Cp*Co(iii)-catalyzed annulation of azines by C–H/N–N bond activation for the synthesis of isoquinolines

Abstract

An atom economic and external oxidant free methodology has been developed for the synthesis of isoquinolines by Cp*Co(iii) catalyzed annulation of azines via C–H/N–N activation.

Rhodium-Catalyzed C(sp2)–H Amidation of Azine with Sulfonamides

“…Encouraged by these results, we next moved to screen the azine substrates for the given reaction (Table ). Azine derivatives ( 1a–1l ) were prepared according to the previously reported procedures. − The amidation conditions were compatible with various functional groups such as fluoro, chloro, bromo, and trifluoro (Table , entries 3ca–3fa ). Electronic variation of substituents on the para positions of the phenyl rings did not have much influence on the reaction efficiency (Table , entries 3ba and 3ga ).…”

“…The synthesis of aromatic azines 1a–1l was done according to the previously reported procedures; their spectral characterization and other physical data matched those reported previously. − Hydrazine hydrate (1.0 g, 10 mmol, 50%) was added to a solution of acetophenone (1.2 g, 10 mmol) and AcOH (60.0 mg, 1.0 mmol) in EtOH (10 mL), and then the mixture was heated in a preheated oil bath to 100 °C with stirring and refluxed for 10 h. After cooling to room temperature, the mixture was filtered, washed with EtOH (20 mL × 4), and dried under vacuum. A yellow solid (1 E ,2 E )-1,2-bis­(1-phenylethylidene)­hydrazine 1a was obtained in 87% yield.…”

“…Recently, scientists have reported that azine can be used as a directing group to construct C–S and C–C bonds through C–H activation (Scheme ). Nevertheless, the formation of a C–N bond with the cleavage of C–H bonds with the azine group as a directing group remains undeveloped.…”

Comprehensive Strategies for the Synthesis of Isoquinolines: Progress Since 2008

“…Various azine derivatives and symmetrical alkyne or unsymmetrical alkynes 69 were employed under these reaction conditions to obtain isoquinolines 74 in high yields (Scheme 57). [85] Choi et al have developed a γ-selective CÀ H allylation/hydroamination protocol for the synthesis of 3,4-dihydroisoquinoline 105 a under cobalt(III)-catalyzed reaction conditions utilizing NH ketimines 93 and allyl carbonates 104 as starting materials (Scheme 58). [86] Scheme 54.…”

“…Various azine derivatives and symmetrical alkyne or unsymmetrical alkynes 69 were employed under these reaction conditions to obtain isoquinolines 74 in high yields (Scheme 57). [85] …”