Shinobu Takizawa

Efficient oxidative biaryl coupling reaction of phenol ether derivatives using hypervalent iodine(III) reagents

Abstract Oxidative biaryl coupling reaction of phenol ether derivatives with the hypervalent iodine reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA), in the presence of BF3·Et2O gave a variety of substituted biphenyl and binaphthyl compounds in high yields. Replacement of PIFA with a more practical polymer-supported hypervalent iodine reagent has also been achieved.

Enantioselective Synthesis of Isoindolines: An Organocatalyzed Domino Process Based On the aza-Morita-Baylis-Hillman Reaction**

The organocatalytic asymmetric domino process is a veryattractive method because of its ability to construct complexchiral molecules from readily available substrates under mildreaction conditions in two or more steps in a single operation.These reactions can save the time and the chemicals usuallyrequired for isolation or purification of the synthetic inter-mediates.Inaddition,noconcernformetalcontamination of the products is necessarybecause organocatalysts do not containtoxic or expensive metals. Examples oforganocatalytic asymmetric domino reac-tions mediated by chiral secondaryamines

Enantioselective Cyclization of 4-Alkenoic Acids via an Oxidative Allylic C–H Esterification

An enantioselective intramolecular oxidative cyclization of 4-alkenoic acids was developed. The reaction proceeded via a π-allyl Pd intermediate generated by an allylic C-H activation to give γ-lactone derivatives with moderate to good enantioselectivity. Spiro bis(isoxazoline) ligand, SPRIX, was indispensable for this asymmetric transformation.

Facile and Clean Oxidation of Alcohols in Water Using Hypervalent Iodine(III) Reagents

The facile and efficient oxidation of various alcohols such as benzylic alcohols, primary alcohols, secondary alcohols, and diols in water using the hypervalent iodine(III) reagent, iodosobenzene (PhI=O), with KBr is described. Electrospray ionization (ESI) mass spectrometric studies on the behavior of PhI=O-KBr in aqueous solution suggested that these reactions are induced by the formation of highly reactive iodine species [PhI(Br)nO –]. Further development to recyclable polymer-supported iodine(III) reagent extends the utility of this reaction to afford an environmentally benign method.

Enantioselective intramolecular oxidative aminocarbonylation of alkenylureas catalyzed by palladium-spiro bis(isoxazoline) complexes.

An enantioselective synthesis of tetrahydropyrrolo[1,2-c]pyrimidine-1,3-diones via a palladium-catalyzed intramolecular oxidative aminocarbonylation is described. The carbon-carbon double bond of alkenylurea substrates has been shown to react intramolecularly with a nitrogen nucleophile in the presence of a palladium catalyst under a carbon monoxide atmosphere. The use of a chiral spiro bis(isoxazoline) ligand (SPRIX) is essential to obtain the desired products in optically active forms. In comparison with the coordination ability of other known ligands, this peculiar character of SPRIX originates from two structural characteristics: low sigma-donor ability of the isoxazoline coordination site and rigidity of the spiro skeleton.

Total Synthesis of Chloropeptin II (Complestatin) and Chloropeptin I

The first total synthesis of chloropeptin II (1, complestatin) is disclosed. Key elements of the approach include the use of an intramolecular Larock indole synthesis for the initial macrocyclization, adopting conditions that permit utilization of a 2-bromoaniline, incorporating a terminal alkyne substituent (-SiEt(3)) that sterically dictates the indole cyclization regioselectivity, and benefiting from an aniline protecting group (-Ac) that enhances the atropdiastereoselectivity and diminishes the strained indole reactivity toward subsequent electrophilic reagents. Not only did this key reaction provide the fully functionalized right-hand ring system of 1 in superb conversion (89%) and good atropdiastereoselectivity (4:1 R:S), but it also represents the first reported example of what will prove to be a useful Larock macrocyclization strategy. Subsequent introduction of the left-hand ring system enlisting an aromatic nucleophilic substitution reaction for macrocyclization with biaryl ether formation completed the assemblage of the core bicyclic structure of 1. Intrinsic in the design of the approach and by virtue of the single-step acid-catalyzed conversion of chloropeptin II (1) to chloropeptin I (2), the route also provides a total synthesis of 2.

Hypervalent iodine(III) oxidation catalyzed by quaternary ammonium salt in micellar systems

Abstract Catalytic activation of iodosobenzene (PhIO) by cetyltrimethylammonium bromide (CTAB) allows sulfide oxidation reaction to occur in high yields under mild conditions in a variety of solvents. This PhIO activation may be due to the formation of micellar or reversed micellar systems.

Phosphine‐Catalyzed β,γ‐Umpolung Domino Reaction of Allenic Esters: Facile Synthesis of Tetrahydrobenzofuranones Bearing a Chiral Tetrasubstituted Stereogenic Carbon Center

An enantio-, diastereo-, regio-, and chemoselective phosphine-catalyzed β,γ-umpolung domino reaction of allenic esters with dienones has been developed for the first time. The designed sequence, involving oxy-Michael and Rauhut-Currier reactions, produced highly functionalized tetrahydrobenzofuranones, bearing a chiral tetrasubstituted stereogenic center, in up to 96 % ee.

Organocatalyzed formal [2 + 2] cycloaddition of ketimines with allenoates: facile access to azetidines with a chiral tetrasubstituted carbon stereogenic center.

An enantioselective organocatalyzed aza-MBH-type reaction of ketimines and allenoates has been developed. The present formal [2 + 2] cycloaddition produces highly functionalized azetidines with a chiral tetrasubstituted carbon stereogenic center in good to excellent yields and high enantioselectivities.

Chiral dinuclear vanadium(v) catalysts for oxidative coupling of 2-naphthols.

Preparation and structural analysis of chiral dinuclear vanadium(v) catalysts with high catalytic activity for the oxidative coupling of 2-naphthols are described.