Michinori Suginome

Stereospecific Suzuki−Miyaura Coupling of Chiral α-(Acylamino)benzylboronic Esters with Inversion of Configuration

The first invertive B-alkyl Suzuki-Miyaura coupling has been achieved. The coupling of enantioenriched α-(acylamino)benzylboronic esters with aryl bromides and chlorides took place efficiently in toluene at 80 °C in the presence of Pd(dba)(2) (5 mol %), XPhos (10 mol %), K(2)CO(3) (3 equiv), and H(2)O (2 equiv). The reaction proceeded with inversion of configuration to give diarylmethanamine derivatives in high yields with high conservation of enantiomeric excesses.

High-Molecular-Weight Polyquinoxaline-Based Helically Chiral Phosphine (PQXphos) as Chirality-Switchable, Reusable, and Highly Enantioselective Monodentate Ligand in Catalytic Asymmetric Hydrosilylation of Styrenes

A polyquinoxaline-based helical polymer ligand bearing both helical-sense-determining chiral side chains and coordinating diarylphosphino side chains exhibits solvent-dependent formation of P- or M-helical structures, with which either the S- or R-hydrosilylation product was obtained with high (>93% enantiomeric excess) enantioselectivities.

Differentially Protected Diboron for Regioselective Diboration of Alkynes: Internal-Selective Cross-Coupling of 1-Alkene-1,2-diboronic Acid Derivatives

A differentially protected diboron bearing the naphthalene-1,8-diaminato group on one of the two boron atoms undergoes highly regioselective diboration with terminal alkynes in the presence of Pt or Ir catalysts, giving 1-alkene-1,2-diboronic acid derivatives in which the less reactive B(dan) group is located at the terminal position. The products undergo selective Suzuki-Miyaura coupling with aryl bromides at the internal boronyl group, leading to the formation of 2,2-disubstituted alkenylboronic acid derivatives.

Easily Attachable and Detachable ortho-Directing Agent for Arylboronic Acids in Ruthenium-Catalyzed Aromatic C−H Silylation

o-C-H silylation of arylboronic acids has been achieved using 2-pyrazol-5-ylaniline as an ortho-directing agent, which was temporarily attached to the boronyl group via Ru-catalyzed silylation with hydrosilanes. Condensation products of arylboronic acids with 2-pyrazol-5-ylaniline were prepared in situ and subjected to reaction with triorganosilanes in the presence of RuH(2)(CO)(PPh(3))(3) at 135 degrees C. Regioselective silylation at their ortho-positions proceeded in good yields for phenylboronic acids bearing para-substituents such as chloro, fluoro, methyl, methoxy, and trifluoromethyl groups. p-Methoxycarbonyl-substituted phenylboronic acid provided the corresponding silylated product in moderate yield. m-Tolyl- and 2-naphthylboronic acids underwent silylation selectively at the less sterically hindered ortho-positions. The silylated products were utilized in Suzuki-Miyaura coupling, followed either by iodination with ICl or by Tamao oxidation to furnish iodine- or hydroxy-substituted biaryls.

Differentially Protected Benzenediboronic Acids: Divalent Cross-Coupling Modules for the Efficient Synthesis of Boron-Substituted Oligoarenes

On the basis of the boron-masking strategy, new divalent cross-coupling modules have been designed for the efficient synthesis of boron-substituted oligoarenes. The modules, i.e., monoprotected o-, m-, and p-benzenediboronic acid derivatives, undergo highly selective Suzuki-Miyaura coupling with sp2 iodides, bromides, chlorides, and triflates, affording coupling products in which the protected boronyl groups are left intact.

