Planar Chiral [2.2]Paracyclophane-Based Bisoxazoline Ligands and Their Applications in Cu-Mediated N–H Insertion Reaction

Abstract

New catalysts for important C–N bond formation are highly sought after. In this work, we demonstrate the synthesis and viability of a new class of planar chiral [2.2]paracyclophane-based bisoxazoline (BOX) ligands for the copper-catalyzed N–H insertion of α-diazocarbonyls into anilines. The reaction features a wide substrate scope and moderate to excellent yields, and delivers the valuable products at ambient conditions.

The concise synthesis and resolution of planar chiral [2.2]paracyclophane oxazolines by C–H activation

“…There are numerous reports describing the utility of [2.2] paracyclophane oxazolines. They have been used as preligands, 16,[18][19][20]29 or have directed further functionalisation of the [2.2]paracyclophane by either bromination 16,23 or metalation. 19,21 We believe straightforward elaboration of the amine or acid functionality will deliver modular pre-ligands, but here we want to increase the versatility of the oxazoline moiety and present preliminary results on the hydrolysis and decarboxylative phosphorylation of the oxazolines.…”

“…11,12 Oxazolines form a host of 'privileged' pre-ligands, [13][14][15] and it is no surprise that numerous oxazoline-substituted [2.2]paracyclophanes 5 have shown potential in asymmetric catalysis. [16][17][18][19][20] The oxazoline moiety aids the synthesis of these compounds, either by permitting resolution of the planar chirality, [16][17][18][19]21,22 or by directing functionalisation of the cyclophane backbone. 16,19,21,23 Every one of these oxazoline-containing [2.2]paracyclophanes 5 was synthesised from a bromo derivative 2 via the carboxylic acid 3, then the amide 4, and nally cyclisation (Scheme 1).…”

“…The pseudo-para isomer, 4,16-bis(4 0 -benzyloxazolin-2 0 -yl)[2.2]paracyclophane 11a, is formed as a single stereoisomer due to its symmetry. The diastereoisomers of the more useful pseudo-ortho benzylsubstituted oxazoline 11b were readily resolved, 17,20,29 but only one diastereoisomer of the tert-butyl derivative 11c could be isolated. The other diastereoisomer co-ran with the two diastereomers of the product of protodebromination (8c).…”

Organocatalytic Desymmetrization Prompts Central-to-Planar Chirality Transfer to [2.2]Paracyclophanes

“…License: CC BY-NC-ND 4.0 focused on the unique 3D structure of chiral [2.2]paracyclophanes for their unusual electronical 11,12 and photophysical properties. [13][14][15][16][17][18][19] Case in point, highly rigid planar chiral [2.2]paracyclophanes (Figure 1) have become a valuable toolbox for developing ligands [20][21][22][23][24] and organocatalysts. 25 Beyond synthetic chemistry, these scaffolds have also been applied in small-organic circularly polarized luminescence (CPL, Figure 1D) [26][27][28] and other phosphorescent emitters.…”

Stereoselective synthesis of homochiral paracyclophanylindenofuranylimidazo[3.3.3]propellanes

“…Chiral mono-substituted [2.2]paracyclophanes play an important role and sometimes exhibit high enantioselectivities as chiral ligands [15][16][17][18][19]. In general, Rp and Sp were used to define the planar chirality present in [2.2]paracyclophane derivatives [20].…”