Brønsted acid-mediated cyclization–dehydrosulfonylation/reduction sequences: An easy access to pyrazinoisoquinolines and pyridopyrazines

• Ramana Sreenivasa Rao and
• Chinnasamy Ramaraj Ramanathan

Beilstein J. Org. Chem. 2017, 13, 428–440, doi:10.3762/bjoc.13.46

• ; praziquantel; pyrazinoisoquinoline; pyridopyrazine; Introduction Piperazine is an important structural core found in many biologically active natural products [1]. Piperazines are also useful intermediates in the synthesis of a variety of drug molecules having important biological activities such as

• for the synthesis of many alkaloids (Figure 1) [16]. To synthesize pyrazinoisoquinoline and its derivatives, various approaches such as the Ugi multicomponent reaction [17] amidoalkylation [18][19], N-acyliminium ion cyclization [20] and a radical cyclization [21] have been reported. To this end

• corresponding products. Further, these 4-benzenesulfonylpiperazine-2,6-diones were subjected to an imide carbonyl group activation strategy, to develop a practical approach to synthesize pyrazinoisoquinoline and pyridopyrazines via Brønsted acid assisted 6-exo-trig cyclization of arylethylpiperazine-2,6-diones