On-Water Cp*Ir(III)-Catalyzed C–H Functionalization for the Synthesis of Chromones through Annulation of Salicylaldehydes with Diazo-Ketones

Abstract

A high-valent Ir(III)-catalyzed C−H bond functionalization is carried out for the first time on water for the synthesis of a biologically relevant chromone moiety. The C−H activation and annulation of salicylaldehydes with diazocompounds provided the desired chromones. The synthesis of C3-substitution-free chromones has also been demonstrated by a one-pot decarboxylation by employing tert-butyl diazoester. C3 and C5 C−H activations of the product chromone are also carried out under different conditions for further diversification.

Transition‐Metal‐Catalyzed C−H Bond Functionalization of Arenes/Heteroarenes via Tandem C−H Activation and Subsequent Carbene Migratory Insertion Strategy

“…An 'on-water' Ir(III)-catalyzed CÀ H bond functionalization of salicylaldehydes to construct biologically important chromone moieties has been reported by Maji and co-workers in 2019 (Scheme 43b). [138] Upon coupling with α-diazo-βketoesters, C(2)/C(3)-di-substituted chromones are synthesized in good yields, whereas tert-butyl derivative of α-diazo-βketoester produces C(2)-substituted products solely through a one-pot decarboxylation strategy. Hence, a diversified strategy for introducing selective substitution pattern on the chromone unit has been developed within a green solvent system.…”

Sustainable C–H functionalization under ball-milling, microwave-irradiation and aqueous media

“…This hurdle was recently overcome by Maji’s group when they developed a water-mediated Ir( iii ) C–H annulation of salicyaldehydes, with diazo compounds providing the required chromones, in 2019 (Scheme 32). 81 Under the iridium catalytic system, the coupling of salicyaldehydes with ethyl diazoacetate in the presence of acetic acid (1.0 equiv.) as an additive was carried out at 80 °C, and gave a yield of 70% of the coupling product.…”

Green strategies for transition metal-catalyzed C–H activation in molecular syntheses

“…Water itself has been found applications as a reaction medium for a variety of C-H bond functionalization reactions, catalyzed by palladium, 53 rhodium, 54 iridium 55 and ruthenium. 56 Similarly, water has also been found as an amenable solvent for Earth-abundant 3d metal-catalyzed C-H functionalization.…”