Kinetics of the reactions of hydroxyl radical with aliphatic aldehydes

Rate coefficients for OH reactions with the 2–5 carbon aliphatic aldehydes have been measured under pseudo first-order conditions in OH. OH was generated by flash photolysis of H₂O at wavelengths greater than 165 nm and its concentration monitored using time-resolved resonance fluorescence spectroscopy. Two reactions were studied only at 298 K while five reactions were studied over the temperature range 250–425 K; negative activation energies were observed for all five reactions. Aldehyde reactivity toward OH is nearly independent of the identity of the hydrocarbon side chain. Our results are compared with those obtained in previous studies of OH-aldehyde reaction kinetics and their mechanistic implications are discussed.     

Practical and highly selective oxazolidinethione-based asymmetric acetate aldol reactions with aliphatic aldehydes

[reaction: see text] The utility of a valine-derived oxazolidinethione for auxiliary-based asymmetric acetate aldol reactions is reported. Titanium(IV) chloride, along with (-)-sparteine and N-methylpyrrolidinone, is employed for enolization. Subsequent aldol reaction with aliphatic aldehydes occurs with high diastereoselectivity (from 92:8 to 99:1 dr).     

Haloacrylic acids XI. Photochemical reactions of aliphatic aldehydes with methyl trifluoroacrylate

Photochemically initiated reactions of aliphatic aldehydes, namely acetaldehyde, propionaldehyde and butyraldehyde, with methyl trifluoroacrylate afforded γ-ketoesters of the type R-CO-CF₂CHF-COOCH₃ in the liquid phase. In the gas phase reaction further products were formed by addition of the aldehyde fragments to the olefinic bond of the methyl trifluoroacrylate.     

Aqueous Barbier allylation of aldehydes mediated by tin

The aqueous tin-mediated Barbier reaction affords good to excellent yields and moderate syn diastereoselectivity under basic and acidic conditions. The high yields and stereoselectivity observed in the case of o-substituted aldehydes suggest a cyclic organotin intermediate or transition state in K2HPO4 solution. A practical and efficient aqueous tin allylation of methoxy- and hydroxybenzaldehydes can be carried out in HCl solution in 15 minutes to afford the corresponding homoallylic alcohols in high yields. Aliphatic aldehydes give moderate to excellent yields with reaction times ranging from 30 to 60 minutes. Under these conditions, crotylation gives exclusively the gamma-product and the syn isomer is formed preferentially. For 2-methoxybenzaldehyde, an equilibration of the isomers to a syn/anti ratio of 1:1 can be observed after several hours. Control experiments with radical sources or scavengers give no support for radical intermediates. NMR studies suggest a mechanism involving an organotin intermediate. The major organotin species formed depends on the reaction medium and the reaction time. The use of acidic solution reduces the reaction times, due to the acceleration of the formation of the allyltin(IV) species.     

Zirconium-catalyzed asymmetric Kabachnik–Fields reactions of aromatic and aliphatic aldehydes

An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik–Fields reaction to give α-aminophosphonates. A catalyst was sought that would give high asymmetric inductions for aromatic and, and more particularly, for aliphatic aldehydes since there has not previously been an effective catalyst developed for this class of aldehydes. The optimal catalyst is prepared from three equivalents of the 7,7′-di-t-butylVANOL ligand, one equivalent of N-methylimidazole and one equivalent of zirconium tetraisopropoxide. This catalyst was most efficient in the presence of 10 mol% benzoic acid. Optimal conditions for aryl aldehydes required the use of 3,5-diisopropyl-2-hydroxyaniline and gave the aryl α-aminophosphonates in up to 96% yield and 98% ee over 11 different aryl aldehydes. The best aniline for aliphatic aldehydes was found to be 3-t-butyl-2-hydroxyaniline and gave the corresponding phosphonates in up to 83% yield and 97% ee over 18 examples. The asymmetric inductions for aliphatic aldehydes were comparable with those for aromatic aldehydes with a mean induction of 90% ee for the former and 91% ee for the latter. The best method for the liberation of the free amine from the aniline substituted α-aminophosphonates involved oxidation with N-iodosuccinimide.