Inversion or Retention? Effects of Acidic Additives on the Stereochemical Course in Enantiospecific Suzuki–Miyaura Coupling of α-(Acetylamino)benzylboronic Esters

The stereochemical course of the stereospecific Suzuki-Miyaura coupling of enantioenriched α-(acetylamino)benzylboronic esters with aryl bromides can be switched by the choice of acidic additives in the presence of a Pd/XPhos catalyst system. Highly enantiospecific, invertive C-C bond formation takes place with the use of phenol as an additive. In contrast, high enantiospecificity for retention of configuration is attained in the presence of Zr(Oi-Pr)(4)·i-PrOH as an additive.

Synthesis of B-Protected β-Styrylboronic Acids via Iridium-Catalyzed Hydroboration of Alkynes with 1,8-Naphthalenediaminatoborane Leading to Iterative Synthesis of Oligo(phenylenevinylene)s

Hydroboration of aromatic and aliphatic alkynes with 1,8-naphthalenediaminatoborane ((dan)BH) proceeded in the presence of [IrCl(cod)](2) complex with a DPPM or DPEphos ligand, affording alkenylboronic acids whose boronyl groups are masked by the diaminonaphthalene group. The masked alkenylboronic acids thus obtained from alkynes bearing halo-substituted aryl groups served as new coupling modules in an iterative Suzuki-Miyaura cross-coupling reaction for the synthesis of oligo(phenylenevinylene)s.

Regioselective Synthesis of 1,2-Dihydropyridines by Rhodium-Catalyzed Hydroboration of Pyridines

Pyridine undergoes addition of pinacolborane at 50 °C in the presence of a rhodium catalyst, giving N-boryl-1,2-dihydropyridine in a high yield. The selective 1,2-hydroboration also takes place in the reactions of substituted pyridines. In the reaction of 3-substituted pyridines, 3-substituted N-boryl-1,2-dihydropyridines are formed regioselectively.

Switch of Regioselectivity in Palladium-Catalyzed Silaboration of Terminal Alkynes by Ligand-Dependent Control of Reductive Elimination

The regioselectivity in the addition of silylboronic esters to terminal alkynes can be switched by the choice of phosphorus ligands on the palladium catalysts. The silaboration proceeds with normal regioselectivity in the presence of (eta(3)-C(3)H(5))Pd(PPh(3))Cl (1.0 mol %) to give 1-boryl-2-silyl-1-alkenes in high yields. In sharp contrast, selective formation of the inverse regioisomers, 2-boryl-1-silyl-1-alkenes, takes place when the reaction is carried out with a palladium catalyst bearing P(t-Bu)(2)(biphenyl-2-yl). A reaction mechanism for the change of regioselectivity that involves reversible insertion/beta-boryl elimination steps is proposed.

Regio- and stereoselective synthesis of boryl-substituted allylsilanes via transition metal-catalyzed silaboration

Abstract Regio- and stereo-controlled synthesis of boryl-substituted allylsilanes via transition metal-catalyzed additions of silylboranes to unsaturated organic compounds is described. Nickel-catalyzed reactions of (dimethylphenylsilyl)pinacolborane with 1,3-dienes, vinylcyclopropanes, and vinylcyclobutanes yielded 4-, 5-, and 6-boryl-substituted allylsilanes, respectively. Palladium-catalyzed addition of the silylborane to allenes took place at the more substituted CC bond to yield 2-borylallylsilane selectively. The 2-borylallylsilanes served as useful allylation reagents in Lewis acid-mediated reactions with acetals and aldehydes. In addition to the simple allylation reactions, a cascade reaction to form the trans -9-boryl-1,2-benzooxadecalin skeleton and a cyclization reaction to form cyclic alkenylboranes were achieved by the use of 2-borylallylsilanes as key reagents. Reactions of methylenecyclopropanes were catalyzed by palladium and platinum catalysts. The reaction course, however, depended upon the substrate structure and the catalyst employed. For instance, cycloalkylidenecyclopropanes yielded 2-cycloalkylidene-3-boryl-1-silylpropanes selectively in the presence of a palladium catalyst, while 3-cycloalkylidene-3-boryl-1-silylpropanes were obtained selectively in the corresponding platinum-catalyzed reactions.