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,

In the enantioselective inverse-electron-demand hetero-Diels-Alder reaction, simple α,β-unsaturated aldehydes (i. e., acroleins) are still challenging substrates, unlike α,β-unsaturated carbonyl compounds containing electronwithdrawing groups. In the present study, the reaction of α-aryl-β-alkyl-substituted acroleins with ethyl vinyl sulfide was developed with the use of bulky chiral supramolecular Brønsted acid catalysts, such as tris(pentafluorophenyl) borane-assisted chiral phosphoric acid catalysts. As a result, cis-cycloadducts as optically active 3,4-dihydro-2H-pyrans were exclusively obtained in high yields with high enantioselectivities via the favored endo orbital approach. An obtained optically active cis-isomer could be transformed into the corresponding trans-isomer without a loss of enantiopurity by O,S-acetal epimerization. Moreover, transformations to synthetically useful optically active epoxide and δ-valerolactone are also demonstrated.[a] Dr.

A highly chemoselective transesterification of methyl (meth)acrylates catalyzed by sterically demanding 2,6-di-tertbutyl-4-methylphenol (BHT)-derived NaOAr or Mg(OAr)2 was developed. The desired transesterification proceeded without undesired Michael additions under mild reaction conditions at 25 °C, and various primary and secondary alcohols, diols, triol, and tetraol on a scale of up to 10 mmol could provide the corresponding functionalized acrylates in high yields. Transition states were proposed based on monomeric and dimeric active species, and computational DFT calculations strongly supported the high chemoselectivity to minimize undesired Michael additions.

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The enantioselective aza-Friedel–Crafts reaction of indoles with low-reactive ketimines has been developed in the presence of a chiral monopotassium binaphthyldisulfonate as a strong Brønsted acid catalyst. A broad substrate scope was achieved, and the corresponding 3-indolylmethanamines with a chiral quaternary carbon center were obtained in high yields with high enantioselectivities. The addition of a catalytic amount of acetic acid considerably promoted the reaction, and a gram-scale reaction could be achieved with reduced catalyst loading.

BBr -assisted chiral phosphoric acid catalysts for enantioselective [2+2] cycloaddition were developed. The reactions of phenyl vinyl sulfide with α-substituted acroleins proceeded, and the corresponding [2+2] cycloadducts were obtained with high enantioselectivity. In particular, the [2+2] cycloadduct obtained from methacrolein is a synthetically useful optically active cyclobutane, which could be transformed to a key intermediate for (+)-frontalin, a pheromone of Asian elephants.

Highly enantio-and diastereoselective carbonyl-ene cyclization was developed with the use of chiral Lewis acid-assisted chiral Brønsted acid (LBA) catalysts, which were prepared in situ from both sterically demanding tris(pentafluorophenyl)borane and chiral phosphoric acids. Along with the performance of standard carbonyl-ene cyclizations, carbonyl-ene cyclization− acetalization tandem reactions with the use of additional aldehydes were demonstrated with high enantio-and diastereoselectivities. On the basis of mechanistic examinations, a stepwise reaction pathway via tertiary carbocation intermediates involving possible transition states is proposed.

A method for the synthesis of a bis-cyclometalated rhodium complex containing two different cyclometalating ligands is reported and applied to asymmetric catalysis. The preparation of this previously inaccessible class of tris-heteroleptic bis-cyclometalated rhodium­(III) complexes was achieved by a stepwise protocol that relies on the formation of an isolable mono-cyclometalated rhodium­(III) species in the first step, providing the opportunity to introduce a different second ligand in a subsequent additional cyclometalation step. The obtained racemic complex was resolved into its single enantiomers using an established chiral auxiliary ligand approach. The final Λ- and Δ-configured chiral-at-metal rhodium complexes contain a cyclometalated 5-tert-butyl-1-methyl-2-phenylbenzimidazole, a cyclometalated 5-tert-butyl-2-phenylbenzothiazole, and two acetonitrile ligands, complemented by a hexafluorophosphate counterion, and proved to be highly efficient for asymmetric [2 + 2] photocycloadditions.