Abstract: This paper reports the reactions of o nitrobenzamides with ketones induced by titanium reagent(TiCl₄ Sm system). The results show that the low valent titanium promoted a novel reductive cyclization of o nitrobenzamides and ketones to give 1,2-dihydroquinazolin-4(3H)-ones. The products were characterized by elementary analysis, IR, ¹H NMR and X-ray single crystal diffraction. The crystal of compound 3b belongs to monoclinic system with space group P2₁/n, a =1.191 7(2)_nm, b =0.691 1(1)_nm , c =1 782 1(4)_nm, β=98.81°, V =1.455 04(5)_nm³, Z=4, D_c=1.220 g/cm³, μ =0.077 mm^-1 , F (000)=568, and final R =0.043 3 and wR =0.107 6 for reflections [ I>2σ(I) ]. In summary, a series of 1,2-dihydroquinazolin 4(3H) ones was synthesized Via reductive cyclization of o nitrobenzamides with ketones induced by the TiCl₄ Sm system. Our method possesses the advantages of easily accessible starting materials, convenient manipulation and moderate to high yield.

Key words: Low valent titanium, o-Nitrobenzamide, 1,2-Dihydroquinazolin-4(3H)-one