Chiral Bicyclo[2.2.2]octane‐Fused CpRh Complexes: Synthesis and Potential Use in Asymmetric C−H Activation

Abstract

A new class of chiral cyclopentadienyl rhodium(I) complexes (CpRhI) bearing C2‐symmetric chiral bridged‐ring‐fused Cp ligands was prepared. The complexes were successfully applied to the asymmetric C−H activation reaction of N‐methoxybenzamides with quinones, affording a series of chiral hydrophenanthridinones in up to 82 % yield with up to 99 % ee. Interestingly, structure analysis reveals that the side wall of the optimal chiral CpRhI catalyst is vertically more extended, horizontally less extended, and closer to the metal center in comparison with the classic binaphthyl and spirobiindanyl CpRhI complexes, and may thus account for its superior catalytic performance.

Rhodium‐Catalyzed C−H Activation‐Based Construction of Axially and Centrally Chiral Indenes through Two Discrete Insertions

“…To our delight, nitrones bearing as eries of ortho electron-donating,-withdrawing,a nd bulky substituents all reacted in excellent enantioselectivity and good efficiency (4)(5)(6)(7)(8), which stayed contrast to limited compatibility of ortho groups in most CÀHactivation systems. Thep resence of diverse meta and para substituents in the benzene ring was also well tolerated (9)(10)(11)(12)(13)(14)(15)(16). The N-benzyl group in the nitrone was been extendable to substituted ones, and the enantioselectivity was constantly excellent although the coupling efficiency varied (17)(18)(19)(20)(21).…”

“…[7][8][9] Ther eaction can be annulative, [7] transannulative, [8] and nonannulative, [9] and the enantioselective control roots in stereospecificity of the olefin insertion that generates two correlated chiral centers.I n addition, C À Hactivation may generate the first chiral center that induces the second chiral center (Scheme 1b). [10] Occasionally,d esymmetrization of arenes can be employed, and the desymmetrization event leads to formation of ac hiral center, and subsequent CÀHf unctionalization gives another chiral center or axis (Scheme 1c). [11] Despite the significant progress,t he multiple chiral elements in these products are mostly created in acorrelated manner,and it is challenging to generate two discrete chiral elements using the same chiral catalyst in asingle reaction, especially when the second chiral element is rendered without induction of the first one and when they are distal to each other.…”

Oxygen‐Linked Cyclopentadienyl Rhodium(III) Complexes‐Catalyzed Asymmetric C−H Arylation of Benzo[h]quinolines with 1‐Diazonaphthoquinones

“…While cyclopentadienyl (Cp) rhodium complexes stood out as privileged catalysts in CÀHfunctionalization reactions over the past decade, [1] their enantioselective variants remained to be challenging due to the difficulty on modifying chiral Cp ligands.In2012, the groups of Ward and Rovis,and the Cramer group have made significant breakthroughs in CpRh-catalyzed asymmetric C À Hfunctionalization reactions via biochemical and chemical modifications of the Cp ligands independently. [2] Soon afterwards,s everal elegant chiral Cp ligands have been developed, [3] including spirobiindanyl Cp (B), [4] piperidine-fused Cp (C), [5] bicyclo[2.2.2]octane-fused Cp (D), [6] and others (Figure 1), [7][8][9][10] which inspired further developments of chiral Cps for enantioselective C À Hf unctionalization processes.T ob en oted, binaphthyl chiral Cp ligands (A)were pioneeringly designed by the Cramer group, and av aluable array of transformations have been successfully achieved based on these C-linked ligands. [11] More recently,o ur group synthesized sterically and electronically tunable binaphthyl Cp ligands by using Co 2 (CO) 8 mediated [2+ +2+ +1] cyclization as ak ey step,a nd these ligands have facilitated the efficient synthesis of isoindolinones by enantioselective [4+ +1] annulation reaction of benzamides with alkenes.…”

A Class of Readily Tunable Planar‐Chiral Cyclopentadienyl Rhodium(III) Catalysts for Asymmetric C–H Activation

“…As shown in Figure 1b, a variety of elegant chiral Cp ligands have been prepared by this way during the last decade, including the artificial-enzyme-bound Cp A, [4] cyclohexane-fused Cp B, [3] biaryl Cp C, [5] cyclopentane-fused Cp D, [6] spirobiindanyl Cp E, [7] piperidine-fused Cp F, [8] myrtenal derived Cp G, [9] ferrocenyl Cp H, [10] and bicyclo[2.2.2]octane-fused Cp I. [11] The second type of chiral CpRh III catalysts is planar-chiral only, which is derived from non-chiral but prochiral Cp ligands (Figure 1a, type II). However, in sharp contrast to the great success achieved in the type I catalyst, the type II catalyst is largely underdeveloped due to its high challenges.…”

“…Since catalysts J, K or L are hard to modify, their applications may be greatly restricted. With our continuous interest in developing new chiral CpRh III catalysts, [10,11] we would like to present herein a class of readily tunable planar-chiral CpRh III catalysts bearing non-chiral Cp ligands (Figure 1c). Notably, this class of catalyst has been successfully applied in two asymmetric CÀ H activation reactions.…”