Sequential Dehydration Research Articles

Biomimetic synthesis of myrtucommulone K, N and O

A concise total synthesis of myrtucommulone K, N and O have been developed in 4 steps from commercially available materials. The synthetic strategy was inspired primarily by the biogenetic hypothesis and firstly enabled via a reduction, dehydration sequence for preparing isobutylidenesyncarpic acid followed by a hetero-Diels-Alder reaction to disclose the target moleculars. In this approach the exocyclic double bond of (−)-β-caryophyllene was more active than the endocyclic one in hetero-Diels–Alder reaction as the dienophile. The route is protecting-group-free, concise step, redox and pot economy.

Long-Chain Alkyl Cyanides: Unprecedented Volatile Compounds Released by Pseudomonas and Micromonospora Bacteria.

The analysis of volatiles from bacterial cultures revealed long-chain aliphatic nitriles, a new class of natural products. Such nitriles are produced by both Gram-positive Micromonospora echinospora and Gram-negative Pseudomonas veronii bacteria, although the structures differ. A variable sequence of chain elongation and dehydration in the fatty acid biosynthesis leads to either unbranched saturated or unsaturated nitriles with an ω-7 double bond, such as (Z)-11-octadecenenitrile, or methyl-branched unsaturated nitriles with the double bond located at C-3, such as (Z)-13-methyltetradec-3-enenitrile. The nitrile biosynthesis starts from fatty acids, which are converted into their amides and finally dehydrated. The structures and biosyntheses of the 19 naturally occurring compounds were elucidated by mass spectrometry, synthesis, and feeding experiments with deuterium-labeled precursors. Some of the nitriles showed antimicrobial activity, for example, against multiresistant Staphylococcus aureus strains.

New catalytic strategies for α,ω-diols production from lignocellulosic biomass.

Catalytic strategies for the synthesis of 1,5-pentanediol (PDO) with 69% yield from hemicellulose and the synthesis of 1,6-hexanediol (HDO) with 28% yield from cellulose are presented. Fractionation of lignocellulosic biomass (white birch wood chips) in gamma-valerolactone (GVL)/H2O generates a pure cellulose solid and a liquid stream containing hemicellulose and lignin, which is further dehydrated to furfural with 85% yield. Furfural is converted to PDO with sequential dehydration, hydration, ring-opening tautomerization, and hydrogenation reactions. Acid-catalyzed cellulose dehydration in tetrahydrofuran (THF)/H2O produces a mixture of levoglucosenone (LGO) and 5-hydroxymethylfurfural (HMF), which are converted with hydrogen to tetrahydrofuran-dimethanol (THFDM). HDO is then obtained from hydrogenolysis of THFDM. Techno-economic analysis demonstrates that this approach can produce HDO and PDO at a minimum selling price of $4090 per ton.

One-pot conversion of biomass-derived xylose to furfuralcohol by a chemo-enzymatic sequential acid-catalyzed dehydration and bioreduction

One-pot furfuralcohol (FOL) productionviadehydration of corncob-derived xylose followed by bioreduction of furfural has been described.

Experimental and theoretical assessment of the mechanism and site requirements for ketonization of carboxylic acids on oxides

Ketonization of carboxylic acids removes O-atoms and forms new CC bonds, thus providing routes from sustainable carbon feedstocks to fuels and chemicals. The elementary steps involved and their kinetic relevance, as well as the number and nature of the active sites on active TiO2 and ZrO2 catalysts, remain matters of active discourse. Here, site titrations demonstrate the requirement for coordinatively-unsaturated M-O-M sites (M=Ti, Zr) with specific geometry and intermediate acid-base strength. The measured site densities allow rigorous reactivity comparisons among catalysts based on turnover rates and activation free energies, as well as the benchmarking of mechanistic proposals against theoretical assessments. Kinetic, isotopic, spectroscopic, and theoretical methods show that C2C4 acids react on anatase TiO2 via kinetically-relevant CC coupling between 1-hydroxy enolate species and coadsorbed acids bound at vicinal acid-base pairs saturated with active monodentate carboxylates. Smaller TiTi distances on rutile TiO2 lead to the prevalence of unreactive bidentate carboxylates and lead to its much lower ketonization reactivity than anatase. The prevalent dense monolayers of chemisorbed acid reactants reflect their strong binding at acid-base pairs and their stabilization by H-bonding interactions with surface OH groups derived from the dissociation of the carboxylic acids or the formation of 1-hydroxy enolates; these interactions also stabilize CC coupling transition states preferentially over their carboxylate precursors; high coverages favor sequential dehydration routes of the α-hydroxy-γ-carboxy-alkoxide CC coupling products over previously unrecognized concerted six-membered-ring transition states. Infrared spectra show that ubiquitous deactivation, which has precluded broader deployment of ketonization in practice and unequivocal mechanistic inquiries, reflects the gradual formation of inactive bidentate carboxylates. Their dehydration to ketene-like gaseous species is faster on anatase TiO2 than on ZrO2 and allows the effective scavenging of bidentate carboxylates via ketene hydrogenation to alkanals/alkanols on a Cu function present within diffusion distances. These strategies make anatase TiO2, a more effective catalyst than ZrO2, in spite of its slightly lower initial turnover rates. This study provides details about the mechanism of ketonization of C2C4 carboxylic acids on TiO2 and a rigorous analysis of the sites required and of active and inactive bound species on TiO2 and ZrO2. The preference for specific distances and for intermediate acid-base strength in M-O-M species is consistent with the structure and energy of the proposed transition states and intermediates; their relative stabilities illustrate how densely-covered surfaces, prevalent during ketonization catalysis, represent an essential requirement for the achievement of practical turnover rates.

