▼Intramolecular Dehydrative Condensation of Dicarboxylic Acids with Bronsted Base-Assisted Boronic Acid Catalysts
Aust. J. Chem. 2011, 64, 1458-1465.
Bifunctional Bronsted base-assisted boronic acid catalysts, arylboronic acids bearing two sterically bulky (N,Ndialkylamino) methyl groups at the 2,6-positions, exhibit remarkable activities for the dehydrative intramolecular condensation of dicarboxylic acids. The steric bulkiness of the (N,N-dialkylamino)methyl groups of 1, which prevents the formation of less active species such as the N-B chelated species and triarylboroxines 3, is crucial for the high catalytic activity. This is the first successful method for the catalytic dehydrative self-condensation of di- and tetracarboxylic acids.
▼Enantioselective Diels-Alder Reactions with Anomalous endo/exo Selectivities Using Conformationally Flexible Chiral Supramolecular Catalysts
Angew. Chem. Int. Ed. 2011, 50(51), 12189-12192.
Swapped selectivities: The use of tailor-made catalysts results in anomalous endo/exo selectivities and high enantioselectivities in the Diels-Alder reactions of cyclopentadiene with different acroleins (see scheme). These supramolecular catalysts are prepared in situ from chiral diols, arylboronic acid, and tris(pentafluorophenyl)borane, and can discriminate the re/si face of the dienophile as well as the endo/exo approach of the diene.
▼Desymmetrization of meso-Glycerol Derivatives Induced by L-Histidine-Derived Acylation Catalysts
Adv. Synth. & Catal. 2011, 353(11-12), 1938-1942.
(Article first published online: 10 AUG 2011)
The desymmetrization of meso-glycerol derivatives bearing a 3-pyrroline-1-carbonyl (Pyroc) directing group is demonstrated through an enantioselective acylation reaction promoted by L-histidine-derived bifunctional catalysts. The desired monoacylated products are obtained in good yields (up to 74%) with high enantioselectivities (up to 99% ee).
▼Catalytic Enantioselective Alkyl and Aryl Addition to Aldehydes and Ketones with Organozinc Reagents Derived from Alkyl Grignard Reagents or Arylboronic Acids
Catal. Sci. Technol. 2011, 1, 1149-1158.
(Article first published online: 10 AUG 2011)
A highly practical, catalytic enantioselective alkyl and aryl addition to aldehydes and ketones with organozinc reagents, which were prepared in situ from commercially available Grignard reagents or arylboronic acids, was developed. A chiral phosphoramide ligand was essential for promoting the addition reactions in high yields with high enantioselectivities.
▼Chiral Lewis Base-Assisted Bronsted Acid (LBBA)-Catalyzed Enantioselective Cyclization of 2-Geranylphenols
Org. Lett. 2011, 13, 3130-3133.
Chiral Lewis base-assisted Bronsted acids (Chiral LBBAs) have been designed as new organocatalysts for biomimetic enantioselective cyclization. A salt of a chiral phosphonous acid diester with FSO3H catalyzes the enantioselective cyclization of 2-geranylphenols to give the desired trans-fused cyclized products with high diastereo- and enantioselectivities (up to 98:2 dr and 93% ee).
▼In Situ Generated (Hypo)Iodite Catalysts for the Direct alpha-Oxyacylation of Carbonyl Compounds with Carboxylic Acids
Angew. Chem. Int. Ed. 2011, 50(23), 5331-5334.
It's the iodine: The intra- and intermolecular title reaction is catalyzed by an in situ generated ammonium (hypo)iodite species. Either H2O2 or tert-butyl hydroperoxide (TBHP) can be used as an environmentally benign oxidant and a wide range of substrates react to give the corresponding alpha-acyloxycarbonyl compounds in good to excellent yields.
▼Enantioselective Friedel-Crafts Aminoalkylation Catalyzed by Chiral Ammonium 1,1'-Binaphthyl-2,2'-disulfonates
Synlett 2011, 1247-1250.
A catalytic enantioselective Friedel-Crafts aminoalkylation between aromatic aldimines and N-benzylpyrrole with the use of a homogeneous chiral ammonium salt, (R)-BINSA-N,N-dimethylbutylamine, as a dynamic Bronsted acid-Bronsted base catalyst, is reported. Unlike the results with conventional catalysts, remarkably high reactivity was established at -78 C within 30 minutes, and the corresponding aryl(1H-pyrrol-2-yl)methanamines were obtained with good to high enantioselectivities.
