Friedländer reaction of 3-acetyltropolones: Synthesis of naphthyridinyl- and allied heterocyclic-substituted tropolones

Five 3-acetyltropolones reacted with 2-amino-3-pyridinecarbaldehyde to afford the corresponding 3-(1,8-naphthyridin-2-yl)tropolones in excellent yields. In a similar manner, 1,6-naphthyridin-2-yl-,1,7-naphthyridin-2-yl-, 6-pyrido2,3-b]pyrazinyl-, and 1-methyl-6-pyrazolo5,4-b]pyridyl-substituted tropolones were prepared. Reactivities of amino-substituted heteroarenecarbaldehydes in these reactions and properties of the products are also discussed.