Zirconium-catalyzed chemoselective methylalumination of ethers, amines, and sulfides bearing two terminal alkenyl groups

Chemoselectivity in the methylalumination reaction of unsymmetrical ethers, amines, and sulfides bearing two different terminal alkenyl groups, a 13-tetradecenyl group and an allyl, 4-pentenyl or 6-heptenyl group was examined. The methylalumination of the allyl derivatives proceeded with complete chemoselectivity to afford only the 13-tetradecenyl-monomethylated products. In the methylalumination reactions of the 4-pentenyl and the 6-heptenyl derivatives, in addition to the 13-tetradecenyl-monomethylated products, and dimethylated products were also obtained. However, as in the case of the allyl derivatives, monomethylation to the shorter 4-pentenyl or 6-heptenyl group was not observed, except in the case of 6-heptenyl 13-tetradecenyl amine. The unique selectivity was rationalized upon how readily the intramolecular ligand exchange reaction between intermediate zirconocenium-alkene and zirconocenium-heteroatom complexes could occur.     

Palladium nanoparticles-catalyzed chemoselective hydrogenations, a recyclable system in water

Chemoselective hydrogenation of double bonds in the presence of various functional groups occurred in high yields using water or toluene as solvent, and Pd nanoparticles as catalyst. Up to nine recyclings were achieved in water without decrease of the catalyst activity.     

Recent advances in chemoselective acylation of amines

N-chemoselective acylation of amines in the presence of competing nucleophiles, like alcohols and thiols, is by no means a simple achievement in organic synthesis and even more difficulties arise when distinctions between primary, secondary, and aromatic amines need to be made. The present digest will review some recent achievements in this field, ranging from transamidation reactions to carboxylic acid derivatives transacylations. In addition, more creative strategies, involving chemoenzymatic reactions and metal-catalyzed acylations and carbonylations, will be discussed in order to furnish a concise view of the state-of-the-art approaches to this synthetic challenge.     

Organocatalytic synthesis of amides from nitriles via the Ritter reaction

A simple, inexpensive, environmentally friendly, and efficient route for the synthesis of a wide variety of amides in high yields via the Ritter reaction of alcohols with nitriles has been demonstrated. Pentafluorophenyl ammonium triflate (PFPAT) is used as an organocatalyst and is air-stable, cost-effective, easy to handle, and easily removed from the reaction mixtures.     

Synthesis of non-symmetrical alkynylpyridines by chemoselective Sonogashira cross-coupling reactions

4-Bromo-2,3,5-trichloro-6-iodopyridine was studied as a new substrate in chemoselective Sonogashira reactions. This approach provides an efficient access to non-symmetrical mono-, di-, tri- and pentaalkynylated pyridines in good yields. Selected pentaalkynylated pyridines were studied with regard to their UV/Vis- and emission properties showing moderate to high fluorescence quantum yields.     

Organocatalytic asymmetric synthesis of quinine and quinidine

Quinine and quinidine were synthesized by a highly enantio- and stereoselective approach starting from a proline-catalyzed asymmetric cycloaldolization of benzyl bis(2-formylethyl)carbamate which gave a 70:30 mixture of (3R,4R)-N-Cbz-3-hydroxymethyl-4-hydroxypiperidine (96% ee) and its 4S-epimer (92% ee) in 94% yield after in situ NaBH₄ reduction.     

Graphene oxide (GO)-catalyzed chemoselective thioacetalization of aldehydes under solvent-free conditions

An efficient method for the synthesis of open chain, cyclic, and unsymmetrical dithioacetals from aryl/hetero-aryl/aliphatic aldehydes is described. The reaction is performed using graphene oxide (GO) as the catalyst under solvent-free and aerobic conditions. High chemoselectivity is observed in the reaction as aryl/alkyl ketones do not give thioketals under the condition.     

Synthesis of hexopyranosyl acetates and 2,3-disubstituted tetrahydropyrans via chemoselective hydrogenation of hex-2-enopyranosyl acetates

A simple and easy method for chemoselective synthesis of hexopyranosyl acetates and 2,3-disubstituted tetrahydropyrans from hex-2-enopyranosyl acetates was demonstrated. The former was achieved by hydrogenation catalyzed by Rh/Al₂O₃ in EtOAc/toluene solvent at 0 °C, while the latter was carried out using Pd/C in EtOH/AcOH at 25 °C.     

Ferrous methanesulfonate as an efficient and recyclable catalyst for chemoselective synthesis of 1,1-diacetate from aldehydes

Ferrous methanesulfonate catalysing the conversion of aromatic,heteroaromatic,unsaturated,and aliphatic aldehydes to 1,1- diacetates at room temperature under solvent-free condition has been developed.The catalytic activity of seventeen metal methanesulfonates was compared under the same condition,ferrous methanesufonate proved to be the best.It can be easily recovered and reused for several times without distinct deterioration in catalytic activity.During the competitive protection between a ketone and ...     

Organocatalytic enantioselective tandem Michael addition-oxidation of 3-substituted oxindoles with 1,4-benzoquinone

By employing a chiral bifunctional thiourea-tertiary amine as catalyst, enantioselective tandem Michael addition-oxidation of 3-monosubstituted oxindoles with 1,4-benzoquinones were realized. The reactions afforded a wide range of 3,3-disubstituted oxindoles with moderate to good yields (up to 87%) in moderate to good enantioselectivities (up to 96%).     

