**13. Pyrimido[5,4-e[1,3,4]thiadiazolo[3,2-a]pyrimidines**

An efficient one-pot method for the synthesis of 2-methyl-5,7,9-triphenyl-8-thioxo-8,9-dihydro-5H-pyrimido[5,4-e[1,3,4]thiadiazolo[3,2-a] pyrimidin-6(7H)-one and its derivatives was reported. The present protocol is also extendable to a wide variety of substrates. The advantages of this protocol are the use of easily available catalyst, short reaction time, easy work-up, ease of product isolation, and high yield (**Figure 15**).

**Figure 15.** *Synthesis of Pyrimido[5,4-e[1,3,4]thiadiazolo[3,2-a]pyrimidines.*
