Substituted coumarin amidines: useful building blocks for the preparation of [1]benzopyrano[4,3-b]pyridin-5-one and [1]benzopyrano[4,3-d]pyrimidin-5-one derivatives

The synthesis of [1]benzopyrano[4,3-b]pyridin-5-ones 4a-f and 4g-j starting from 3-formylcoumarin and 3-cyanocoumarin N-functionalized amidines 3a-f and 3g-j, respectively, was reported. The ring-closure reaction mechanism, under basic or acidic media, was proposed. Furthermore, the reaction of 3-formylamidines 3a,c-f with ammonium acetate gave good yields of 2-substituted [1]benzopyrano[4,3-d]pyrimidin-5-oiies 7. (c) 2005 Elsevier Ltd. All rights reserved.