Synthesis of 5,6-dimethoxyquinazolin-2(1 H )-ones

Synthesis of 5,6-dimethoxyquinazolin-2(1H)-one derivatives was the subject of investigations leading to the preparation of title compounds 11, 13, 14 and 26. Target quinazolines 1 were synthesized in three ways; the route starting from o-vanillin via the intermediacy of 6-amino-2,3-dimethoxyacetophenone (19) was used for most of the preparative work. The unexpected formation of an acid-labile dimer of 13 was discovered and solid state 13C nmr was used for structural assignment. The 5-methoxy substituent in these systems shows anomalous spectral characteristics and, in one case, was cleaved in acid media to 22.