Transformations of formaldehyde and glycolaldehyde during the hydroformylation of formaldehyde in the presence of rhodium catalysts

Hydroformylation of formaldehyde to give glycolaldehyde (GA) in the presence of RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, or the RhCl₃ + PPh₃ system inN,N-dimethylacetamide was studied. The hydroformylation is accompanied by the Cannizzaro-Tishchenko reaction, condensation of CH₂O with GA to give C₃-C₁₆ polyoxyaldehydes (POA), and dimerization of GA. The formation of POA, which probably occurs through coordination of GA with a Rh atom, predominates among the side reactions. The optimum conditions for hydroformylation of CH₂O were found to be: RhCl₃ + PPh₃ as the catalyst,T 383 K, 12MPa, [H₂O] 1.8 mol L^–1, [Rh] 2.5 · 10^–3 g-at. L^–1, and [CH₂O] 0.03 g L^–1. At a substrate conversion of 62–67 %, the selectivity of GA formation reaches 96 %, and the yield is 60–65 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 75–78, January, 1995.     

From chiral and prochiral N-allylpyrroles to stereodefined pyrrole fused architectures: A particular application of the rhodium-catalyzed hydroformylation

We review our recent results on the rhodium-catalyzed hydroformylation of chiral and prochiral N-allylpyrroles as a synthetic route to stereodefined 5,6-dihydro- and 5,6,7,8-tetrahydroindolizines. The indolizine nucleus at different degrees of unsaturation is a building block of natural and synthetic target compounds; thus new approaches, especially if stereoselective and/or stereospecific, are highly desirable. The construction of the indolizine architectures reported here occurs by formation of a C8-C9 bond through intramolecular cyclization of the 4-pyrrolylbutanal intermediate.     

α-Amino acids as acid components in the Passerini reaction: influence of N-protection on the yield and stereoselectivity

The Passerini reaction offers an easy access to depsipeptides, when both acid and isocyanide are derived from α-amino acids. However, racemisation of isocyanides derived from α-amino acid esters severely limits their use in the Passerini reaction. In order to overcome this limitation, a study on the influence of the α-amino acid N-protecting group on the yield and diastereoisomeric ratio of the product of the Passerini reaction was performed. Six different protecting groups were tested. Their influence turns out to be crucial and is not constant when the amino acid is changed. After optimisation, the Passerini reaction products with cyclohexanone as the carbonyl component were obtained with 99% yield and >98% de.     

High Diastereoselectivity in the Conjugate Addition of Functionalized Alcohols to a Chiral(E)-Nitroalkene

Nitr0alkenesareversatilesyntheticintermediatesaspowerfulelectron-deficientreactantsincycloadditionandconjugatadditionreacti0ntoproducealargevarietyfunctionalizedcarbocyclicrings'.Purthermore,thenitrogrouPcanbeconvertedintoawiderangeoffiinctionalities2-Al0ughDiels-Alderreaction3andcyclopropanationoffunctionalizedcarbonnucleophiles4toY-chiralnitr0alkenehavebeenreportedrecently.Sofarthedetailedresearch0ftheconjugateadditionsoffimctionalizedalcoholst0chira1nitf0keneshasn0tbeenreported.Herewewish…     

Selectivities in the reaction of vicinal diimines and acyl chlorides

The reaction of vicinal diimines and acyl chlorides in the presence of triethylamine produces 3-imino-β-lactams and/or bis-β-lactams chemo-, regio-, and stereoselectively, which are important intermediates in pharmaceutical and organic synthesis. The selectivities in the reaction have been investigated. The results indicate that all diimines react with various ketenes generated from acyl chlorides in the presence of triethylamine to give rise to cis-4-imino-β-lactams (mono-cis-β-lactams) diastereoselectively due to the electron-withdrawing property of the imino group in the vicinal diimines. Bis-β-lactams were obtained from diimines via the mono-cis-β-lactams as intermediates. Only ketenes with strong electron-donating substituents can react with the mono-cis-β-lactams to yield bis-β-lactams, affording a pair of C2-symmetric cis-bis-β-lactams with symmetric diimines, two or four pairs of diastereomeric bis-β-lactams with ketoaldehyde-derived unsymmetric diimines depending on the steric hindrance of their N-substituents. The current investigation provides very important information for the selective preparation of mono- and bis-β-lactams from vicinal diimines.     

