Novel cyclization reactions of dichloroazodienes

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

“…For the synthesis of cinnoline derivatives, aryldiazenes and aryltriazenes are substrates of choice for transition-metal-catalyzed (Rh, Pd, Cu) cross-coupling reactions, followed by intramolecular cyclizations [44][45][46][47]. Moreover, arylhydrazones and arylhydrazines/hydrazines can be used as well, respectively, as partners in [4 + 2] cyclization reactions [48][49][50][51] or by reacting mostly with carbonyl derivatives [52][53][54][55].…”

Six‐Membered Heterocycles: 1,2‐, 1,3‐, and 1,4‐Diazines and Related Systems

“…Wan and Snyder have applied this strategy to the inverse-electron demand cycloadditions of 2-substituted imidazoles 61 with 1,2,4,5-tetrazine-3,6-dicarboxylate, 62, to afford imidazo [4,5-d] This methodology has been extended to solid-phase synthesis for the rapid assembly of pyridazine compound libraries (Scheme 19.28). A resin-bound aminotetrazine with a functional group at the C6 position (64) has been used in combination with a wide range of electron-rich dienophiles to give pyridazines 65 after cleavage from the solid support [59]. …”

“…These [4 þ 2]-cycloaddition reactions show a high degree of regio-and stereochemical control [62,63]. The primary reaction products are tetrahydropyridazines but they can be oxidatively transformed into the fully aromatic compounds (Scheme 19.31) [64]. Aromatic furans have been reported to undergo synthetically useful ring transformation into pyridazines in two steps [65].…”

Addition and Cycloaddition Reactions of Phosphinyl- and Phosphonyl-2H-Azirines, Nitrosoalkenes and Azoalkenes

“…A more recent work [ 61 ] using density functional theory (DFT) studies, showed a polar character of the Diels–Alder reaction of nitrosoalkenes with enamines, being the two σ bonds formed in these polar cycloaddition reactions in a highly asynchronous concerted process. On the other hand reactions of azoalkenes with enamines are solvent and structure – of enamine and azoalkene - dependent [ 1 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ], proceeding either via [4+2] cycloaddition or conjugate addition.…”