The Indenyl Effect: Accelerated C-H Amidation of Arenes via Weakly-Coordinating Group Directed Nitrene Transfer Catalysis

Abstract

Investigations into C-H amidation reactions using electron-deficient cationic half-sandwich d6 metal complexes revealed that the indenyl-derived catalyst [Ind*RhCl2]2 significantly accelerated the directed ortho C-H amidation of benzoyl silanes using 1,4,2-dioxazol-5-ones. Ring slippage involving a haptotropic rearrangement of the indenyl complex proposedly enables ligand substitution at the metal centre to proceed via associative, rather than dissociative pathways, leading to significant rate and yield enhancements. Intriguingly, this phenomenon appears specific for C-H amidation reactions involving weakly coordinating carbonyl-based directing groups with no acceleration observed for the corresponding reactions involving strongly coordinating nitrogen-based directing groups.

Photo-Induced Electrophilic Aromatic Substitution of Ferric Acyl Nitrene

“…9, 143.697, 133.5, 124.9, 124.0, 122.2, 115.1, 67.2, 20.8, 16.3. [1,4] oxazin-3(4H)-one (2h) 17 : The title compound was prepared according to the general procedure. The product was purified by flash chromatography (PE/EA = 4/1) to give 2h, white solid.…”

“…A solution of 2-(4-fluorophenoxy)-N-(pivaloyloxy) acetamide (0.3 mmol), FeCl3 (0.2eq) in 1,4 -dioxane (3.0 ml) was stirred under 455 nm blue light at 60 °C for 4.5 h. After the disappearance of substrate as indicated by TLC, the reaction solution was concentrated under reduced pressure and purified by rapid column chromatography to obtain the desired target product. [1,4] oxazin-3(4H)-one (2u') 17 : Minor isomer was purified by flash chromatography (PE/EA = 5/1) to give 2u'as white solid, 10 mg (19% yield); mp. : 204−207℃.…”

“…3 The established achievements suggested the accurate use of nitrene precursors and metal catalysts was responsible for the reaction efficiency and selectivity. 4 In 2021, Yu and co-workers employed αazido N-phenylamides as nitrene precursors, and through a skeleton rearrangement, a cycloaddition of nitrene with arene and sequential ring expansion towards azepin-2-ones were developed under iron catalysis (Scheme 1, eq a). 5 By altering to iridium catalyst, the use of dioxazolones as nitrene precursors underwent a dearomative ipsocyclization with arene, rather than cycloaddition (Scheme 1, eq b).…”

Sustainable chemical synthesis: making molecules using visible-light irradiation

“…In recent years, our research group has been investigating the reactivity and properties of a unique chemical functional group known as acyl silanes (Zhang et al 2013). We have demonstrated that acyl silanes can be used as directing groups for metal-catalysed C-H Priebbenow 2023;Priebbenow & Hua 2021). Acyl silanes can also undergo the Brook rearrangement when irradiated with blue light (using wavelengths between 390-440 nm).…”