Catalytic asymmetric dihydroxylation of olefins with recyclable osmate-exchanged chloroapatite catalyst

An osmate-exchanged chloroapatite (CAP-OsO₄) catalyst was prepared by an ion-exchange technique. CAP-OsO₄ efficiently catalyses asymmetric dihydroxylation of olefins including α,β-unsaturated esters and amides to afford the corresponding diols in high yields and enantioselectivities. The catalyst was reused for several cycles with consistent activity.     

Catalytic scaffolding ligands: an efficient strategy for directing reactions

The design and application of a scaffolding ligand that promotes branch and diastereoselective hydroformylation of terminal olefins as well as the regio- and diastereoselective hydroformylation of disubstituted olefins is reported. It is shown that the ligand covalently and reversibly bonds to the substrate, allowing for directed hydroformylation. As the substrate ligand interaction is dynamic, hydroformylations are catalytic in ligand and do not require any additional synthetic steps to add or remove the directing group. Using a catalytic quantity of a scaffolding ligand (20-25 mol %), excellent regioselectivity for disubstituted olefins (up to 98:2) and high branch selectivity (up to 88:12) for terminal olefins were obtained.     

Oxidations with IBX: benzyl halides to carbonyl compounds, and the one-pot conversion of olefins to 1,2-diketones

A variety of benzyl halides were converted to the corresponding aldehydes/ketones in respectable yields by IBX in DMSO at 65 °C. The bromohydrin reaction of olefins using NBS-H₂O in DMSO can be nicely adapted to IBX-mediated oxidation of benzyl halides in such a way that olefins are converted to the corresponding 1,2-diketones in good isolated yields in one-pot.     

Stereocontrolled photocyclization of 1,2-diketones: application of a 1,3-acetyl group transfer methodology to carbohydrates

Photolysis of 1-glycosyl-2,3-butanodione derivatives using visible light is a mild and selective procedure for the synthesis of chiral 1-hydroxy-1-methyl-5-oxaspiro[3.5]nonan-2-one carbohydrate derivatives. The results strongly suggest that stereocontrol of the cyclization is dependent on conformational and stereoelectronic factors. Further oxidative opening of the 1-hydroxy-1-methyl-2-cyclobutanone moiety affords new C-ketoside derivatives either in C- and O-glycoside series. This tandem two-step process could be considered to be a stereocontrolled 1,3-transference of an acetyl group, and it can be applied either to pyranose and furanose models.     

Catalytic coupling of C-H and C-I bonds using pyridine as a directing group

A method for the palladium-catalyzed arylation of pyridines and pyrazoles has been developed. Both aliphatic and aromatic C-H bonds may be functionalized using this method. A bromo substituent is tolerated on the aryl iodide coupling component. [reaction: see text]     

Regiospecific C-alkylation of uridine: a simple route to 6-alkyluridines

6-Alkyluridines were conveniently synthesized by lithiation and successive alkylation from 2′,3′-O-isopropylideneuridine with complete regioselectivity.     

A catalytic tethering strategy: simple aldehydes catalyze intermolecular alkene hydroaminations

Herein we describe a catalytic tethering strategy in which simple aldehyde precatalysts enable, through temporary intramolecularity, room-temperature intermolecular hydroamination reactivity and the synthesis of vicinal diamines. The catalyst allows the formation of a mixed aminal from an allylic amine and a hydroxylamine, resulting in a facile intramolecular hydroamination event. The promising enantioselectivities obtained with a chiral aldehyde also highlight the potential of this catalytic tethering approach in asymmetric catalysis and demonstrate that efficient enantioinduction relying only on temporary intramolecularity is possible.     

Nitrile-promoted Rh-catalyzed intermolecular hydroacylation of olefins with salicylaldehyde

Rh-catalyzed intermolecular hydroacylation between salicylaldehyde and alkenylnitriles proceeded at room temperature to preferentially give normal-hydroacylated products. Addition of CH3CN and NaOAc accelerated the Rh-catalyzed hydroacylation of monoolefins to exclusively produce the normal-hydroacylated products under mild reaction conditions. Plausible mechanisms for the regioselections are also described.     

Solvent-free hydroalkylation of olefins with 1,3-diketones catalyzed by phosphotungstic acid

An efficient and convenient method for the direct hydroalkylation of styrene and norborene with 1,3-diketones has been developed by using 12-phosphotungstic acid as an eco-friendly, and air- and moisture-tolerable catalyst. Reactions proceeded without any solvent, providing a clean access to alkylated 1,3-diketones.     

Reaction of Z isomers of alkylaromatic 1,2-hydroxylamino oximes with 1,2-diketones

The reactions of Z isomers of alkylaromatic 1,2-hydroxylamino oximes containing the hydroxylamino group at the primary or secondary carbon atom with diacetyl afford 6-acetyl-5,6-dihydro-4H-1,2,5-oxadiazines. The reactions of these compounds with alkylaromatic 1,2-diketones produce N-substituted α-aroylnitrones or 6-aroyl-5,6-dihydro-4H-1,2,5-oxadiazines or, alternatively, their tautomeric mixtures. Dedicated to the memory of Academician V. A. Koptyug on the occasion of the 75th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1008–1013, June, 2006.     

Iron-promoted C-C bond cleavage of 1,3-diketones: a route to 1,2-diketones under mild reaction conditions

A conceptual method for the preparation of 1,2-diketones is reported. The selective C-C bond cleavage of 1,3-diketones affords the 1,2-diketones in high yields under mild reaction conditions in air by the use of FeCl(3) as the catalyst and tert-butyl nitrite (TBN) as the oxidant without the use of solvent. The possible reaction mechanism is discussed. This protocol provides an expeditious route to the useful 1,2-diketones.     

Catalytic allylic oxidation with a recyclable, fluorous seleninic acid

In conjunction with iodoxybenzene as reoxidant perfluorooctylseleninic acid catalyzes the allylic oxidation of alkenes to enones in trifluoromethylbenzene at reflux in moderate to good yield. After a reductive workup with sodium metabisulfite, the catalyst is recovered by fluorous extraction in the form of bis(perfluorooctyl) diselenide, which, itself, serves as a convenient catalyst precursor. [reaction: see text]     

Rhodium(II) catalyzed intermolecular double C-alkylation: a method for the synthesis of tetraindoles and indolophanes

Double C-alkylation of cyclic diazoamides or bis-diazoamides with indoles or bis-indoles has been achieved to synthesize tetraindole derivatives using rhodium(II) acetate as a catalyst under mild reaction conditions with complete regioselectivity. The intermolecular double C-alkylation reaction strategy was successfully applied to synthesize indolophanes in moderate yield with excellent regiocontrol. The structure and stereochemistry of macrocycles were unequivocally confirmed with the help of single-crystal X-ray structure analyses.