Iridium‐Catalysed C−H Borylation of Heteroarenes: Balancing Steric and Electronic Regiocontrol

Abstract

Scheme 5. Ir-catalyzed CÀH borylation of arenes. mtbe = methyl tert-butyl ether [IUPAC: 2-methoxy-2-methylpropane]. Scheme 4. Catalytic cycles of the Ir-catalysed CÀH borylation depicting catalyst regeneration using B 2 pin 2 (blue) and HBpin (red). coe = cyclooctene.

Selectivity in the Elaboration of Bicyclic Borazarenes

“…C−H Functionalization : As in the case of the C−H borylation of 2,1‐borazaronaphthalene, we can calculate the site of greatest anionic stability as a potential site of reaction selectivity, given that steric constraints are satisfied [9m,21a,c] . As expected, the position most favored for borylation is influenced strongly by proximity to heteroatoms, and can also be swayed by steric factors and substitution patterns.…”

Metal‐Free Directed C−H Borylation of Pyrroles

“…Especially for C3‐substituted pyrroles, the selectivity of the C2 and C5 positions constitutes a prototypical example of such an issue. As one of the most notable advances in C−H functionalization, C−H borylation [7] has been conducted with pyrroles [5a, 8] by transition metal catalysis [9] . To the best of our knowledge, only one example of the C−H borylation of a C3‐substituted pyrrole containing an ester group has been recently reported with an iridium catalyst, in which the regioselectivity is preferentially located at the less hindered C5 position (Figure 1 a).…”

“…As one of the most notable advances in CÀH functionalization, CÀH borylation [7] has been conducted with pyrroles [5a, 8] by transition metal catalysis. [9] To the best of our knowledge, only one example of the C À H borylation of a C3substituted pyrrole containing an ester group has been recently reported with an iridium catalyst, in which the regioselectivity is preferentially located at the less hindered C5 position (Figure 1 a). [10] The introduction of a directing group at the N-atom can position the metal catalyst near a particular C À H bond through cyclometallation.…”

Iridium-catalysed 3,5-bis-borylation of phthalonitrile enables access to a family of C4h octaarylphthalocyanines

“…A recurring issue in Pc chemistry is that the synthesis of substituted phthalonitrile precursors is often lengthy and hindered by the low reactivity of electron-poor phthalonitrile in S E Ar reactions. Here, we report our initial investigation into the use of sterically controlled Ir-catalysed C-H borylation [10][11][12] to functionalize phthalonitrile that circumvents its unfavourable electronics. This study was further motivated by the ease with which aryl boronic acid pinacol ester (Bpin) groups introduced by this reaction might, in general, be converted to a wide range of other functional groups, including various amines, ethers, thioethers, (hetero)arenes, or to an azide, halide, nitro or alcohol group for further functionalization using known transformations.…”