Palladium-Catalyzed Oxidative Annulation of Pyrrolylalkyl-1H-azoles: Towards the Synthesis of Polyheterocyclic Arenes

Abstract

A highly efficient and regioselective palladium-catalyzed annulation protocol for a series of linear and terminally substituted 1,2- and 1,3-di(heteroaryl)alkanes to the corresponding polyheterocyclic arenes is reported. Herein, intramolecular oxidative coupling involving double C(sp2)–H bond functionalization provides a feasible access to biheteroaryl systems annulated to a six-membered ring. The methodology is not restricted to six-membered annulations and was extended to the synthesis of compounds with a seven-membered ring and biheteroaryl core.

Solvent Moisture-Controlled Self-Assembly of Fused Benzoimidazopyrrolopyrazines with Different Ring’s Interposition

“…Table 3. Structures of 5-methylbenzo [4,5] The reaction was found to be of general character. It was shown that aromatic and heteroaromatic substituents did not affect yields of the products ( 6a-i, k-l).…”

“…Scheme 2. Synthesis of 6-methyl-3-phenylbenzo [4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazine and 5a-methyl-3-phenyl-5a,6-dihydro-5H,12H-benzo [4,5]imidazo[1,2-a]pyrrolo[1, 2-d]pyrazine.…”

“…Probably, water here directly affects the direction of Cannizzaro reaction and somehow Scheme 6. Possible pathway 2 of formation of 5a-methyl-5a,6-dihydro-5H,12H-benzo [4,5]…”

“…The formed precipitate was filtered off. 3-Butyl-6-methyl-2-propylbenzo [4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazine (3a). White powder (0.078 g, 30% yield; 0.147 g, 42% yield).…”

“…They can be divided into two groups: intramolecular and intermolecular reactions (Scheme 1). Polyheterocyclic systems are obtained via intramolecular cyclization in the presence of palladium [5] or copper [6,7] salts as catalysts at high temperatures. Intermolecular cyclizations are also promoted by catalysts: transition metals [8], salts [9] or acids [10].…”