Development of Biisoquinoline-Based Chiral Diaminocarbene Ligands:  Enantioselective S_N2‘ Allylic Alkylation Catalyzed by Copper−Carbene Complexes

Abstract

Chiral biisoquinoline-based diaminocarbene ligands (BIQ) were designed to create a chiral environment extended toward the metal center, which was confirmed by an X-ray structure. The concise ligand synthesis is highlighted by a modified Bischler-Napieralski cyclization of bisamides prepared from readily available chiral phenethylamines, and allows easy variation of the stereodifferentiating groups. The cyclohexyl-BIQ-copper complex is an efficient catalyst for enantioselective SN2' allylic alkylation with Grignard reagents showing SN2' regioselectivity higher than 5:1 and enantioselectivity in the range of 68-77% ee.

Crossed Regio‐ and Enantioselective Iron‐Catalyzed [4+2]‐Cycloadditions of Unactivated Dienes

“…We hypothesized that the increased rigidity of tethering ligand backbone and side‐arms may result in improved selectivities. In this respect, we envisioned that a chiral bis ‐dihydroisoquinoline scaffold, previously employed as synthetic intermediate for NHCs [31] and diazaphospholanes, [32] could be used as diimine ligand platform. In this respect, second generation catalyst ( S , S )‐ Fe7 equipped with cyclohexyl side‐arms provided a convincing performance (entry 11).…”

Highly Enantioselective Direct Synthesis of Endocyclic Vicinal Diamines through Chiral Ru(diamine)‐Catalyzed Hydrogenation of 2,2′‐Bisquinoline Derivatives

“…As shown in Scheme , AH of 1 a was carried out on a gram scale to give (2 S ,2′ S )‐ 2 a in 89 % yield of isolated product with >99 % ee . Subsequent treatment of (2 S ,2′ S )‐ 2 a with triethyl orthoformate and NH 4 BF 4 provided the key benzimidazolium tetrafluoroborate (2 S ,2′ S )‐ 4 a in quantitative yield, providing a facile and practical approach to a new class of rigid NHC ligands, which might be useful for asymmetric catalysis ,–. Similarly, several other benzimidazolium salts were synthesized in good yields.…”

Development of Quinoline-Derived Chiral Diaminocarbene Ligands and Their Transition Metal Complexes: Synthesis, Structural Characterization, and Catalytic Properties

“…13 C NMR (100 MHz, CDCl 3 ): δ (ppm) 210.6 (Rh−C (carbene) , J = 48.3 Hz), 139. 9,139.7,138.6,134.8,133.2,132.2,129.3,128.2,127.1,126.5,125.8,125.1, , J = 7.0 Hz), 97.6 (Rh−C (CC) , J = 7.0 Hz), 71.9 (Rh−C (CC) , J = 14.1 Hz), 67.7 (Rh−C (CC) , J = 14.1 Hz), 66. 9, 65.1, 34.1, 31.3, 30.3, 29.6, 29.2, 26.9, 26.8, 26.1, 22.4, 19.5 ,63.45;H,6.24;N,5.10.…”