[BH4-].[Na+].[Te].C(O)(=O)C.C(N(CC1C=CC=CC=1)C(=O)C=[C:15]1[S:27][C:18]2=[N:19][C:20]3[C:25]([CH2:26][N:17]2[C:16]1=[O:28])=[CH:24][CH:23]=[CH:22][CH:21]=3)(C)(C)C>C(O)C>[O:28]=[C:16]1[N:17]2[C:18](=[N:19][C:20]3[C:25]([CH2:26]2)=[CH:24][CH:23]=[CH:22][CH:21]=3)[S:27][CH2:15]1
A suspension of sodium borohydride (0.08 mol) and tellurium powder (0.034 mol) in 135 ml of anhydrous ethanol is heated under nitrogen atmosphere, preferably for about 15 min. After cooling to -20° C., 8.08 ml glacial acetic acid in 33.65 ml anhydrous ethanol solution (8.08:33.65 v/v) is added dropwise, and the mixture is stirred at -20° C. for 5 min. Stirring is followed by the addition of 0.013 mol of a substituted 2,3-dihydro-5H-thiazol[2,3-b]quinazoline derivative, synthesized by the procedures in the preceding sections (2) to (5), and dissolved in 13.5 ml anhydrous ethanol. The reaction mixture is allowed to warm up to ambient temperature and stirred for about 10 hours. The mixture is filtered through celite, and evaporated under reduced pressure. The residue is taken up in water and extracted with chloroform. The organic extract is dried over anhydrous magnesium sulfate and evaporated under reduced pressure, yielding the corresponding 2,3-dihydro-3-oxo-5H-thiazolo[2,3-b]quinazoline derivative with a saturated exocyclic bond at the 2 position of the 2,3-dihydro-5-thiazo[2,3-b]quinazoline moiety.
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