Facile Synthesis of Polycyclic Aromatic Hydrocarbons: Brønsted Acid Catalyzed Dehydrative Cycloaromatization of Carbonyl Compounds in 1,1,1,3,3,3‐Hexafluoropropan‐2‐ol

The cycloaromatization of aromatic aldehydes and ketones was readily achieved by using a Brønsted acid catalyst in 1,1,1,3,3,3‐hexafluoropropan‐2‐ol (HFIP). In the presence of a catalytic amount of trifluoromethanesulfonic acid, biaryl‐2‐ylacetaldehydes and 2‐benzylbenzaldehydes underwent sequential intramolecular cationic cyclization and dehydration to afford phenacenes and acenes, respectively. Furthermore, biaryl‐2‐ylacetaldehydes bearing a cyclopentene moiety at the α‐position underwent unprecedented cycloaromatization including ring expansion to afford triphenylenes. HFIP effectively promoted the cyclizations by suppressing side reactions presumably as a result of stabilization of the cationic intermediates.

Two-Step Synthesis of (Z)-3-Aryl-5-(arylmethylidene)butenolides by an Ivanov Reaction/Silver(I)-Catalyzed Lactonization/In Situ Dehydration Sequence

A stereoselective synthesis of the title compounds was developed. Hexane- and amine-free THF solutions of α-lithiated lithium arylacetates (‘arylacetic acid dianions’) were aldol-added to 3-arylpropynals. This gave 2,5-diaryl-3-hydroxypent-4-ynoic acids with up to a 72:28 preference for the <i>anti</i>-diastereomer (27 examples + 1 exception). When treated with Ag₂CO₃ (1–20 mol%) in DMF at room temperature for 2.5 days, the respective mixtures underwent regio- and stereoselective lactonizations followed by an in situ dehydration. Thereby 3-aryl-5-(arylmethylidene)butenolides were obtained with a <i>Z</i>-configuration of the oxygenated C=C bond. Their overall yields ranged from 46% to 83% (1 exception: 28%). Three 3-aryl-5-(arylmethyli­dene)butenolides contained a C–Br and/or a C–I bond. They allowed a subsequent Pd-catalyzed C–C coupling, which furnished follow-up butenolides.

Direct Assembly of Prenylated Heteroarenes through a Cascade Minisci Reaction/Dehydration Sequence.

The prenyl group is an important component in bioactive compounds. Herein, we report the assembly of prenylated heteroarenes through a cascade Minisci reaction and acid‐promoted dehydration sequence. The use of potassium (3‐hydroxy‐3‐methylbut‐1‐yl)trifluoroborate as a new coupling reagent allows the direct introduction of prenyl and 3‐hydroxy‐3‐methylbutyl groups to a wide variety of electron‐deficient heteroarenes. Synthetic application is also demonstrated.

Modular Regiospecific Synthesis of Nitrated Fatty Acids

Endogenous nitrated fatty acids are an important class of signaling molecules. Herein a modular route for the efficient and regiospecific preparation of nitrooleic acids as well as various analogues is described. The approach is based on a simple set of alkyl halides as common building blocks and a Henry reaction/Burgess dehydration sequence for the formation of the key nitroalkene moiety.

ChemInform Abstract: Synthesis of Multisubstituted Pyridin‐2(3H)‐ones via Nickel‐Catalyzed Intermolecular Condensation of β‐Ketobutylanilides.

