Synthesis of Isoquinolone, 1,2-Benzothiazine, and Naphtho[1′,2′:4,5]imidazo[1,2-a]pyridine Derivatives via Rhodium(III)-Catalyzed (4 + 2) Annulation

Abstract

In this study, we report a novel and efficient synthetic method to construct isoquinolone scaffold via the Rh­(III)-catalyzed (4 + 2) annulation of benzamide with an unreported coupling reagent methyl 2-chloroacrylate. Accordingly, other valuable 1,2-benzothiazine and naphtho­[1′,2′:4,5]­imidazo­[1,2-a]­pyridine derivatives are also obtained through a similar synthetic protocol. Thus, our developed method is highlighted by high yield and reaction versatility.

Synthesis and site selective C–H functionalization of imidazo-[1,2-a]pyridines

“…Recently, Liu and his group succeeded in achieving a rhodium catalyzed [4 + 2] annulation study, to publish a novel and effective reaction of 2-arylimidazo[1,2- a ]pyridine 5 with methyl-2-chloroacetate 10 as a coupling reagent to afford naptho-[1′,2′:4,5]imidazo[1,2- a ]pyridine compounds 11 (Scheme 2). 45…”

“…44 Recently, Liu and his group succeeded in achieving a rhodium catalyzed [4 + 2] annulation study, to publish a novel and effective reaction of 2-arylimidazo[1,2-a]pyridine 5 with methyl-2-chloroacetate 10 as a coupling reagent to afford naptho-[1′,2′:4,5]imidazo[1,2-a]pyridine compounds 11 (Scheme 2). 45 In addition to carbon-carbon bond formation, the Sabitha group in 2016 achieved direct carbon-nitrogen bond formation and reported a general two-step technique for the preparation of innovative pyrido[2′,1′:2,3]imidazo[4,5-c]cinnoline derivatives 13 in good yields by the use of simple starting materials and mild reaction conditions to form two new C-N bonds via the C-H functionalization of 2-phenylimidazo[1,2-a]pyridines 12. Under the present conditions, the reaction went through hydrazination through diisopropyl azodicarboxylate (DIAD) followed by an oxidative N-arylation facilitated by phencyclidine diacetate (PIDA) in CF 3 COOH (Scheme 3).…”

Ru(II)-Catalyzed C(sp2)–H Activation Annulation: Synthesis of Fluorescent Benzoisoquinolonyl Acetate/Peptides from N-Arylamides and Ethyne at Room Temperature

“…The transition metal-catalyzed regioselective C–H activations of core aromatic/aliphatic molecules are extensively reported by installing directing groups . Various transition metal catalyst have been used for the synthesis of isoquinolone derivatives from aryl amide and ethyne molecules via C–H activation annulation. − A fascinating example is the atroposelective synthesis of biaryl by Rh­(III)-catalyzed C–H activation and intermolecular coupling with sterically hindered alkynes . Methoxybenzamide and vinylene carbonate, equivalent to acetylene, have also been utilized for the synthesis of isoquinolone derivatives by Rh­(III)-catalyzed C–H activation annulation at room temperature .…”