Highly chemoselective hydrogenation with retention of the epoxide function using a heterogeneous Pd/C-ethylenediamine catalyst and THF

In general, palladium-carbon (Pd/C) catalyzed hydrogenation of epoxides affords the corresponding primary and secondary alcohols as a mixture. It has been found that the catalytic activity of a Pd/C -ethylenediamine complex catalyst [Pd/C(en)] in the hydrogenolysis of epoxide functions is drastically reduced. Herein we describe a mild and chemoselective method for the hydrogenation of olefin, nitro, and azide functions with retention of the epoxide function. The chemoselectivity was accomplished by using a combination of 5% Pd/C(en) and THF as solvent. A significant drop in the chemoselectivity of the hydrogenation is observed with 5% Pd/C(en) in MeOH. These results reinforce the utility of epoxides as important precursors of alcohols in synthetic chemistry.     

Cu-nanoparticles: a chemoselective catalyst for the aza-Michael reactions of N-alkyl- and N-arylpiperazines with acrylonitrile

A novel method for effecting the aza-Michael reactions of N-alkyl- and N-arylpiperazines with acrylonitrile using Cu-nanoparticles is described. The method features the use of 10 mol % Cu (14-17 nm) nanoparticles under mild reaction conditions to afford the addition products in good to excellent yields. The Cu-nanoparticles selectively catalysed the aza-Michael reaction of N-alkyl- and N-arylpiperazines in the presence of aromatic amino or aliphatic hydroxy groups.     

Pd/C-catalyzed chemoselective hydrogenation in the presence of a phenolic MPM protective group using pyridine as a catalyst poison

Employment of a Pd/C-pyridine combination as a catalyst is a very useful method for the selective removal (hydrogenolysis) of phenolic O-benzyl, N-Cbz and benzyl ester protective groups and for the selective hydrogenation of nitro and olefin functions of phenol derivatives protected with the MPM group. These discriminatory results are apparently attributable to the effect of pyridine. The MPM group could be extensively applied to chemoselective hydrogenation as a protective group for phenolic hydroxyl functions.     

Carbon dioxide hydrogenation to formic acid by using a heterogeneous gold catalyst

AUROlite, consisting of gold supported on titania (picture shows extrudates in a steel net cage), is a robust catalyst for the production of catalyst-free HCOOH/NEt(3) adducts from H(2), CO(2), and neat NEt(3). Pure HCOOH is freed from the adducts by amine exchange.     

A simple and efficient hydrogenation of benzyl alcohols to methylene compounds using triethylsilane and a palladium catalyst

Hydrogenolysis of benzyl alcohols using triethylsilane (Et₃SiH) and a catalytic amount of palladium(II) chloride (PdCl₂) is described. The reaction takes place under mild conditions affording high yields of the corresponding methylene compounds in short reaction times.     

N-Iodosuccinimide (NIS) as a mild and highly chemoselective catalyst for deprotection of tert-butyldimethylsilyl ethers

A variety of alcoholic TBDMS (t-butyldimethylsilyl) ethers are easily removed in excellent yields by treatment with a catalytic amount of N-iodosuccinimide (NIS, 5 mol %) in methanol. This method is able to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

Asymmetric hydrogenation of acetoacetic ester on a modified skeletal copper catalyst

Russian Chemical Bulletin -     

Highly chemoselective hydrogenation method using novel finely dispersed palladium catalyst on silk-fibroin: its preparation and activity

A palladium-fibroin complex (Pd/Fib) was prepared by soaking silk-fibroin in MeOH solution of Pd(OAc)₂ for 2 days (under Ar atmosphere)—4 days (under air). Pd(OAc)₂ was gradually absorbed by fibroin and the rapid reduction of fibroin conjugated Pd(OAc)₂ proceeded with MeOH as a reductant at room temperature to be the Pd(0) complex. Pd/Fib catalyzed chemoselective hydrogenation of acetylenes, olefins and azides in the presence of aromatic ketones and aldehydes, halides, N-Cbz protective groups and benzyl esters which are readily hydrogenated using Pd/C or Pd/C(en) as a catalyst.     

A highly chemoselective Boc protection of amines using sulfonic-acid-functionalized silica as an efficient heterogeneous recyclable catalyst

A facile and versatile method for the chemoselective Boc protection of amines has been developed by a treatment with (Boc)₂O in the presence of sulfonic-acid-functionalized silica as a catalyst. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic), aromatic, and heteroaromatic amines; primary and secondary amines; aminols, amino-esters; and sulfonamides. The catalyst works under heterogeneous conditions and can be recycled.     

Amberlyst-15: a mild, efficient and reusable heterogeneous catalyst for N-tert-butoxycarbonylation of amines

A mild and versatile method has been developed for the chemoselective N-tert-butoxycarbonylation of amines in the presence of Amberlyst-15 under solvent-free condition. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic) and aromatic amines.     

