧酸为脂肪酸时，在60～80℃下反应，可选择性地得到6-苄硫基嘌呤衍生物；改用芳香酸时，则得到硫上的苄基被脱除的6-巯基嘌呤和嘧啶并[5，4-d]噻唑；如果将嘧啶4-位上伯胺取代基变成仲胺取代基，只得到嘧啶并[5，4-d]噻唑．通过双途径反应机理对上述现象进行了解释．

The reactions of 6-benzylthiopyrimidine-4,5-diamines and carboxylic acids in presence of polyphosphoric acid were investigated. Three products, 6-benzylthiopurines 2, 6-mercaptopurines 3 and 7-aminothiazolo [ 5,4-d] pyrimidines 4 might be obtained selectively depending on the reaction conditions. When an aliphatic acid was employed, 6-benzylthiopurine 2 could be obtained by using toluene as the solvent at 60-80 ℃. An aromatic acid might yield the debenzylated product 6-mercaptopurine 3 and thiazolo[ 5,4-d] pyrimidine 4 at an elevated temperature （refluxing toluene or xylene）. Increasing in the molar ratio of polyphosphoric acid to starting 6-benzylthiopyrimidine-4,5-diamine 1 could promote the formation of 6-mercaptopurine 3. Thiazolo [5,4-d] pyrimidine 4 could be prepared as the product of choice if both hydrogen atoms of the 4-amino group in compound 1 were blocked by an aryl or alkyl. These results could be rationalized by a mechanism involving 5-acylatedaminopyrimidine 7 as the key intermediate. Compound 7 may undergo either an intramolecular reaction followed by loss of water to yield 6-benzylthiopurine 2 which may in turn be debenzylated to 6-mercaptopurine 3, or loss of benzyl to 6-mercapto intermediate 8 leading to 7-aminothiazolo [ 5,4-d ] pyrimidine 4 due to the superior nucleophilicity of 6-sulfur group to 4-amino one.