Preparation of 2-amino-5-methyl-7H-1,3,4-thiadiazolo[3,2-α]pyrimidin-7-ones

Abstract

2‐Amino substituted 7H‐1,3,4‐thiadiazolo[3,2‐α]pyrimidin‐7‐ones 11a‐e were prepared by the reaction of 2‐bromo‐5‐amino‐1,3,4‐thiadiazole (1b) and diketene (8), subsequent cyclocondensation (9b → 3b) and displacement of the bromo substituents by the reaction with primary or secondary amines (3b → 11a‐e). The hydrogen atom 6‐H in the heterobicycle 3b is replaced by a Cl or Br atom in the transformation of 3b → 14a,b. The 2‐bromo‐6‐chloro compound 14a reacts chemoselectively in the 2‐position with dimethylamine (14a → 15). The structure elucidations are based on one‐ and two‐dimensional NMR techniques including a heteronuclear NOE measurement.

Synthesis and conversion of 6‐fluoro derivatives of 1,3,4‐thiadiazolo‐[3,2‐a]pyrimidine

“…Patents on 2‐trifluoromethyl derivatives [ 15] and 7‐fluorosubstituted 1,3,4‐thiadiazolo[3,2‐ a ]pyrimidines [ 16] are available. Also a few articles on the synthesis of 6‐chloro‐, 6‐bromo‐, and 6‐nitro‐1,3,4‐thiadiazolo[3,2‐ a ]pyrimidines [ 16–22] have been published. However, there is no information available on the synthesis of the derivatives of this class with a fluoro group in the position 6.…”

Computational Study of the Acid Dissociation of Esters and Lactones. A Case Study of Diketene

“…The reactivity of diketene is of interest because of its wide applications in organic synthesis, [23][24][25][26][27][28][29][30][31][32][33] where its common use as an acetoacetylating agent has somewhat been superseded, 19,34 and the fact that it is not active as a carcinogen, [35][36][37][38][39][40][41][42][43] even though analogue β-lactones such as β-propiolactone and β-butyrolactone are powerful carcinogens. 44,45 While the structure of diketene was still being discussed, the acidity of its R-hydrogen was considered.…”

“…The reactivity of diketene is of interest because of its wide applications in organic synthesis, − where its common use as an acetoacetylating agent has somewhat been superseded, , and the fact that it is not active as a carcinogen, − even though analogue β-lactones such as β-propiolactone and β-butyrolactone are powerful carcinogens. , …”