A nickel-catalyzed intermolecular condensation of β-ketobutylanilides to synthesize multi-substituted pyri-din-2(3H)-ones was described. To the best of our knowledge, there is no report on the synthesis of these compounds. All the tested substrates with various functional groups irrespective of their nature, whether electron-donating or –withdrawing, and the location of the substituents on the aromatic rings, were all tolerated under the standard conditions and smoothly transformed into the desired products with 71 %-86 % yields. This strategy provides an efficient approach to valuable pyridin-2(3H)-ones via a sequential dehydration processes which may find applications in natural products and medicinal chemistry.

ChemInform Abstract: Synthesis of 2‐Alkenylquinoline by Reductive Olefination of Quinoline N‐Oxide under Metal‐Free Conditions.

AbstractThe reaction is proposed to proceed via a 1,3‐dipolar cycloaddition/acid‐assisted ring‐opening/dehydration sequence.

Synthesis of Multisubstituted Pyridin‐2(3H)‐ones via Nickel‐Catalyzed Intermolecular Condensation of β‐Ketobutylanilides

AbstractA nickel‐catalyzed intermolecular condensation of β‐ketobutylanilides to synthesize multi‐substituted pyri‐din‐2(3H)‐ones was described. To the best of our knowledge, there is no report on the synthesis of these compounds. All the tested substrates with various functional groups irrespective of their nature, whether electron‐donating or –withdrawing, and the location of the substituents on the aromatic rings, were all tolerated under the standard conditions and smoothly transformed into the desired products with 71 %‐86 % yields. This strategy provides an efficient approach to valuable pyridin‐2(3H)‐ones via a sequential dehydration processes which may find applications in natural products and medicinal chemistry.

A Census of Tetrahedral Hyperbolic Manifolds

ABSTRACTWe call a cusped hyperbolic 3-manifold tetrahedral if it can be decomposed into regular ideal tetrahedra. Following an earlier publication by three of the authors, we give a census of all tetrahedral manifolds and all of their combinatorial tetrahedral tessellations with at most 25 (orientable case) and 21 (non-orientable case) tetrahedra. Our isometry classification uses certified canonical cell decompositions (based on work by Dunfield, Hoffman, and Licata) and isomorphism signatures (an improvement of dehydration sequences by Burton). The tetrahedral census comes in Regina as well as SnapPy format, and we illustrate its features.

One‐Pot Deoxygenation of Fructose to Furfuryl Alcohol by Sequential Dehydration and Decarbonylation

AbstractFructose was deoxygenated to furfuryl alcohol (FFA) by tandem dehydration and decarbonylation in one pot over the AlCl3⋅6 H2O/Pd(OAc)2 catalyst combination to give a high FFA yield of 40.6 %. AlCl3⋅6 H2O behaves as an effective Lewis acid to catalyze the dehydration of fructose to 5‐hydroxymethylfurfural (HMF), and subsequently, Pd(OAc)2 catalyzes the removal of a CO moiety from HMF to produce FFA selectively. The hydroxyl group on the HMF intermediate was stabilized by poly(1‐vinyl‐2‐pyrrolidinone) through an intermolecular hydrogen bond, which accelerated the dehydration of fructose and inhibited the hydrogenation of HMF by formic acid. The decarbonylation of HMF was promoted and the unwanted decomposition of fructose was inhibited through the use of 4 Å molecular sieves. This research highlights a “one‐pot” catalytic system to transform renewable carbohydrates into fine chemicals by tandem dehydration and decarbonylation reactions without the separation or purification of HMF.

Homochiral crystal generation via sequential dehydration and Viedma ripening

1,2-Bis(N-benzoyl-N-methylamino)benzene (2) forms centrosymmetric hydrate crystals (2·xH2O) and non-centrosymmetric anhydrous crystals. Dehydration of this hydrate (30 min at 140 °C) resulted in the formation of chiral crystals (i.e. a physical racemate of the conglomerate crystals) as verified using solid-state circular dichroism and powder X-ray diffraction. Subsequent attrition-enhanced deracemization, also known as Viedma ripening, was used to obtain homochiral crystals of 2 within 5 h.

Water-dispersible boronate nanoparticles as support materials for noble metals in the hydrogenation of levulinic acid to γ-valerolactone

The sequential dehydration reaction of benzene-1,4-diboronic acid with pentaerythritol in the presence of polyethyleneimine (PEI) led to polymeric 3-benzo-2,4,8,10-tetraoxa- 3,9-diboraspiro[5.5]undecane, resulting in the formation of a PEI-coated boronate nanoparticle (BNP) with a mean diameter of 121 ± 43 nm through the spontaneous self-assembly. Subsequently, noble metal deposition on the boronate particle (M/BNP, M = Ru, Pd and Pt) was successfully achieved by NaBH4 reduction of RuCl3, and in the presence of BNP. Exploration of boronate-based catalytic systems applicable to the conversion of biomass to chemicals revealed that Ru/BNP has excellent catalytic activity for the hydrogenation of levulinic acid to γ-valerolactone (GVL) in H2O under 0.8 MPa of H2 at 100 °C; after 4 h, the reaction afforded GVL in 94.6% yield. The catalytic performance and recyclability of Ru/BNP in the reaction were investigated.

