Although Cp*Rh(III) complexes are prominent and versatile catalysts for C-H bond functionalization reactions, catalytic stereocontrol is difficult due to the lack of vacant coordination sites. Here we report a hybrid strategy for inducing chirality without using previously reported chiral Cp x ligands. A preformed hybrid catalyst, [Cp*RhL N ][6,6'-Br-(S)-BINSate], catalyzed C-H activation and subsequent conjugate addition of 2-phenylpyridine derivatives to enones in good yield and enantioselectivity (up to 95:5 er). In addition to 2-phenylpyridines, conjugate addition of 6-arylpurines proceeded in up to 91:9 er using [Cp*RhL N ][(R)-SPISate]. The results demonstrated that a chiral organic anion can efficiently control the enantioselectivity of Cp*Rh(III)-catalyzed C-H bond functionalization without a chiral Cp x ligand. Transition metal catalysts cleave inert carbon-hydrogen (C-H) bonds in organic molecules to form reactive organometallic intermediates, enabling catalytic transformation of C-H bonds to desired carbon-carbon and carbon-heteroatom bonds. This catalytic C-H bond functionalization strategy can facilitate the development of atom-1 and step-economical 2 syntheses of functional molecules, and thus has been intensively investigated over the several decades. 3-16 Among various types of transition metal catalysts studied for catalytic C-H bond functionalization, Rh(III) complexes bearing a pentamethylcyclopentadienyl (Cp*) or related cyclopentadienyl-type (Cp,
We report enantioselective 1,4‐addition reactions of indoles to maleimides via a C2‐selective C−H activation catalyzed by an achiral Cp*CoIII/chiral carboxylic acid system. In these reactions, a BINOL‐derived chiral carboxylic acid enables the enantioselective reactions as the sole chiral source.
An
enantioselective [4+3] cyclization via C(sp2)–H
activation with a cooperative catalytic system consisting of a Cp*Rh(III)
complex and a chiral Lewis base is described. An α,β-unsaturated
acyl ammonium intermediate is generated from a chiral isochalcogenurea
catalyst and an acyl fluoride reacts with a metallacycle generated
from the Cp*Rh catalyst and a benzylamine derivative. This cooperative
catalytic system gives a variety of benzolactams in good yields with
excellent enantioselectivities (up to 99:1 er). The results demonstrated
that chiral Lewis base catalysis is a powerful tool for controlling
the enantioselectivity of transition metal-catalyzed C–H functionalizations.
1,1'-Spirobiindane-7,7'-disulfonic acid (SPISA) and 1,1'-spirobiindane-7,7'-disulfonimide were synthesized from 1,1'-spirobiindane-7,7'-diol (SPINOL) in 4 steps using a Pd-catalyzed Newman-Kwart rearrangement as a key step. These new catalysts possessing a rigid spirocyclic backbone were evaluated in a catalytic asymmetric aminalization reaction, and SPISA/iPr NEt exhibited high enantioselectivity, demonstrating the utility of SPISA as a chiral Brønsted acid catalyst.
Transition‐metal‐catalyzed directed C−H functionalization reactions are a powerful method to construct N‐heterocycles. However, compared to the formation of five‐ and six‐membered rings, that of seven‐membered rings has been much less explored. Here, the synthesis of benzo[c]azepine‐1,3(2H)‐diones is described, which are benzene‐fused seven‐membered imides, from hydroxamates and α,β‐unsaturated acyl fluorides via C−H activation using a Cp*Rh(III) catalyst. Under mild reaction conditions, this reaction affords benzo[c]azepine‐1,3(2H)‐diones that bear a substituent at the 5‐position.
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