Isomerization of alkyl allyl and allyl silyl ethers catalyzed by ruthenium complexes

Preparation of New Glycerol-Based Dendrimers and Studies on Their Behavior toward Essential Oil Encapsulation

Two new families of glycerol-based dendrimers (glyceroladendrimers (GADs) and glyceroclickdendrimers (GCDs)) have been synthesized. Three generations have been isolated for each family with good yields and were fully analyzed. The encapsulation of essential oils (citronella and cinnamon) in GADs, GCDs, and also in previously described glycerodendrimers GD-PAMAMs and GD-PPIs has been studied by dynamic-headspace gas chromatography coupled to mass spectrometry. The retention rates obtained were from -35.8 to 26.65% for citronella essential oil and from 2.14 to 38.84% for the cinnamon essential oil. In addition, the best results were obtained with GD-PAMAMs and GD-PPIs of higher generation. The interaction study between essential oils or more precisely their major components have been performed through NMR spectroscopy (¹H NMR and DOSY NMR). No direct interactions between dendrimers and essential oils have been observed, but a surprising behavior of compression of the dendrimer in stable emulsions was observed. Indeed, the hydrodynamic radius of GD-PPI-3 has been reduced in the presence of cinnamon essential oil.

Technological Aspects of Highly Selective Synthesis of Allyloxyalcohols—New, Greener, Productive Methods

Allyl ethers bearing free hydroxyl groups of CH2=CH-CH-O-A-OH type (hydroxyalkyl allyl ethers, allyloxyalcohols) are valuable chemicals in many environmentally friendly industrial applications. The development of technologically attractive methods for their production is necessary. The two pathways (L-L PTC and non-catalytic solvent-free conditions) were optimized for the highly selective and yield synthesis of 4-allyloxybutan-1-ol. Improvements in the PTC method (50% NaOH(aq), the equimolar ratio of NaOH to diol, cyclohexane as solvent) with a new highly selective and effective PT catalyst, i.e., Me(n-Oct)3N+Br− (0.3 mol%), resulted in 88% yield and 98% selectivity of 4-allyloxybutan-1-ol with minimal formation of allyl chloride hydrolysis by-products (<1%). In turn, application of non-catalytic solvent-free conditions and the change in the key substrate with an excess of diol and use of solid NaOH solely led to a mono-O-allylation product with an excellent yield of 99% in a relatively short reaction time (3.5 h), with trace amounts of by-products (<0.1%). This sustainable method is perfectly suitable for the synthesis on a larger scale (3 moles of the key substrate) and for the full O-allylation process.

Highly Productive Synthesis of 1-Propenyloxybutan-1-ol Under Solvent-Free Homogeneous Ruthenium Catalyst Conditions

The 1-propenyl ethers bearing free hydroxyl groups of CH3CH=CH–O–A–OH type (hydroxyalkyl 1-propenyl ethers, 1-propenyloxyalcohols) are the most desired as the reactive diluents for photopolymerizable systems with enhanced reactivity or intermediates for the synthesis of hybrid monomers for special applications. The ruthenium complexes-catalyzed isomerization of allyl ethers under solvent-free conditions is an atom-economical and environmentally sustainable method for their production. Here, the reaction conditions and limitations for the highly productive and selective synthesis of model 4-(1-propenyloxy)butan-1-ol have been investigated. The minimal loading of ruthenium pre-catalysts needed for completion of reaction within reasonable times was priority assumption. It was found that [RuClH(CO)(PPh3)3] or [RuCl2(PPh3)3] exhibited extremely high catalytic activity under optimized non-oxidative reaction conditions. The key effect of reaction temperature on the activation pre-catalyst and the exothermal effects of isomerization was discovered. The practically quantitative yields of 4-(1-propenyloxy)butan-1-ol were achieved with using of very low loading of [Ru] (5 ppm) and Bu3N (to maintain reaction chemoselectivity) at the temperature of 120 °C for only 0.5 h. Consequently, the attained TON (turnover number) and TOF (turnover frequency) values of ca. 198,000 and 390,000 h−1 were unprecedentedly high and industrial attractive. On the other hand, the direct recycling of ruthenium catalyst is not a reasonable method for improving catalyst productivity.

