A Traceless Chiral Shift Reagent Based on Nonbonding Interactions with Single-Handed Helical Poly(quinoxaline-2,3-diyl).

A single-handed poly(quinoxaline-2,3-diyl) (PQX) has been found to serve as a new type of chiral shift reagent (CSR) for determining the enantiomeric ratio by NMR spectroscopy. Even though there is no specific binding site in the PQX, its nonbonding interaction with chiral analytes leads to a significant shift of the NMR chemical shift, allowing quantification of the enantiomeric ratio. The new type of CSR has the advantages of a wide scope of analytes including ethers, haloalkanes, and alkanes, easy tunability of the degree of chemical shifts by measurement temperature, and erasability of proton signals of CSR because of the short spin-spin (T ) relaxation of the macromolecular scaffold.

Iridium-catalyzed enantioselective intramolecular hydroarylation of allylic aryl ethers devoid of a directing group on the aryl group.

Although intramolecular hydroarylation is an attractive transformation of allylic aryl ethers, it has suffered from narrow substrate scope. We herein describe Ir/()-DTBM-SEGPHOS-catalyzed intramolecular hydroarylation of allylic aryl ethers. The reaction eliminates the structural requirement from the aryl group, affording 2,3-dihydrobenzofurans bearing a stereogenic carbon center at the C3 position with up to 99% enantiomeric excess.

: Helical Poly(quinoxaline-2,3-diyl)s Bearing 4-(Dipropylamino)pyridin-3-yl Pendants as Chirality-Switchable Nucleophilic Catalysts for the Kinetic Resolution of Secondary Alcohols.

Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-(dipropylamino)pyridin-3-yl pendants at the 5-position of the quinoxaline ring () exhibited high catalytic activities and moderate to high selectivities (up to = 87) in the acylative kinetic resolution of secondary alcohols. The solvent-dependent helical chirality switching of between pure toluene and a 1:1 mixture of toluene and 1,1,2-trichloroethane enabled the preparation of either compound of a pair of enantiomerically pure alcohols (>99% ee) from a single catalyst.

Protected amino acids as a nonbonding source of chirality in induction of single-handed screw-sense to helical macromolecular catalysts.

Chiral nonbonding interaction with -protected amino acid methyl esters used as chiral additives in achiral solvents allows dynamic induction of single-handed helical conformation in poly(quinoxaline-2,3-diyl)s (PQX) bearing only achiral substituents. Ac-l-Pro-OMe, for instance, allows induction of energy preference of 0.16 kJ mol per monomer unit for the -helical structure over the -helix in -butyl methyl ether (MTBE).

Copper-catalyzed regioselective -silaboration of internal arylalkynes with stereochemical switch to -addition mode.

Copper-catalyzed silafunctionalization of alkynes using a silylboronic ester as a silicon source has recently progressed rapidly. Generally, the reaction affords a product with cis-stereoselectivity. We herein describe trans-selective 1,2-addition of silylboronic esters to internal arylalkynes, which was promoted efficiently by the CuOt-Bu/RCy2P/NaOt-Bu catalysts.

Enantioconvergent Cu-Catalyzed Intramolecular C-C Coupling at Boron-Bound C(sp) Atoms of α-Aminoalkylboronates Using a -Symmetrical 2,2'-Bipyridyl Ligand Attached to a Helically Chiral Macromolecular Scaffold.

Enantioconvergent intramolecular coupling of α-(2-bromobenzoylamino)benzylboronic esters was achieved using a copper catalyst having helically chiral macromolecular bipyridyl ligand, PQXbpy. Racemic α-(2-bromobenzoylamino)benzylboronic esters were converted into ()-configured 3-arylisoindolinones with high enantiopurity using right-handed helical PQXbpy as a chiral ligand in a toluene/CHCl mixed solvent. When enantiopure ()- and ()-configured boronates were separately reacted under the same reaction conditions, both afforded ()-configured products through formal stereoinvertive and stereoretentive processes, respectively.

Holding of planar chirality of pillar[5]arene by kinetic trapping using host-guest interactions with achiral guest solvents.