On the origin of regio- and stereoselectivity in singlet oxygen addition to enecarbamates

The reactions of excited state singlet molecular oxygen ((1)Δ(g),(1)O(2)) continue to witness interesting new developments. In the most recent manifestation, (1)O(2) is tamed to react with enecarbamates in a stereoselective manner, which is remarkable, in view of its inherently high reactivity (Acc. Chem. Res. 2008, 41, 387). Herein, we employed the CAS-MP2(8,7)/6-31G* as well as the CAS-MP2(10,8)/6-31G* computations to unravel the origin of (i) diastereoselectivities in dioxetane or hydroperoxide formation and (ii) regioselectivity leading to a [2 + 2] cycloadduct or an ene product when (1)O(2) reacts with an oxazolidinone tethered 2-phenyl-1-propenyl system. The computed Gibbs free energy profiles for E- and Z-isomers when (1)O(2) approaches through the hindered and nonhindered diastereotopic faces (by virtue of chiral oxazolidinone) of the enecarbamates exhibit distinct differences. In the case of E-isomer, the relative energies of the transition structures responsible for hydroperoxide (ene product) are lower than that for dioxetane formation. On the other hand, the ene pathway is predicted to involve higher barriers as compared to the corresponding dioxetane pathway for Z-isomer. The energy difference between the rate-determining diastereomeric transition structures involved in the most favored ene reaction for E-enecarbamate suggests high diastereoselectivity. In contrast, the corresponding energy difference for Z-enecarbamate in the ene pathway is found to be diminishingly close, implying low diastereoselectivity. However, the dioxetane formation from Z-enecarbamate is predicted to exhibit high diastereoselectivity. The application of activation strain model as well as the differences in stereoelectronic effects in the stereocontrolling transition structures is found to be effective toward rationalizing the origin of selectivities reported herein. These predictions are found to be in excellent agreement with the experimental observations.     

The unusual 1,4-chelation-controlled nucleophilic addition to aldehydes with high stereoselectivity. A systematic study of stereoselectivity in the addition reaction of carbon nucleophiles to cis-substituted cyclopropanecarbaldehydes

The addition reaction of carbon nucleophiles to cis-substituted cyclopropanecarbaldehydes was systematically investigated. Ab initio calculations of model cyclopropanecarbaldehydes suggested that the bisected s-cis and s-trans conformers are the only two minimum energy conformers, which are stabilized due to the π-donating stereoelectronic effect of the cyclopropane ring. The experimental results of a series of substrates, that is, cyclopropanecarbaldehydes 1-5 bearing a cis-(tert-butyldiphenylsilyloxy)methyl group, a cis-benzyloxymethyl group, a cis-(p-methoxybenzyloxy)methyl group, cis-N,N-diethylcarbamoyl and trans-phenyl groups, and cis-(tert-butyldiphenylsilyloxy)methyl and trans-phenyl groups, respectively, showed that highly anti-selective Grignard additions could be realized. It turned out that it occurred via an unusual 7-membered 1,4-chelation-controlled pathway. Highly stereoselective Grignard addition via the chelation-controlled pathway occurred even in the reaction of the usually non-chelating silyl ether-type substrate 5. The results have great importance because the 1,4-chelation-controlled stereoselective addition reactions can indeed be realized. Under non-chelation conditions, the syn-products were produced with moderate stereoselectivity, which are likely to be formed via the bisected s-cis conformation-like transition state stabilized by the characteristic orbital interaction. These reactions, especially the chelation-controlled reaction, should be useful because of their t stereoselectivity and stereochemical predictability.     