▼Commercially available neat organozincs as highly reactive reagents for catalytic enantioselective addition to ketones and aldehydes under solvent free conditions
Tetrahedron 2011, 67, 4417-4424.
Neat Et2Zn, Ph2Zn, and highly concentrated Me2Zn are highly reactive organozinc reagents, which are commercially available in bulk quantities. We here report a catalytic enantioselective Et2Zn, Ph2Zn, and Me2Zn addition to ketones and aldehydes under solvent free or highly concentrated conditions without Ti(Oi-Pr)4 as a conventional activator of organozinc reagents. The desired optically active tertiary and secondary alcohols were obtained in good yield with high enantioselectivity when compared to the conventional solvent-use conditions. From the viewpoint of ecological and environmental reasons in green chemistry, this catalysis would be practical for not only academic but also industrial use.
▼Brønsted Base-Assisted Boronic Acid Catalysis for the Dehydrative Intramolecular Condensation of Dicarboxylic Acids
Org. Lett. 2011, 13, 892-895.
Brønsted base-assisted boronic acid catalysis for the dehydrative self-condensation of carboxylic acids is described. Arylboronic acid bearing bulky (N,N-dialkylamino)methyl groups at the 2,6-positions can catalyze the intramolecular dehydrative condensation of di- and tetracarboxylic acids. This is the first successful method for the catalytic dehydrative self-condensation of carboxylic acids.
▼In situ-generated chiral quaternary ammonium (hypo)iodite catalysis for enantioselective oxidative cyclizations
Chimica Oggi-Chemistry Today 2011, 29(1), 18-21.
Very recently, we developed the first enantioselective oxidative cycloetherification of ketophenols to 2-acyl- 2,3-dihydrobenzofuran derivatives catalysed by in situgenerated chiral quaternary ammonium (hypo)iodite with hydrogen peroxide or tert-butyl hydroperoxide (TBHP) as an environmentally benign ideal oxidant. The optically active 2-acyl 2,3-dihydrobenzofuran skeleton is a key structure in several medicinally and biologically active compounds.
▼2-Iodoxybenzenesulfonic Acid (IBS) Catalyzed Oxidation of Alcohols
Aldrichmica Acta 2010, 43(3), 83-91.
2. Hypervalent Iodine Catalysts for Alcohol Oxidation
3. 2-Iodoxybenzenesulfonic Acid (IBS)
3.1. Related Hypervalent Iodine Reagents
3.1.1. HMBI and λ3-Iodane Derivatives
3.1.2. IBS and λ5-Iodane Derivatives
3.2. Discovery of IBS as a Catalyst for Alcohol Oxidation with OxoneR
3.3. Large-Scale Oxidations
3.4. Application to the Oxidative Rearrangement of Tertiary Allylic Alcohols
3.5. Theoretical Calculations and Reaction Mechanism
6. References and Notes
▼Lanthanum(III) Isopropoxide Catalyzed Chemoselective Transesterification of Dimethyl Carbonate and Methyl Carbamates
Org. Lett. 2011, 13(3), 430-433.
A practical transesterification of less reactive dimethyl carbonate and much less reactive methyl carbamates with primary (1°), secondary (2°), and tertiary (3°) alcohols was established with the use of a lanthanum(III) complex, which was prepared in situ from lanthanum(III) isopropoxide (3 mol %) and 2-(2-methoxyethoxy)ethanol (6 mol %). In particular, corresponding carbonates and carbamates obtained were of synthetic utility from the viewpoint of the selective protection and/or deprotection of 1°-, 2°-, and 3°-alcohols.
▼Ligand-Assisted Rate Acceleration in Lanthanum(III) Isopropoxide Catalyzed Transesterification of Carboxylic Esters
Org. Lett. 2011, 13(3), 426-429.
The transesterification of an equimolar mixture of carboxylic esters and primary (1°), secondary (2°), and tertiary (3°) alcohols in hydrocarbon solvents was promoted with high efficiency by a lanthanum(III) complex, which was prepared in situ from lanthanum(III) isopropoxide (1 mol %) and 2-(2-methoxyethoxy)ethanol (2 mol %). The present La(III) catalyst was highly effective for the chemoselective transesterification in the presence of competitive 1°- and 2°-amines. Remarkably, esters were obtained in good to excellent yields as colorless materials without an inconvenient workup procedure.