We report a solvent-dependent switching and holding of planar chirality of pillar[5]arene with stereogenic carbons at both rims by host-guest complexation with achiral guest solvents. The planar chirality could be held for a given length of time at 25 °C in long linear guest solvents by kinetic trapping through host-guest complexation. The kinetic trapping worked at 25 °C, but not at 60 °C, thus a planar-chiral inversion using kinetic trapping based on host-guest complexation in the long linear solvents was demonstrated.

Construction of Silicon-Containing Seven-Membered Rings by Catalytic [4 + 2 + 1] Cycloaddition through Rhodium Silylenoid.

A rhodium-catalyzed [4 + 2 + 1] cycloaddition involving 1,3-diene, alkyne, and silylene to afford silicon-containing seven-membered rings was established. In the presence of a rhodium catalyst bearing bis(diphenylphosphino)methane (DPPM), nona-1,3-dien-8-yne derivatives reacted efficiently at 80-110 °C with boryl(isopropoxy)silane or boryl(diethyamino)silane, which reacts as the synthetic equivalent of silylene, to afford 1-silacyclohepta-2,5-dienes (2,5-dihydro-1-silepines). Regiodivergent and chemo- and stereoselective functionalization of the seven-membered nonconjugated diene was achieved by hydroboration mediated by CsCO or an iridium catalyst.

Stereoinvertive C-C Bond Formation at the Boron-Bound Stereogenic Centers through Copper-Bipyridine-Catalyzed Intramolecular Coupling of α-Aminobenzylboronic Esters.

Enantiospecific intramolecular Suzuki-Miyaura-type coupling with α-(2-halobenzoylamino)benzylboronic esters to give 3-substituted isoindolinones is achieved by using copper catalysts with 2,2'-bipyridine-based achiral ligands. Enantioenriched α-aminobenzylboron reactants bearing a hydrogen atom at the boron-bound stereogenic carbons undergo stereoinvertive coupling in the presence of a 6-phenyl-2,2'-bipyridine ligand with high enantiospecificity. α-Aminobenzylboronates bearing fully substituted boron-bound stereogenic centers also gave the 3,3-disubstituted isoindolinones with stereospecific stereochemical inversion in the presence of simple 2,2'-bipyridine as a ligand.

Asymmetric Catalysis in Chiral Solvents: Chirality Transfer with Amplification of Homochirality through a Helical Macromolecular Scaffold.

Use of chiral solvents in asymmetric synthesis as a sole source of enantioselection remains largely unexplored in organic synthesis. We found that the use of a helical macromolecular catalyst of which helical chirality is dynamically formed in chiral solvents allowed several mechanistically different reactions to proceed with high enantioselectivity. In this system, the chirality of the solvent, such as limonene, induces a configurational imbalance to the helical macromolecular scaffold of the catalyst, and in turn to the reaction products through palladium-catalyzed asymmetric reactions including Suzuki-Miyaura cross-coupling (up to 98% ee), styrene hydrosilylation (up to 95% ee), and silaboration (up to 89% ee).

Boryl-Directed, Ir-Catalyzed C(sp)-H Borylation of Alkylboronic Acids Leading to Site-Selective Synthesis of Polyborylalkanes.

Pyrazolylaniline serves as a temporary directing group attached to the boron atom of alkylboronic acids in Ir-catalyzed C(sp)-H borylation. The reaction takes place at α-, β-, and γ-C-H bonds, giving polyborylated products including di-, tri-, tetra-, and even pentaborylalkanes. α-C-H borylation was generally found to be the preferred reaction of primary alkylboronic acid derivatives, whereas β- or γ-borylation also occurred if β- or γ-C-H bonds were located on the methyl group.

Telechelic Helical Poly(quinoxaline-2,3-diyl)s Containing a Structurally Defined, Circularly Polarized Luminescent Terquinoxaline Core: Synthesis by Core-Initiated Bidirectional Living Polymerization.

We have designed and synthesized divalent initiators that contain a fluorescent terquinoxaline unit with two palladium groups for the living polymerization of 1,2-diisocyanobenzenes. Using these divalent initiators, the bidirectional living polymerization of a monomer bearing ()-butoxymethyl side chains afforded telechelic helical poly(quinoxaline-2,3-diyl)s (PQXs), which consist of a terquinoxaline unit at the center of the polymer chain and chiral oligomeric blocks on both sides. The location of the core unit was confirmed by NMR spectroscopy and photoluminescence measurements.

