Good Chemo Research Articles

A Fluorous Chiral Dirhodium(II) Complex as a Recyclable Asymmetric Catalyst

[reaction: see text] The chiral fluorous complex tetrakis-dirhodium(II)-(S)-N-(n-perfluorooctylsulfonyl)prolinate has been prepared and used as a catalyst in homogeneous or fluorous biphasic fashion. The catalyst displays good chemo- and enantioselectivity in intermolecular cyclopropanation and C-H bond activation reactions. The catalyst can be simply and thoroughly separated from the reaction mixture and is recyclable.

Stereochemistry of the Reaction of Si‐Phenyl Silenes with Butadienes: Elaboration of the Silacycloadducts to Provide a Novel Route to Substituted Lactones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Direct aldol reactions catalyzed by 1,1,3,3-tetramethylguanidine lactate without solvent

The ionic liquid, 1,1,3,3-tetramethylguanidine lactate ([TMG][Lac]), was used as a recyclable catalyst for direct aldol reactions at room temperature without any solvent. The results demonstrated that good chemo- and regio-selectivity could be achieved, and the ionic liquid can be easily recovered and recycled without considerable decrease of activity. The protocol is green and effective for producing β-hydroxyl ketones.

Stereoselective Intra- and Intermolecular [2+2] Photocycloaddition Reactions of 4-(2′-Aminoethyl)quinolones

The 4-(2'-aminoethyl)quinolones 6, 8 and 9 were prepared starting from 4-(2'-bromoethyl)quinolone (4) in two steps and overall yields of 56-93%. They underwent inter- and intramolecular [2+2] photocycloaddition reactions with an alkene to provide the cyclobutanes 1-3 in racemic form (61-89% yield). The photochemical reaction proceeded with very good chemo-, regio- and stereoselectivity. It was in one case (8b → 2b) also performed enantioselectively (93% ee).

Stereochemistry of the reaction of Si-phenyl silenes with butadienes: elaboration of the silacycloadducts to provide a novel route to substituted lactones.

Silenes generated through a silyl-modified Peterson olefination procedure can be trapped with a range of alkyl butadienes via a [4 + 2] cycloaddition pathway to afford silacycles accompanied by variable amounts of competing ene, [2 + 2] and silene dimer by-products. The silacycles are formed with good chemo- and stereo-selectivity and provide access to diols and lactones via a phenyl-triggered Fleming-Tamao oxidation.

Catalytic activity of palladium(II) complexes with tridentate nitrogen ligands in the hydrogenation of alkenes and alkynes

A series of palladium(II) complexes with the nitrogen ligands N-pyridin-2-yl- N′-pyridin-2-ylmethylene-hydrazine ( HL 1 ), and N, N-dimethyl- N′-pyridin-2-ylmethylene-ethane-1,2-diamine, ( L 2 ) have been synthesised and their catalytic activity in the hydrogenation of alkenes and alkynes in mild conditions ( P H 2 =1 atm, T=40 °C) has been studied. Ligand L 2 behaves as tridentate in the complexes Pd( L 2 )Cl 2 ( 4) and [Pd( L 2 )Cl](OTf) ( 5), whose catalytic activity is negligible in the hydrogenation of the tested substrates (styrene and phenylacetylene). The complexes Pd( L 1 )Cl ( 1) and Pd( L 1 )(OAc) ( 2) show a good catalytic activity towards styrene and phenylacetylene under homogeneous conditions. The high insolubility of the complex Pd 3( L 1 ) 2Cl 4 ( 3) prevents its use as catalyst in homogeneous hydrogenations; however, it has been employed in heterogeneous conditions, showing a very good chemo- and stereo-selectivity in the semi-hydrogenation of alkynes (phenylacetylene, diphenylacetylene and 4-octyne).

Chemo-, Regio-, and Stereoselective Cyclization of 1,3-Bis(trimethylsilyloxy)-1,3-butadienes with Functionalized Epoxides.

Very good chemo-, regio-, and stereoselectivities were obtained in the cyclization of 1,3-bis(trimethylsilyloxy)-1,3-butadienes—electroneutral equivalents of 1,3-dicarbonyl dianions—with functionalized epoxides [Eq. (1); R1, R2, R5=H, Me; R3=OMe, OEt, Ph, CH2OMe; R4=H, Me, Cl, Br, OBn, CO2Et, CH2CO2Et]. This reaction allows a convenient access to a variety of functionalized 2-alkylidenetetrahydrofurans which are of pharmacological relevance and of interest as intermediates in the synthesis of natural products (e.g. methyl nonactate).