Optically active alkylbipyridines as chiral ligands in asymmetric catalysis. Synthesis of 2-(2′-pyridyl)-5,6,7,8-tetrahydro-8,9,9-trimethyl-5,8-methanoquinoline and rhodium-promoted asymmetric transfer hydrogenation of acetophenone

The title compound, a new chiral alkyl 2,2′- bipyridine containing a rigid alkyl framework, can be prepared through a six-step reaction sequence from (+)-camphor. Coordination of the new ligand to rhodium(I) procatalysts occurs with difficulty and the resulting species display a very low stereoselectivity in the catalytic transfer hydrogenation of acetophenone.     

Variational transition state theory as a tool to determine kinetic selectivity in reactions involving a valley-ridge inflection point

Variational transition state theory has been used to calculate the kinetic isotope effects affecting product ratios in the reaction between (1)O(2) and d(6)-tetramethylethylene. The minimum energy path on the potential energy surface for this process reaches a valley-ridge inflection point and then bifurcates leading to the two final products. Using canonical variational transition state theory, two distinct dynamical bottlenecks were located corresponding to the H- and the D-abstraction, respectively. The calculated KIE at 263 K turns out to be 1.126. Analogously, a H/T KIE of 1.17 at the same temperature has been found for the reaction of (1)O(2) with the tritiated derivative of tetramethylethylene.     

2-Lithio-N-BOC-thiazolidines as chiral acyl anion synthons: evaluation of facial stereoselectivity in the addition of chiral organolithiums to aldehydes

Deprotonation of N-BOC-thiazolidines having an isopropyl group in the 4- or 5-position affords chiral organolithiums that add to aldehydes in excellent yields. The relative and absolute configurations at both new stereocenters of the major and minor isomers were deduced. Mechanistic considerations suggest that each organolithium adds with a high degree of diastereoselectivity. We also demonstrated, as proof of principle, that further elaboration of the addition products into α-hydroxyaldehydes and glycols can be achieved.     

Optimal descriptors as a tool to predict the thermal decomposition of polymers

Quantitative structure-property relationship for the thermal decomposition of polymers is suggested. The data on architecture of monomers is used to represent polymers. The structures of monomers are represented by simplified molecular input-line entry system. The average statistical quality of the suggested quantitative structure-property relationships for prediction of molar thermal decomposition function $\hbox {Y}_{\mathrm{d},1/2}$ is the following: $\hbox {r}^{2}=0.970 \pm 0.01$ and $\hbox {RMSE}=4.71\pm 1.01\,(\hbox {K}\times \hbox {kg}\times \hbox {mol}^{-1})$ .     

Regio- and diastereoselective synthesis of (3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4] propellanes from 4-substituted 1,2-cyclohexanediones and o-aminophenols, a computational approach to regioselectivity prediction

The regio- and diastereoselective condensation reactions between 4-Me and 4-t-Bu substituted 1,2-cyclohexanediones and substituted o-aminophenols yielding the [4.4.4] propellane derivatives have been studied. The possibility of using semi-empirical PM3 calculations for rationalization and prediction of the regioisomer formation has been studied.     

Directed regio- and stereoselective hydroformylation of mono- and 1,3-disubstituted allylic alcohols: a catalytic approach to the anti-aldol-retron

Regioselective and diastereoselective hydroformylation of mono- and 1,3-disubstituted allylic alcohol o-DPPB esters is described. The products represent synthetically important anti-aldol retrons.     

Cycloadditions of nitrile oxides and nitrones to 4,4-methylene-1-methylpiperidine: Studies in regio- and stereoselectivity

Summary A series of spiro-substituted isoxazole derivatives were synthesized by 1,3-dipolar cycloadditions of nitrile oxides and nitrones to 4,4-methylene-1-methylpiperidine. Since nmr studies confirmed that only one regioisomer was formed selectively, semi-empirical quantum mechanical methods (AM1) were used to rationalize this regiochemical preference via calculation and inspection of HOMO-LUMO-energy and coefficients. X-ray structure analysis carried out for one of these products showed the occurrence of only one stereoisomer, explicable by comparing AM1-calculated H _f -values of all possible cycloadducts.Part XXXI in the series 1,3-Dipolar Cycloaddition on Heterocycles. Part XXX [Ref. 5]     