ChemInform Abstract: Efficient Synthesis of Highly Enantioenriched Δ1‐Pyrrolines.

AbstractThe title compounds are efficiently obtained by a one‐pot nitro‐reduction, cyclization, and dehydration sequence from (R,E)‐1,5‐diaryl‐3‐(nitromethyl)‐5‐pent‐4‐en‐1‐ones.

Raman spectral classification of mineral- and collagen-bound water's associations to elastic and post-yield mechanical properties of cortical bone

Water that is bound to bone's matrix is implied as a predictor of fracture resistance; however, bound water is an elusive variable to be measured nondestructively. To date, the only nondestructive method used for studying bone hydration status is magnetic resonance variants (NMR or MRI). For the first time, bone hydration status was studied by short-wave infrared (SWIR) Raman spectroscopy to investigate associations of mineral-bound and collagen-bound water compartments with mechanical properties. Thirty cortical bone samples were used for quantitative Raman-based water analysis, gravimetric analysis, porosity measurement, and biomechanical testing. A sequential dehydration protocol was developed to replace unbound (heat drying) and bound (ethanol treatment) water in bone. Raman spectra were collected serially to track the OH-stretch band during dehydration. Four previously identified peaks were investigated: I3220/I2949, I3325/I2949 and I3453/I2949 reflect status of organic-matrix related water (mostly collagen-related water) compartments and collagen portion of bone while I3584/I2949 reflects status of mineral-related water compartments and mineral portion of bone. These spectroscopic biomarkers were correlated with elastic and post-yield mechanical properties of bone. Collagen–water related biomarkers (I3220/I2949 and I3325/I2949) correlated significantly and positively with toughness (R2=0.81 and R2=0.79; p<0.001) and post-yield toughness (R2=0.65 and R2=0.73; p<0.001). Mineral-water related biomarker correlated significantly and negatively with elastic modulus (R2=0.78; p<0.001) and positively with strength (R2=0.46; p<0.001). While MR-based techniques have been useful in measuring unbound and bound water, this is the first study which probed bound-water compartments differentially for collagen and mineral-bound water. For the first time, we showed an evidence for contributions of different bound-water compartments to mechanical properties of wet bone and the reported correlations of Raman-based water measurements to mechanical properties underline the necessity for enabling approaches to assess these new biomarkers noninvasively in vivo to improve the current diagnosis of those who may be at risk of bone fracture due to aging and diseases.

Solid State Reaction Mechanisms of the LiMnPO4 Formation Using Special Function and Thermodynamic Studies

LiMnPO4 was successfully synthesized via thermal decomposition processes of the synthesized MnHPO4·3H2O precursor. Thermogravimetry/differential thermal gravimetry/differential thermal analysis, Fourier transform infrared, atomic absorption spectrophotometry, X-ray diffraction, and scanning electron microscopy techniques were employed for the characterization of the samples. Three thermal decomposition steps in the sequence of dehydration, polycondensation, and decarbonization were observed. The iterative Kissinger–Akahira–Sunose method was used to calculate the exact Eα values. Regions I and II of the first, second, and final steps were confirmed to be single-step kinetic processes with the unique kinetic triplets. The most probable mechanism functions were found to be R3, R2, A2, and P4 corresponding to contracting sphere, contracting cylinder, assumed random nucleation (its subsequent growth), and nucleation processes, respectively. The pre-exponential factors, A, were calculated using Eα and g(α). The...

Synthetic studies on aculeximycin: synthesis of C24-C40 segment by Kobayashi aldolization and epoxide rearrangements.

Stereoselective synthesis of the C24-C40 segment of aculeximycin has been achieved by using the Kobayashi aldol reactions and epoxy-opening rearrangement reactions. The C33-C40 segment was synthesized by the Kobayashi aldol reaction followed by epoxidation and Jung rearrangement of epoxide 9, while the C25-C32 segment was constructed by the Kobayashi aldol reaction followed by epoxidation and the epoxy-opening rearrangement reaction of epoxide 13. These segments were connected by the aldol reaction and the sequential dehydration, reduction, and conversion of ethyl ester to ethyl ketone to give the C24-C40 segment 1. All stereogenic centers were constructed by substrate-controlled stereoselective reactions.