Pig liver esterase (PLE)-mediated resolution of N-substituted 4-benzoyloxy-3-carbomethoxypiperidines: a convenient preparation of 4-hydroxy- and 4-benzoyloxy-3-carbomethoxypiperidines in enantiomerically pure form

Pig liver esterase (PLE) afforded smooth chemical resolution of racemic N-substituted 4-(benzoyloxy)-3-carbomethoxypiperidines. The enzyme showed good chemo- and enantioselective properties, thus allowing discrimination between the carbomethoxy and benzoate ester groups, the latter being more easily hydrolyzed. The proposed methodology also represents a practical means for the procurement of N-substituted 4-hydroxy-3-carbomethoxypiperidines in enantiomerically pure form.

The effects of process variables in the hydroformylation of methyl methacrylate with the in situ formed ( o-thiomethylphenyl)diphenylphosphine rhodium complex

The hydroformylation of methyl methacrylate (MMA) was studied with the in situ formed ( o-thiomethylphenyl)diphenylphosphine (SP) rhodium catalyst to establish the effect of the rhodium precursor, temperature, ligand-to-rhodium ratio, and hydrogen and carbon monoxide partial pressures on the activity and selectivity of the reaction. The performance of the SP modified reaction was compared to the performance of unmodified and triphenyl phosphine (PPh 3) modified reactions. In the case of the SP modified reaction, the rhodium precursor had a significant effect on the conversion, but only a minor effect on the selectivity. In contrast to the PPh 3 ligand, the regioselectivity of reaction did not change as the temperature and the total pressure were varied with a fixed [H 2]/[CO] ratio. Unfortunately, the deactivation of the catalyst was strong at elevated temperatures. The increase in hydrogen partial pressure increased the conversion of MMA but had no effect on the selectivity. A minimum carbon monoxide pressure was needed to achieve good chemo- and regioselectivities. The increase in catalyst concentration accelerated the rate of parallel hydrogenation.

Solid-State Photochemistry of o-Aroylbenzothioates: Absolute Asymmetric Phthalide Formation Involving 1,4-Aryl Migration

Solid-state photoreactions of S-(o-tolyl), S-phenyl, and S-(m-tolyl) 2-benzoylbenzothioates, which formed chiral crystals by spontaneous resolution, underwent an unprecedented intramolecular cyclization involving phenyl migration to afford optically active corresponding 3-phenyl-3-(arylthio)phthalide in good chemo- and enantioselectivities. Stereochemical assignment and substituent probe experiment of this photoreaction sequence led to a reliable conclusion that this reaction was rationalized on the basis of the aryl migration rather than the well-recognized radicalic mechanism. Furthermore, the chirality preservation in the crystals was demonstrated by means of the bisignated CD spectra, which allowed assignment of the origin of the specific CD band and the helicity of the chiral molecules.

Hydroformylation of some functionalized olefins catalyzed by rhodium(I) complexes with pydiphos and its P-oxide

The chiral optically active pyridylphosphines pydiphos ( 10) and its P-oxide ( 11) were tested as ligands in rhodium(I) complexes to form catalysts for the enantioselective hydroformylation of some functionalized olefins. These hydroformylation reactions provide in most cases good chemo- and regioselectivity, but unsatisfactory enantioselectivity. In the hydroformylation of styrene, vinyl acetate and phenyl vinyl ether, the Rh (I) complex containing the P-oxide 11 is remarkably more active than the catalyst formed with the pyridylphosphine analogue 10.

Hydroformylation of cinnamic acid derivatives catalysed by rhodium complexes

The hydroformylation of methyl cinnamate catalysed by various rhodium complexes affords the aldehyde 1a with good chemo- and regio-selectivity, while in the case of methyl p-chlorocinnamate the predominant reaction is the substrate hydrogenation. Higher yields of the desired aldehydes 1a and 1b are obtained by hydroformylation of the cinnamaldehyde and p-chlorocinnamaldehyde diethylacetal, respectively, under the same reaction conditions. These aldehyde products are valuable drug precursors.