Effect of composition of the aqueous phase on catalytic properties of RhCl3 modified with a polycation in hydroformylation of 1-hexene

Water-soluble catalytic systems based on RhCl₃ and the salts of polycations (poly-N,N-diallyl-N,N-dimethylammonium chloride and poly-N,N-diallyl-N-methylaminodihydrophosphate) have been studied. It has been established that the rate of hydroformylation of 1-hexene increases with increasing pH of the aqueous phase. The replacement of the alkyl group at the nitrogen atom with the hydrogen atom in a polycation makes it possible to form a stable catalytic system at pH 5. The addition of low molecular electrolytes (NaCl, Na₂SO₄, and NaPO₄) also affects the catalytic properties of the studied catalytic systems. Stability of a catalytic system is enhanced with increasing charge of an anion of a low molecular electrolyte, which is, apparently, due to formation of intra- and intermolecular bonds in polyelectrolytes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1943–1945, October, 1995.     

Change of topology of the chemical interaction stage as a tool for the stereoselectivity control of PTC reactions

The relationship between the rate-limiting step of PTC and the site of the chemical interaction stage has been established for the cyclotriphosphazenes phenolysis reaction in liquid-liquid systems. Transfer of the site of the phenolysis of mono(aryloxy)cyclo-triphosphazenes from the bulk of the organic phase to the interface results in a change in the ratio of the products of the reaction ofcis- andtrans- isomers of bis(aryloxy)cyclo-triphosphazenes.In memory of the 75th anniversary of Member of the Academy of Sciences of Ukrainian SSR L. M. Litvinenko.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2102–2107, November, 1995.     

Markovnikov hydroformylation catalyzed by ROPAC in the presence of phosphine and phosphine oxide ligands

Rhodium-catalyzed hydroformylation of 1-octene in the presence of different phosphine and phosphine oxide ligands has been investigated. The molecular structure of new phosphine ligand, fluorenylidine methyl phenyl diphenylphosphine, was determined by single-crystal X-ray crystallography. Parameters such as different ligands, molar ratio of ligand to rhodium complex, ratio of olefin to rhodium complex, pressure of CO : H₂ mixture, and time of the reaction were studied. The linear aldehyde was the main product when the phosphine ligands were used as auxiliary ligands while the selectivity was changed to the branched products when the related phosphine oxide ligands were used. Under optimized reaction conditions, in the presence of [Rh(acac)(CO)(Ph₃P)]-di(1-naphthyl)phenyl phosphine oxide, conversion of 1-octene reached 97% with 87% selectivity of branched aldehyde.     

Origin of the regio- and stereoselectivity in palladium-catalyzed electrophilic substitution via bis(allyl)palladium complexes

Palladium-catalyzed allylic substitution of aryl allyl chlorides with aromatic and heteroaromatic aldehydes was performed in the presence of hexamethylditin. This procedure involves palladium-catalyzed formation of transient allylstannanes followed by generation of a bis(allyl)palladium intermediate, which subsequently reacts with the aldehyde electrophile. The catalytic substitution reaction proceeds with high regio- and stereoselectivity. The stereoselectivity is affected by the steric and electronic properties of the allylic substituents. Various functionalities including NO(2), COCH(3), Br, and F groups are tolerated under the applied catalytic conditions. Density functional calculations at the B3PW91/DZ+P level of theory were applied to study the steric and electronic effects controlling the regio- and stereoselectivity of the electrophilic addition. The development of the selectivity was studied by modeling the various bis(allyl)palladium species occurring in the palladium-catalyzed substitution of cinnamyl chloride with benzaldehyde. It was found that the electrophilic attack proceeds via a six-membered cyclic transition state, which has a pronounced chair conformation. The regioselectivity of the reaction is controlled by the location of the phenyl group on the eta(1)-allyl moiety of the complex. The stereoselectivity of the addition process is determined by the relative configuration of the phenyl substituents across the developing carbon-carbon bond. The lowest energy path corresponds to the formation of the branched allylic isomer with the phenyl groups in anti configuration, which is in excellent agreement with the experimental findings.