Synthesis of Thiazolo[3,2-<i>a</i>]pyrimidines and Oxazolo[3,2-<i>a</i>] pyrimidinium Salts from 3-Isothiocyanato-2-propeniminium Salts and α-Aminocarbonyl Compounds
作者:Jürgen Liebscher、Ahmed Hassoun
DOI:10.1055/s-1988-27720
日期:——
The easily available 3-isothiocyanato-2-propeniminium salts 2 react with α-aminoacetophenone or ethyl glycinate to give 1-phenacyl-2-thioxo-1,2-dihydropyrimidines 4 or 1-ethoxycarbonylmethyl-2-thioxo-1,2-dihydropyrimidines 6, respectively. Compounds 4 can be directly cyclized to thiazolo[3,2-a]pyrimidinium salts 5. Compounds 6 are first submitted to alkaline hydrolysis and the resultant free acids 7 cyclized to the mesoionic thiazolo[3,2-a]pyrimidine derivatives 8 by reaction with carboxylic anhydrides. S-Methylation of compounds 4 followed by base-catalyzed elimination of methanethiol affords oxazolo[3,2-a]pyrimidinium salts 10.
容易获得的 3-异硫氰基-2-丙烯亚胺盐 2 与δ-氨基苯乙酮或甘氨酸乙酯反应,分别生成 1-苯乙酰基-2-硫酮-1,2-二氢嘧啶 4 或 1-乙氧羰基甲基-2-硫酮-1,2-二氢嘧啶 6。化合物 4 可直接环化为噻唑并[3,2-a]嘧啶盐 5。首先将化合物 6 进行碱性水解,然后将生成的游离酸 7 与羧酸酐反应,环生成介离子型噻唑并[3,2-a]嘧啶衍生物 8。化合物 4 经 S-甲基化,然后在碱催化下消除甲硫醇,得到噁唑并[3,2-a]嘧啶鎓盐 10。