An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik–Fields reaction to give α-aminophosphonates.     

Condensation of gem-dinitroalkanes with aliphatic aldehydes and amines

Summary Gem-dinitroalkanes condense readily with acetaldehyde, propionaldehyde, butyraldehyde, and amines. The use of these aldehydes instead of formaldehyde extends the field of application of the Mannich reaction with nitro compounds.     

Regioselective Barbier reactions of 2-bromomethylcyclohexenone

Although the addition of crotyl or prenyl organometallic reagents has certainly found application in organic synthesis, the use of other non-symmetric allylic organometallic reagents has not received much attention. In part this is due to potential problems in controlling the regioselectivity of the addition products. We have noted that the tin and zinc reagents derived from 2-bromomethylcyclohexenone afford the complementary α and γ addition products, respectively. These conditions work for the reaction with a range of aldehydes, affording the products in good to modest yield.     

Cyclocondensation of lower aliphatic aldehydes with arylamines and cyclopentadiene

Three-component condensation of lower aliphatic aldehydes (C₁-C₃) with arylamines and cyclopentadiene (the Povarov reaction) gave 3a,4,5,9b-tetrahydro-3H-cyclopenta[c]-quinolines. Ozonization of their N-trifluoroacetyl derivatives afforded the corresponding ozonides. Cyclocondensation of 4-fluoroaniline with formaldehyde and cyclopentadiene gave earlier unknown 2-fluoro-3b,6,6a,7,9,9a,10,12a-octahydrobenzo[i,j]dicyclopenta[b,g]quinolizine.     

1-alkoxyallene as an effective precursor for regio- and stereocontrolled allylation reactions with aliphatic aldehydes via bis-stannylation

Bis-stannylation of 1-(methoxy)methoxyallene yields (E)-(3-(methoxymethoxy)prop-2-ene-1,2-diyl) bis-tributylstannane (2) as a highly reactive allylation reagent. Stereoselective reactions of functionalized stannane 2 with a variety of aldehydes provide good yields of 1,2-diol derivatives. Reactions with alpha-alkoxyaldehydes proceed with chelation-controlled addition to afford efficient constructions of 3,4-anti-4,5-syn-relationships in stereotriads bearing three differentiated oxygen (alkoxy and hydroxy) substituents. Mechanistic considerations are presented, and derivatives for NMR experiments support the stereochemical assignments. An X-ray diffraction study is included.     

Reactions of aliphatic aldehydes under electron-impact

The mass spectra of hexanal, heptanal and nonanal variously labeled with deuterium confirm γ-hydrogen migration and β cleavage as the mechanism leading to [C₂H₄O]⁺˙ and [M ? C₂H₄O]⁺˙, although the data on the latter are complicated by contributions from other, related paths. In addition, they show that three other major primary decomposition products, [M ? C₂H₄]⁺˙, [M ? H₂O]⁺˙ and [C₃H₅O]⁺, all arise in large part by processes involving γ-hydrogen migration to the oxygen atom. The ethylene lost to yield the first of these products consists of the α and β methylene groups. The loss of ethylene most likely occurs by way of a cyclobutanol intermediate, which, via alternative reaction paths, may well contribute to the yields of the other two products as well. These findings further extend the range of parallelism between photochemical and electron-impact-induced reactions.     

Pyridoxal reactions with amines and aliphatic diamines

Interaction of pyridoxal (3-hydroxy-5-hydroxymethyl-2-methylisonicotinaldehyde) with amines, mono- and disubstituted diamines led to the formation of compounds having in their structure imine, imidazolidine, and pyrimidine moieties. Structure of the obtained compounds was proved by IR data, ¹H NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis.     

Montmorillonite clay-catalyzed cyclotrimerization and oxidation of aliphatic aldehydes

A temperature-dependent equilibrium is observed for the cyclotrimerization of aliphatic aldehydes in the presence of Montmorillonite K10 clay, while aerobic oxidation of aliphatic aldehydes to the corresponding carboxylic acids is favored at room temperature in the presence of Montmorillonite KSF clay.     

