Dicationic ((−)-sparteine)palladium-catalyzed enantioselective aldol reaction of aldehydes with 1-phenyl-1-trimethylsilyloxyethene, proceeding via a palladium enolate

A dicationic ((−)-sparteine)palladium complex underwent a superior catalytic enantioselective aldol reaction of aldehydes with 1-phenyl-1-trimethylsilyloxyethene performing satisfactorily, starting with ((−)-sparteine)PdCl₂ and AgSbF₆ as catalyst precursors (1 mol % loading) in the presence of 3 Å molecular sieves over the reaction.     

Planar chiral cyclic ether: asymmetric resolution and chirality transformation

Remarkably stable planar chirality was found in a nine-membered diallylic cyclic ether. Enantiomerically enriched ether was prepared by a kinetic resolution of a racemic one, which is valuable as a novel type of chiral building block.     

Diphenylboron perchlorate as an efficient catalyst for self- and cross-condensation reactions of aldehydes having α-active hydrogens

Diphenylboron perchlorate very smoothly catalyzed self- and cross-condensation reactions of aldehydes at rt in nitroethane. The new catalyst provided novel behaviors owing to the characteristics of possessing a covalency in the boronoxygen bond, compared with ionic perchlorates.     

Three-component photopolymer based on a novel mechanism: acid-catalyzed polymerization and decoupling of crosslinks

Three-component photopolymers comprising a photoacid generator, a bifunctional vinyl ether monomer and an aqueous base-soluble polymer as matrix were developed. These photopolymers exhibit either positive- or negative-working character, depending on the prebake temperature and the concentration of the photoacid generator. When the prebake temperature is high, the photo-polymer film is made insoluble in aqueous base and organic solvents by the formation of crosslinks. However, on exposure to light, the crosslinks are decoupled by the photogenerated acid and the photopolymer layer becomes again soluble in aqueous base, resulting in a positive-working character. When the concentration of the photoacid generator is low enough, the photopolymer has a negative-working character due to the cationic polymerization of vinyl ethers. The mechanism of the photochemical reaction of the photopolymers was investigated to elucidate the complicated behavior.     

Platinum(II) complex-catalyzed enantioselective aldol reaction with ketene silyl acetals in DMF at room temperature

[{(R)-binap}Pt(μ-OH)]₂2X is a weak Lewis acid, which can catalyze the enantioselective aldol reaction of aldehydes with ketene silyl acetals in DMF at room temperature. The platinum(II) complex-catalyzed the enantioselective aldol reaction of aldehydes with 1-methoxy-2-methyl-(1-trimethylsilyloxy)propene gave the corresponding aldols in high yields with enantioselectivity up to 92%. With 5 mol % loading of the complexes, the enantioselective aldol reaction of aldehydes with 1-benzyloxy-1-(trimethylsilyloxy)propene smoothly proceeded in DMF containing 10% HMPA as to predominantly give anti-propionates with enantioselectivity up to 89%, irrespective of the silyl nucleophile geometry.     

Intramolecular titanium-promoted deoxygenative cyclization to 9-substituted-1,2,3,4-tetrahydrofluorene skeleton

The Mukaiyama aldol reaction of 2-aryl-1-cyclohexene-1-carboxaldehydes with phenyl trimethylsilyl ketene acetal unexpectedly resulted in the formation of 9-substituted-1,2,3,4-tetrahydrofluorene derivatives via a novel intramolecular titanium-promoted deoxygenative cyclization. By successive treatment of the corresponding allyl alcohols with n-butyllithium and titanium tetrachloride, the cyclization products were obtained in good yields.     

Lewis acid-aldehyde-solvent interactions. A computational approach for determining the critical amount of THF molecules necessary for achieving a high enantioselection in chiral oxazaborolidinone-promoted asymmetric aldol reactions

The effect of THF as a solvent on the enantioselectivity of oxazaborolidinone-promoted asymmetric aldol reactions of aldehydes with silylketene acetals was investigated. The use of 4-5 M equiv of THF, relative to the chiral borane, was required to achieve a high enantioselectivity. A solvent-modeling study, based on ab initio calculations of intermolecular interactions, revealed the existence of an extended hydrogen bonding network in the resulting assembly, which was composed of THF molecules, the aldehyde, and the oxazaborolidinone. The model rationally provides a spatially suitable active site for controlling the stereochemical outcome of the reaction.     

The first N,N′-ditosyl-substituted cyclic boron cation, stabilized by neighboring-group participation by two sulfonyl groups, and the alternative, stabilized by polar solvents

When 2-bromo-1,3-ditosyl-1,3,2-diazaborolidine was treated with AgSbF₆, a novel cyclic boron cation was formed in CD₂Cl₂, the ¹¹B NMR chemical shift of which appeared at 8.7 ppm. Ab initio calculations were consistent with the cationic boron center being stabilized by neighboring-group participation of the two sulfonyl functions. The reaction in CD₃NO₂ resulted in an alternate formation of a cyclic boron cation species (16.2 ppm), stabilized by coordination to the basic solvents.     

Preparation and characterization of diphenylboron cation in solution

The electrophilic abstraction of chloride ion by SbCl₅ from diphenylchloroborane in CD₃NO₂ resulted in a transient species of which ¹¹B NMR chemical shift appeared at 20 ppm. This was indicative of diphenylboron cation, stabilized with electron donor O-atom of two nitromethane molecules. The experimental ¹¹B chemical shift for the solvated diphenylboron cation is in good agreement with that calculated by GIAO-HF/6-311+G(2d,p)//B3LYP/6-31+G(d).     

Iridium-catalyzed double incorporation reaction of N-benzylmaleimide to styrene via ortho-C-H bond activation, initiated by precoordination of the double bond of styrene to iridium

Reaction of styrene with N-benzylmaleimide in the presence of [IrCl(cod)]₂ (5 mol %) and bpy (10 mol %) in an autoclave (1 MPa of Ar) at 150 °C for 18 h stereoselectively led to the formation of a new cyclic product. The structure of the product suggests that a novel iridium-catalyzed double incorporation reaction takes place via a metallacyclopentane formed after ortho-C-H activation.