Self-modulated highly chemoselective direct-reductive-amination (DRA) of benzaldehydes straightforward to N-monosubstituted benzylamine hydrochlorides

An unprecedented efficient and chemoselective DRA of benzaldehydes and primary amines was developed to directly yield N-monosubstituted benzylamine hydrochlorides as single products in practically quantitative yields. The method was characterized by simply adding a few milliliters of CHCl₃ in the conventional Pd-C catalytic hydrogenation system at atmospheric pressure and room temperature. A self-modulated system and a four-stage cyclic pathway were proposed.     

A recyclable fluorous thiourea organocatalyst for the chemoselective oxidation of sulfides

As a kind of organocatalyst, 1-[4-(perfluorooctyl)phenyl]-3-phenylthiourea was employed to the chemoselective oxidation of sulfides in the presence of 30% H₂O₂. A variety of diaryl, dialkyl, alkyl aryl sulfides could be oxidized to sulfoxide under the mild condition. The catalyst could be easily recovered by fluorous solid-phase extraction for reuse.     

Highly chemoselective synthesis of aryl allylic sulfoxides through calcium hypobromite oxidation of aryl allylic sulfides

A highly chemoselective oxidation of widely substituted aryl allylic sulfides, prepared by allylation of arylthioethers with KF-Celite, to the corresponding aryl allylic sulfoxide was achieved by employing calcium hypobromite. Neither over-oxidation to sulfones nor halogenation of the aromatic rings was observed. The protocol may be successfully applied for the oxidation of substituted allylic systems (i.e., 2-haloallyl) that per se could interact with the oxidizing agent.     

Syntheses of methylenolactocin and nephrosterinic acid via diastereoselective acylation and chemoselective reduction-lactonization

The syntheses of methylenolactocin, nephrosterinic acid and their derivatives can be achieved by using the efficient diastereoselective acylation of dimethyl itaconate-anthracene adduct followed by tandem chemoselective reduction-lactonization.     

A highly regio- and chemoselective synthesis of vicinal bromohydrins by ring opening of terminal epoxides with dibromoborane-dimethyl sulfide

Dibromoborane-dimethyl sulfide (BHBr₂-SMe₂) displays high degrees of chemo- and regioselectivity during the brominative cleavage of the epoxy group into vicinal bromohydrins in the presence of alkene, alkyne, allene, ether, acetal and acetonide, besides its hydroborating ability. Several reducible functional groups, such as chloride, aldehyde, ketone, azide, ester, nitrile and tert-amino ester, have been successfully accommodated during the epoxide opening process.     

Copper nitrate/acetic acid as an efficient synergistic catalytic system for the chemoselective tetrahydropyranylation of alcohols and phenols

Abstract  Tetrahydropyranylation of alcohols and phenols was accomplished successfully using copper nitrate and acetic acid as a synergistic catalyst at room temperature under solvent-free condition. Compared with other synergistic catalytic systems, copper nitrate/acetic acid proved to be the most efficient. Both alcohols (primary, secondary, tertiary, benzylic, cyclic, allyl, cinnamyl, and furyl) and phenols reacted smoothly in high yields. Graphical abstract        

Organocatalytic asymmetric 1,4-addition of organoboronic acids to γ-hydroxy α,β-unsaturated aldehyde: facile synthesis of chiral β-substituted γ-lactones

Catalytic asymmetric 1,4-addition of arylvinyl- and arylboronic acids to a γ-hydroxy α,β-unsaturated aldehyde, which affords β-substituted γ-lactols, has been established using a diarylprolinol silyl ether as an organocatalyst. The β-substituted γ-lactols have been obtained in good yields and with up to 91% ee, which lead to chiral β-substituted γ-lactones followed by oxidation.     

Organocatalytic intermolecular [2+2] cycloaddition of norbornadienes by a stable organic radical compound

An organocatalytic [2+2] cycloaddition reaction of norbornadienes (NBDs) using catalytic amount of TEMPO was reported. Single crystal X-ray diffraction of the product revealed its detailed multicyclic structure containing a 4-membered ring, formed in intermolecular reaction. Addition of AIBN to the current catalytic system improved the product yield. Quantitative reaction of the NBD and TEMPO gave a 2:2 adduct of NBD and TEMPO, which was confirmed by HR-MS. This catalytic [2+2] addition of NBDs has great advantage in selective intermolecular coupling in comparison with [2+2] photocycloaddition.     

EDC-mediated condensations of 1-chloro-5-hydrazino-9,10-anthracenedione, 1-hydrazino-9,10-anthracenedione, and the corresponding anthrapyrazoles

The EDC-mediated condensation of 1-chloro-5-hydrazino-9,10-anthracenedione afforded an N-1 acyl anthrapyrazole instead of the expected hydrazide. The regiochemistry of the N-acyl substituent was assigned on the basis of an extensive set of NMR experiments, and identification of this isomer suggests a reaction sequence based on initial acylation and subsequent cyclization. In contrast, the parallel reaction of 1-hydrazino-9,10-anthracenedione proceeded to afford the expected hydrazide.