Samarium diiodide-mediated reductive couplings of chiral nitrones with aldehydes/ketones and acyl chlorides

The SmI₂-mediated and H₂O-promoted reductive cross-coupling reactions of the l-tartaric acid derived nitrone (3S,4S)-8 with aldehydes/ketones, and the l-malic acid derived nitrone (S)-6 with aliphatic acyl chlorides have been investigated, respectively. (2R,3S,4S)-1,3,4-Trihydroxyprolinol derivatives 9a-f were obtained with high C-2/C-3 trans-selectivities, and 72:28-85:15 diastereoselectivities at the carbinol center from aromatic ketones/aldehydes, while low diastereoselectivities for aliphatic aldehydes. Conditions have been established for the syntheses of (2R,3S,4S)-3,4-dihydroxyprolinol derivatives such as 18, by N-O bond cleavage of the corresponding N-hydroxyprolinol derivatives 9b-f, or more conveniently by a one-pot reductive coupling of nitrone 8 and in situ N-O bond cleavage of the resultant coupling product. The 2-acyl-3-benzyloxy-1-hydroxypyrrolidines 10a-f were formed in 48-82% yields, and in 74:26-78:22 diastereoselectivities. It was revealed that the amount of water required for the reaction is substrate-depending.     

The high-resolution mass spectra of aliphatic aldehydes

The mass spectra of the C₃ to C₉ n-alkanals and a number of branched aldehydes have been obtained at a resolution sufficient to resolve the O? CH₄ doublets. From the resolved spectra, a study of metastable transitions, and the spectrum of one deuterium-labelled alkanal, (n-hexanal-2,2-d₂) the major fragmentation reactions have been elucidated. Of particular interest are the γ-cleavage reaction, leading to [C₃H₅O]+ in the n-alkanals, which proceeds both by a simple cleavage and by cleavage preceded by hydrogen interchange, and the loss of C₂H₄, which involves loss of the C₂ and, probably C₃, carbons.     

Equilibrium cyclotrimerization of ether oxygen-substituted aliphatic aldehydes

This article describes the equilibrium cyclotrimerization of β-methoxypropionaldehyde (MPA), 4,7-dioxaoctanal (DOA), and n-octanal (OA) initiated by boron trifluoride etherate in toluene at a temperature range of ?10 to 25°C. The enthalpy and entropy changes corresponding to the conversion of 1 mole of the monomers to 1/3 mole of their cyclic trimers in toluene solution, at the initial monomer concentration of 1 mole/liter, were evaluated as follows: ΔH_ss = ?5.9 ± 0.3 kcal/mole and ΔS_ss = ?19.1 ± 1.3 cal/mole deg for the MPA system; ΔH_ss = ?7.4 ± 0.4 kcal/mole and ΔS_ss = ?24.1 ± 1.7 cal/mole deg for the DOA system; ΔH_ss = ?6.1 ± 0.4 kcal/mole and ΔS_ss = ?21.2 ± 1.5 cal/mole deg for the OA system. The comparison of these values with those in their polymerization indicates that the cyclotrimerization of aldehydes is thermodynamically of greater advantage than their polymerization. The effects of long and polar substituents are discussed from the view-point of the intermolecular interactions by the polar groups in monomers and their cyclic trimers.     

Ligand enabled none-oxidative decarbonylation of aliphatic aldehydes

Decarbonylation of aldehydes is a basic organic transformation, which has been developed for more than six-decade. However, as comparing to well-studied aromatic aldehydes, fewer examples for catalytic decarbonylation of aliphatic aldehydes were reported, mainly on simple or special substrates. For α-bulky or highly functionalized ones, stoichiometric Rh(I) were usually required for decent yields. Herein, we present a rare example of Ir(I)-catalyzed direct decarbonylation of α-quaternary aldehydes with broad substrate scope and good functional group compatibility via judicious selection of ligand. The α-chirality is memorized in this decarbonylation process. In addition, we report a broad-spectrum decarbonylation of α-secondary and α-tertiary aldehydes containing multifunctional groups with an improved Rh(I)/DPPP recipe. Finally, we realized selective decarbonylation of α-tertiary aldehydes in the presence of α-quaternary one via the reactivity differences.