Crystal structures of two 6-(2-hy­droxy­benzo­yl)-5H-thia­zolo[3,2-a]pyrimidin-5-ones

The title compounds, 6-(2-hy­droxy­benz­yl)-5H-thia­zolo[3,2-a]pyrimidin-5-one, C(13)H(8)N(2)O(3)S, (1), and 6-(2-hy­droxy­benz­yl)-3-methyl-5H-thia­zolo[3,2-a]pyrimidin-5-one, C(14)H(10)N(2)O(3)S, (2), were synthesized when a chromone-3-carb­oxy­lic acid, activated with (benzotriazol-1-yl­oxy)tripyrrolidinyl­phospho­nium hexa­fluorido­phosphate (PyBOP), was reacted with a primary heteromamine. Instead of the expected amidation, the unusual title thia­zolo­pyrimidine-5-one derivatives were obtained serendipitously and a mechanism of formation is proposed. Both compounds present an intra­molecular O—H⋯O hydrogen bond, which generates an S(6) ring. The dihedral angles between the heterocyclic moiety and the 2-hydroxybenzoyl ring are 55.22 (5) and 46.83 (6)° for (1) and (2), respectively. In the crystals, the mol­ecules are linked by weak C—H⋯O hydrogen bonds and π–π stacking inter­actions.