A green and chemoselective synthesis of coumarins via Pechmann condensation using recoverable heterogeneous catalyst (Au@pSiO2)

Nano Au@porous SiO₂ as a heterogeneous catalyst was prepared and characterized by Fourier transform infrared, X-ray powder diffraction, transmission electron microscopy, thermogravimetric analysis and inductively coupled plasma–atomic emission spectroscopy techniques and then used as an efficient catalyst in the condensation of various phenols with ethyl acetoacetate for the preparation of coumarin derivatives through the Pechmann reaction. The combined merits of chemoselective and solvent free reaction conditions and the recyclability of the nanostructured catalyst make the condensation a safe operation, with low pollution, rapid access to products and simple workup.     

An efficient chemoselective strategy for the preparation of (E)-cinnamic esters from cinnamaldehydes using heterogeneous catalyst and DDQ

An efficient chemoselective protocol is developed for the synthesis of (E)-cinnamic esters from substituted cinnamaldehydes or cinnamyl alcohols using a combination of DDQ and heterogeneous catalyst under microwave irradiation. The method showed remarkable selectivity for cinnamaldehydes over aliphatic and aromatic aldehydes, which is a novel finding. The results demonstrate that the developed protocol can be a useful synthetic tool for chemoselective esterification in total synthesis of complex organic compounds.     

One-pot synthesis of α-alkylated nitriles with carbonyl compounds through consecutive aldol reaction/hydrogenation using a hydrotalcite-supported palladium nanoparticle as a multifunctional heterogeneous catalyst

α-Alkylation of various nitriles with carbonyl compounds successfully proceeded using a hydrotalcite-supported palladium nanoparticle as a multifunctional catalyst. The alkylated nitriles were formed through aldol reaction at base sites on the hydrotalcite surface followed by hydrogenation by molecular hydrogen on the palladium nanoparticle.     

Cu-mediated chemoselective trifluoromethylation of benzyl bromides using shelf-stable electrophilic trifluoromethylating reagents

Copper-mediated chemoselective trifluoromethylation at the benzylic position by the use of shelf-stable electrophilic trifluoromethylating reagents 3 in good to high yields under mild conditions is described for the first time. The generality of this trifluoromethylation for a wide variety of benzyl bromides facilitates the rapid creation of structural diversity of medicinal candidates in drug discovery.     

Hydrogen bond catalyzed chemoselective N-tert-butoxycarbonylation of amines

A novel, chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butoxypyrocarbonate (Boc)₂O is described that relies on selective carbonyl activation by hydrogen bond formation. This mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor.     

An efficient heterogeneous catalytic system for chemoselective hydrogenation of unsaturated ketones in aqueous medium

A highly chemoselective and green heterogeneous catalytic system of immobilized Ru(II)–phenanthroline complexes on amino functionalised MCM-41 material for the chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols is demonstrated using water as a solvent. The XRD and FTIR spectra show the highly ordered hexagonal nature of the MCM-41, even after encapsulation of the ruthenium complex. The complex retains its configuration after anchoring, as was confirmed by FTIR and UV–Vis analysis. The detailed reaction parametric effect was studied for the hydrogenation of 3-methylpent-3-en-2-one to achieve complete conversion up to >99% chemoselectivity of 3-methylpent-3-en-2-ol. The anchored heterogeneous catalysts were recycled effectively and reused five times with marginal changes in activity and selectivity. The use of water as a solvent not only afforded high activity for the hydrogenation reaction compared to organic solvents, but also afforded a green process.     

Synthesis of novel serotonergics and other N-alkylamines using simple reductive amination using catalytic hydrogenation with Pd/C

Formation of N-alkylated α-methyltryptamine derivatives (2) was accomplished by simple reductive amination of amine (1) with ketones using catalytic hydrogenation conditions (3 atm H₂ and 10% Pd on carbon). This method was also applied to other primary and secondary amines using ketones and aldehydes.     

Aerobic alcohol oxidation using a PdCl2/N,N-dimethylacetamide catalyst system under mild conditions

A new and simple PdCl₂/DMA catalytic system for the alcohol oxidation has been developed using molecular oxygen as the sole oxidant under mild conditions. The catalytic system could be reused for three runs without significant loss of catalytic activity. A variety of active and non-active alcohols were oxidized to their corresponding carbonyl compounds in good to excellent yields. Gas-uptake kinetics for the catalytic system was also investigated. The ca. 1:1 molar ratio of O₂ uptake to product yield is observed, suggesting the in situ formation of H₂O₂.     

Unusual dimerization of N-protected bromomethylindoles/benzyl bromide with arylmetal halides: generation of indolylmethyl/benzyl radical

A detailed study on the interaction of N-protected bromomethylindoles with various types of aryl/alkyl Grignard is reported. Full experimental details on the mechanism of the unusual dimerization reaction are presented.