6,8-Dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-dione: a novel method of pyrrole-ring annulation to an azine nucleus based on a tandem SNH–SNH process

Pyrimido[4,5-c]pyridazine-5,7(6H, 8H)-diones: Marvelous substrates for study of nucleophilic substitution of hydrogen

“…Thus, compound 1 reacted with diethylamine unexpectedly produced the condensed pyrrole 8_ as a single product in 42% yield (Scheme 6) [16]. The structure of 8a has been confirmed by X-ray study.…”

Oxidative alkylamination of aromatic and heteroaromatic substrates and accompanying heterocyclization reactions

“…However, in reactions of com pound 20 with acyclic secondary amines in the presence of AgPy 2 MnO 4 , the sole products are fused pyrroles 34 (Scheme 26). 50 As nucleophiles, acyclic dialkylamines are not very reactive in oxidative alkylamination but they are highly oxidizable; because of this, the reaction follows an unex pected pathway. The transformation 20→34 starts with the oxidation of dialkylamine into imine 35 that is in equilibrium with enamine 36 (Scheme 27).…”

“…50 The transformation 20→34 is not only a rare example of tandem S N H S N H processes but also a novel route to fused pyrroles. However, amination of compound 40 with cyclohexyl amine or isopropylamine gives, along with the corre sponding 3 amino derivatives 41e,g, imidazolines 43a,b in ~5% yields (Scheme 30).…”

σH-Adducts of N-alkylpyrazinium and quinoxalinium salts with nucleophiles. The 1H and 13C NMR spectra and the crystal structures of P-adducts

“…[9][10][11] In recent years, the development of new methods for the synthesis and modi fications of diazines, including methods based on the direct nucleophilic attack on the unsubstituted carbon atom of the azine ring, has attracted great attention. [12][13][14][15][16][17][18][19] It is known that N alkylpyrazinium and quinoxalinium salts are prone to the mono and diaddition of O , C , N , and S nucleophiles, as well as to annulation of five or six membered heterocycles in reactions with a wide range of dinucleophiles. 12- 14 Primary σ H adducts, which are generated via the nucleophilic attack on the α position with respect to the cationic center, were comprehensively characterized by 1 H and 13 C NMR spectroscopy.…”