Phthalazines. XV. Ring Transformation of Phthalazines into Naphthalenes by Means of Inverse-Electron-Demand Diels-Alder Reaction

The 1-substituted phthalazines 6 underwent inverse-electron-demand Diels-Alder reaction with the enamines 3 and ynamines 9, resulting in the formation of 1-substituted naphthalenes.Thus, 1-phthalazinecarbonitrile (6b) reacted with 3a-i to give the corresponding 1-naphthonitriles 7a-e, g, h and 2, 3-kihydro-1-naphthonitriles 8f, i, respectively. Similarly, reaction of 1-(methylsulfonyl)phthalazine (6c) with 3a, b, d, f gave the corresponding 1-(methylsulfonyl)naphthalenes 10a, b, d and 1-(methylsulfonyl)-2, 3-dihydronaphthalene 11f. Furthermore, 1-methylthio- (6e), 1-phenyl- (6f), 1-methyl-(6b), 1-chlorophthalazines (6h) and phthalazine (6a) reacted with 3a to afford the corresponding 4-substituted 2, 3-dihydro-1H-benz[f]indenes 12e-h, a, respectively.A similar ring transformation was found to proceed between 1, 4-phthalazinedicarbonitrile (14) and 1-methyl-1H-indole (13), giving the benzo[b]carbazoledicarbonitrile (15).Compounds 6b and 6c also underwent inverse-electron-demand Diels-Alder reaction with the ynamines 9a, b to give the corresponding 1-cyano-16a, b and 1-(methylsulfonyl)naphthalenes 17a, b, respectively.