Catalytic Generation of Rhodium Silylenoid for Alkene-Alkyne-Silylene [2 + 2 + 1] Cycloaddition.

An alkene-alkyne-silylene [2 + 2 + 1] cycloaddition takes place in the rhodium-catalyzed reaction of 1,6-enynes with borylsilanes bearing an alkoxy group on the silicon atoms, which react as synthetic equivalents of silylene. The reaction proceeds efficiently in 1,2-dichloroethane at 80-110 °C in the presence of a rhodium catalyst bearing bis(diphenylphosphino)methane (DPPM) as a ligand to afford 1-silacyclopent-2-enes in good to high yields.

Abnormal sergeants-and-soldiers effects of poly(quinoxaline-2,3-diyl)s enabling discrimination of one-carbon homologous n-alkanes through a highly sensitive solvent-dependent helix inversion.

Poly(quinoxaline-2,3-diyl)s bearing (S)-3-octyloxymethyl and n-propoxymethyl side chains show an abnormal sergeants-and-soldiers effect in n-alkane solvents, which allows the development of a series of PQXs that exhibit an extremely sensitive solvent-dependent helix inversion that permits the discrimination of n-alkane solvents that differ by a single methylene group (e.g. n-heptane and n-octane).

Enantiospecific Suzuki-Miyaura Coupling of Nonbenzylic α-(Acylamino)alkylboronic Acid Derivatives.

Suzuki-Miyaura coupling of nonbenzylic α-(acylamino)alkylboron compounds with aryl halides is established. A Pd/PCy Ph catalyst promotes the reaction efficiently at 145 °C. The reaction of enantioenriched α-(acylamino)alkylboron compounds affords chiral 1-arylalkylamides in high enantiospecificity and inversion of configuration.

Chirality-Amplifying, Dynamic Induction of Single-Handed Helix by Chiral Guests to Macromolecular Chiral Catalysts Bearing Boronyl Pendants as Receptor Sites.

Helical chirality of poly(quinoxaline-2,3-diyl)s bearing a boronyl pendant at the 5-position of the quinoxaline ring was induced by condensation with chiral guests such as a diol, diamine, and amino alcohol. Reversible induction of a single-handed helical structure was achieved by using less than an equimolar amount of chiral amino alcohols to the boronyl pendants. Majority-rule-effect-based chiral amplification on the polyquinoxaline main chain was demonstrated with chiral amino alcohols with low enantiomeric excess (ee).

Elucidating the Solvent Effect on the Switch of the Helicity of Poly(quinoxaline-2,3-diyl)s: A Conformational Analysis by Small-Angle Neutron Scattering.

Small-angle neutron scattering (SANS) was used to examine dilute solutions of a poly(quinoxaline-2,3-diyl) (PQX) with (R)-2-octyloxymethyl side chains in deuterated THF or a mixture of deuterated 1,1,2-TCE and THF (8/2, v/v), in which the PQX adopts pure P- and M-helical structures. The structures of the PQX that were obtained based on the SANS experiments in combination with theoretical calculations suggest that in THF, the chiral side chains of the P-helical PQX are extended, whereas in the 1,1,2-TCE/THF mixture, the side chains of the M-helical PQX are folded. Consequently, P-helical structures should be preferred in good solvents such as THF, which solvate the extended side chains, whereas M-helical structures should be preferred in poor solvents such as 1,1,2-TCE, wherein the side chains adopt shrunken conformations with maximized van der Waals interactions between the side chains.

Asymmetric Cycloisomerization of o-Alkenyl-N-Methylanilines to Indolines by Iridium-Catalyzed C(sp )-H Addition to Carbon-Carbon Double Bonds.

Highly enantioselective cycloisomerization of N-methylanilines, bearing o-alkenyl groups, into indolines is established. An iridium catalyst bearing a bidentate chiral diphosphine effectively promotes the intramolecular addition of the C(sp )-H bond across a carbon-carbon double bond in a highly enantioselective fashion. The reaction gives indolines bearing a quaternary stereogenic carbon center at the 3-position.

