Iron‐Catalysed C(sp²)‐H Borylation with Expanded Functional Group Tolerance^†

Abstract

Arene C(sp 2 )-H bond borylation offers direct and efficient access to aryl boronic esters. Using in situ catalyst activation and photoirradiation, the iron-catalysed C(sp 2 )-H borylation reaction of carboarenes, pyrroles, and indoles has been developed using only benchstable pre-catalysts and reagents. Good functional group tolerance was observed including those not tolerated under previous methods (ArNH2, ArOH, ArSiR3, ArP(O)(OR)2, ArC(O)NR2). Mechanistic studies revealed iron-catalysed reductive deoxygenation, C-F protodefluorination, and a demethylation of aryl methyl ethers by C-O sigma bond hydroboration.

Access to C(sp3) borylated and silylated cyclic molecules: hydrogenation of corresponding arenes and heteroarenes

“…1 H and 13 C{ 1 H} NMR data were consistent with those previously reported 61 and 11 B NMR data were also consistent those previously reported. 62 (Note: ref. 47 reports the Bpin at 1.54 in the tabulated data however in the spectrum provided the peak appears at 1.34 ppm.…”

“…1 H and 13 C{ 1 H} NMR data were consistent with those previously reported 61 as were 11 B NMR data. 62 (Note CDCl 3 reference reported in ref. 47 was set at 78.1 instead of 77.2 thus their tabular data are shifted by 1.0 ppm relative to ours.…”

Iron‐Catalyzed Reductive C(aryl)—Si Cross‐Coupling of Diaryl Ethers with Chlorosilanes

“…Iron catalysis has emerged as a powerful methodology for construction of C—C bond by cross‐coupling reactions. [ 58‐70 ] In particular, low‐valent iron catalysts often showed unique activity and selectivity in the coupling reactions of various unactivated carbon electro‐philes, [ 58‐59,62,65,68,70‐78 ] such as the couplings of aryl esters [ 72‐73 ] and ethers [ 77 ] via the activation of C(aryl)—O bonds. Very recently, the interesting iron‐catalyzed cross‐electrophile coupling of aryl carbamates with alkyl bromides via C—O bond activation was reported by the Feng group.…”

Transition-Metal-Catalyzed C–H Bond Activation for the Formation of C–C Bonds in Complex Molecules

“…Chemical synthesis underpins the evolution and advancement of broad areas of science from materials to medicines. − Transition-metal-catalyzed synthetic transformations offer broadly applicable strategies for the discovery and development of new and useful molecules that have served in diverse applications. − However, the typical use of modern transition-metal-catalyzed synthetic methods has relied on the presence of prefunctionalized starting materials to control both chemo- and regio-selectivity. − This has presented an inherent challenge given that the pool of prefunctionalized precursors is significantly smaller than that of unfunctionalized feedstock chemicals. , Additionally, the requirement of prefunctionalization before a specific synthetic transformation is enabled limits applicability to the vast selection of already complex and heavily diversified molecules such as natural products or pharmaceuticals. To address this limitation a broad range of methods for the installation of synthetically useful functional handles have been developed, many of which rely on multistep procedures and conjointly lead to limited overall sustainability due to reduced step-economy, synthetic inefficiency, and waste. − …”