**4. Furo-pyrimidines**

It was reported [32] that furo[2,3-*d*]pyrimidines **10** were prepared by condensing 1,3-diarylthiobarbituric acids (**1**) with benzoin in presence of *p*-toluene sulphonic acid. In another reaction, derivatives of furo[2,3-*d*]pyrimidines **11** were prepared by direct condensation of the corresponding 1,3-diarythiobarbituric acids, **1** with chloroacetone in presence of triethylamine (**Figure 4**).

**Figure 3.** *Isoxazolo-pyrimidines.*

**Figure 4.** *Furo-pyrimidines.*