Technological aspects of synthesis of poly(ethylene glycol) mono-1-propenyl ether monomers

For the first time, the technological aspects of the highly productive and selective synthesis of UV-reactive poly(ethylene glycol) mono-1-propenyl ether monomers was developed. The solvent-free isomerization of model commercial available 2-allyloxyethanol and allyloxypoly(ethylene glycol) derivatives, type Allyl–[OCH2CH2] n –OH, n = 1–5, into a 1-propenyl derivative under the homogeneous catalysis conditions using the ruthenium complexes were evaluated. The effect of a various reaction conditions (i.e. the concentration of [Ru] complex, the reaction temperature, reaction gas atmosphere) together with trace amounts of allyl hydroperoxides formed via autoxidation reaction of allyl substrates on the productivity of catalyst was examined in detail. Moreover, the significant role of the allyl substrate structures on the catalytic activity of ruthenium catalysts were also recognized. The optimal parameters of the scaled-up synthesis together with productivity of catalyst were first established.

O-Allylated Pudovik and Passerini Adducts as Versatile Scaffolds for Product Diversification

The palladium-catalyzed O-allylation of α-hydroxyphosphonates and α-hydroxyamides obtained from Pudovik and Passerini multicomponent reactions has allowed interesting and highly straightforward access to a variety of building blocks for product diversification. These post-functionalizations include a selective base- or ruthenium hydride-mediated isomerization/Claisen rearrangement cascade and a ring-closing metathesis that allows access to a variety of diversely functionalized phosphono-oxaheterocycles.

Sequential Alkene Isomerization and Ring-Closing Metathesis in Production of Macrocyclic Musks from Biomass

We report successful utilization of sequential alkene isomerization and ring-closing metathesis of dec-9-enoic acid based dienes in synthesis of macrocyclic lactones that possess a strong scent of musk. This catalytic sequence was essential to trim the chain length of starting dienes to yield macrocycles of the right size. Dec-9-enoic acid is conveniently obtainable from oleic esters by Ru-catalysed ethenolysis.

Development of Small Molecular Proteasome Inhibitors Using a Caenorhabditis elegans Screen

We have developed a screening protocol to identify compounds with characteristics of small molecule proteasome inhibitors using the real-time analysis of the Caenorhabditis elegans germ line. This screen is able to identify compounds that induce germ line phenotypes characteristic of a reduction in proteasome function such as changes in polarity, aberrant nuclear morphology, and stimulation of apoptosis. This basic protocol is amenable to a high throughput (96-well) format and has been used successfully to identify multiple compounds for further analysis based on structural elements from the naturally occurring compounds lactacystin and the β-lactone homologs omuralide and salinosporamide A. The further development of this assay system should allow for the generation of novel small molecule proteasome inhibitors in a genetically tractable whole animal amenable to biochemical analysis.

Enantioselective synthesis of 3,4-chromanediones via asymmetric rearrangement of 3-allyloxyflavones

Asymmetric scandium(III)-catalyzed rearrangement of 3-allyloxyflavones was utilized to prepare chiral, nonracemic 3,4-chromanediones in high yields and enantioselectivities. These synthetic intermediates have been further elaborated to novel heterocyclic frameworks including angular pyrazines and dihydropyrazines. The absolute configuration of rearrangement products was initially determined by a nonempirical analysis of circular dichroism (CD) using time-dependent density functional theory (TDDFT) calculations and verified by X-ray crystallography of a hydrazone derivative. Initial studies of the mechanism support an intramolecular rearrangement pathway that may proceed through a benzopyrylium intermediate.

Synthesis and antioxidant properties of an unnatural plasmalogen analogue bearing a trans O-vinyl ether linkage

To assess the antioxidant behavior of trans-1, we first synthesized trans-allyl ether 4 by opening an (S)-glycidol derivative with an (E)-alk-2-en-ol, and then produced the unnatural E-enol ether 1 by a stereoselective iridium(I)-catalyzed olefin isomerization. Natural cis-1 was preferentially degraded by HOCl and was more protective than trans-1 against lipid peroxidation induced by a free-radical initiator, demonstrating that the geometry of the 1'-alkenyloxy bond participates in the antioxidant defensive role of 1.

Ruthenium hydride-catalyzed addition of aldehydes to dienes leading to beta,gamma-unsaturated ketones

An efficient cross-addition reaction of dienes with aldehydes was developed by using RuHCl(CO)(PPh3)3 as a catalyst to give a wide variety of beta,gamma-unsaturated ketones, where a pi-allylruthenium species, derived from hydroruthenation of diene, may be involved as a key intermediate.