Chirality-Switchable 2,2'-Bipyridine Ligands Attached to Helical Poly(quinoxaline-2,3-diyl)s for Copper-Catalyzed Asymmetric Cyclopropanation of Alkenes.

Helical poly(quinoxaline-2,3-diyl)s copolymers consisting of a coordinating unit, which bears a varied achiral, substituted 2,2'-bipyridyl pendant, and a chiral unit bearing chiral side chains were synthesized and used as a ligand in copper-catalyzed asymmetric cyclopropanation of olefins with diazoacetates, giving up to 91:9 er with high chemical yield. The enantioselection relied on the helical structure of . A single afforded either of a pair of enantiomers with high enantioselectivity by switching its helical sense by changing the reaction solvent from pure toluene to a 3/1 mixture of toluene and 1,1,2-trichloroethane.

Synthesis and Catalytic Applications of a Triptycene-Based Monophosphine Ligand for Palladium-Mediated Organic Transformations.

1-Methoxy-8-(diphenylphosphino)triptycene (), featuring high structural rigidity and steric bulkiness around the phosphine functionality, was synthesized as a new chiral monophosphine ligand for transition metal-catalyzed reactions. In the presence of 5-10 mol ppm (i.e.

Poly(quinoxaline-2,3-diyl) as a Multifunctional Chiral Scaffold for Circularly Polarized Luminescent Materials: Color Tuning, Energy Transfer, and Switching of the CPL Handedness.

Random poly(quinoxaline-2,3-diyl) copolymers, containing achiral 5,8-diarylquinoxaline units and chiral units bearing ()-2-butoxymethyl groups, exhibited circularly polarized luminescence (CPL). The emission color was fully tunable by changing the aryl substituents on the 5,8-diarylquinoxaline units. An energy transfer from the quinoxaline main chain to the 5,8-diarylquinoxaline units was observed.

Utilization of a Trimethylsilyl Group as a Synthetic Equivalent of a Hydroxyl Group via Chemoselective C(sp)-H Borylation at the Methyl Group on Silicon.

A conversion of trimethylsilylalkanes into the corresponding alcohols is established based on an iridium-catalyzed, chemoselective C(sp)-H borylation of the methyl group on silicon. The (borylmethyl)silyl group formed by C(sp)-H borylation is treated with HO/NaOH, and the resulting (hydroxymethyl)silyl group is converted into a hydroxyl group by Brook rearrangement, followed by oxidation of the resulting methoxysilyl group under Tamao conditions. An alternative route proceeding through the formylsilyl group formed from a (hydroxymethyl)silyl group by Swern oxidation is also established.

Single-Handed Helical Poly(quinoxaline-2,3-diyl)s Bearing Achiral 4-Aminopyrid-3-yl Pendants as Highly Enantioselective, Reusable Chiral Nucleophilic Organocatalysts in the Steglich Reaction.

Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-aminopyrid-3-yl pendants were synthesized as new helical-polymer-based chiral nucleophilic organocatalysts. The obtained chiral nucleophilic polymer catalysts exhibited high catalytic activity, enantioselectivity, and reusability in asymmetric Steglich rearrangement of oxazolyl carbonate to C-carboxyazlactone. The polyquinoxaline-based, helically chiral DMAP catalyst mediated intramolecular acyl transfer selectively, by contrast with known small-molecule-based chiral organocatalysts, which also mediate intermolecular acyl transfers.

Regioselective Synthesis of o-Benzenediboronic Acids via Ir-Catalyzed o-C-H Borylation Directed by a Pyrazolylaniline-Modified Boronyl Group.

Ir-catalyzed ortho-directed C-H borylation of pyrazolylaniline (PZA)-modified arylboronic acids with bis(pinacolate)diboron afforded o-benzenediboronic acids in which two boronyl groups are differentially modified by pinacol (PIN) and PZA. By using this borylation after nondirected Ir-catalyzed C-H borylation, o-benzenediboronic acids are conveniently synthesized from unfunctionalized arenes. The differentially modified o-benzenediboronic acids undergo selective oxidation and Suzuki-Miyaura cross-coupling at the PZA-modified boronyl groups, affording o-functionalized arylboronic acids selectively.