Organosilicium-Chemie: Vom Molekül zum Werkstoff

Organosilicon Chemistry: From Molecules to Materials The transition from basic to applied organosilicon chemistry is described for the research fields that are studied by the author's group: silaethene chemistry, organosilicon polymer chemistry with silacycles and the chemistry of higher coordinated silicon species. Early investigations started with the study of the pyrolysis of silacyclobutanes that yielded silaethenes in the gas phase. However, these investigations are tedious and are of little use for a widespread study of silaethene chemistry. Therefore the generation of silaethenes in solution (from vinylchlorosilanes and tert-butyllithium) is the preferred method. Numerous differently substituted silaethenes have been generated in situ and their reactivity, especially in cycloaddition reactions, has been studied. Silaethenes that have two chlorine substituents at the silicon atom (especially Cl₂SiCHCH₂Bu^t) show an unusual cycloaddition reactivity and yield unexpected products with dienes and trienes (e. g. from [2+2] and [6+2] reactions); some of the silenes with donorfunctional groups at the α-C-atom undergo interesting intramolecular rearrangements. The cycloadducts of Si-dichlorofunctional silenes also show rearrangements when thermolyzed (e. g. [2+2] → [4+2] adducts). The reactivity of these silaethenes and their cyclo-adducts is due to the two chlorine atoms at the silicon atom and their influence can be explained by theoretical models. Silacycles synthesized from silaethenes have been incorporated or have been transformed into silicon containing polymers. Model compounds for nucleophilic substitution reactions at silicon centers and for the hydrolysis of chlorosilanes are higher coordinated silicon species up to coordination number „seven”︁. Some structures that describe such reactions have been characterized by X-ray crystallography.     

Use of carbon dioxide in industrial organic syntheses

Although carbon dixoide is important as an abundant carbonaceous raw material, so far, its utilization in chemical processes has been rather limited. This review covers the reactions of CO₂ employed in industry, such as the production of urea, the Kolbe-Schmitt reaction, the synthesis of cyclic organic carbonates and the use of CO₂ in methanol synthesis. Interesting recent developments in CO₂ chemistry, such as the reactions catalyzed by transition metals, are also described. Apart from the synthesis of polymers and hydrocarbons, the production of oxygen-containing substances appears to be very profitable and attractive for future industrial applications. Not only can derivatives of formic and carbonic acids be produced but also longer-chain carboxylic acids and their derivatives by reactions of carbon dioxide with hydrocarbons such as alkynes, alkenes and 1,3-dienes.     

Artificial Enzymes for Diels-Alder Reactions

The Diels-Alder (DA) reaction is a cycloaddition of a conjugated diene and an alkene (dienophile) leading to the formation of a cyclohexene derivative through a concerted mechanism. As DA reactions generally proceed with a high degree of regio- and stereoselectivity, they are widely used in synthetic organic chemistry. Considering eco-conscious public and governmental movements, efforts are now directed towards the development of synthetic processes that meet environmental concerns. Artificial enzymes, which can be developed to catalyze abiotic reactions, appear to be important synthetic tools in the synthetic biology field. This review describes the different strategies used to develop protein-based artificial enzymes for DA reactions, including for in cellulo approaches.     

Synthesis and Reactions of Aroyl Substituted Enone Mannich Salts

The classical Mannich reaction of aromatic methyl ketones with paraformaldehyde and dimethylamine hydrochloride resp. dimethyl(methylene)ammonium chloride has been extended to a few cases of 1‐aryl‐2‐dimethylaminomethyl‐prop‐2‐en‐1‐ones (ADMP reagents). They have gained remarkable attention in medicinal chemistry, but only more recently their properties as valuable building blocks for ring closure reactions to form either aroyl or dimethylaminomethyl substituted heterocyclic compounds has been evaluated. In this review, a collection of representative examples for their preparation (Scheme 2) and biological effects as well as the synthetic potential for the synthesis of heterocycles (Scheme 3—8) is given. The reaction of 4‐hydroxycoumarin delivers with ADMP reagents, via the formation of detectable 3‐(2‐benzoylallyl)‐4‐hydroxycoumarins as secondary substitution products, after ring closure 3‐benzoyl‐3,4‐dihy‐dro‐2H,5H‐1‐benzopyrano[4,3‐b]pyran‐5‐ones (Scheme 4). The reaction of 4‐hydroxy‐6‐methylpyran‐2‐one with ADMP reagents is investigated systematically in order to assess its suitability in carbon—carbon bond forming reactions as well as to provide the conditions for subsequent ring closure or intermolecular addition of further nucleophiles to the enone double bond of the intermediate 3‐(2‐benzoylallyl)‐4‐hy‐droxy‐6‐methylpyran‐2‐ones yielding miscellaneous 3‐substituted 2‐pyrones (Scheme 5 and 8), and their application as building blocks for the combinatorial chemistry. The condensation of ADMP reagents with 2‐aminopyridines gives rise to 3‐benzoyl‐3,4‐dihydro‐2H‐pyrido[1,2‐a]pyrimidines (Scheme 6) and the corresponding reaction using amidines affords 5‐benzoyl‐1,4,5,6‐tetrahydropyrimidines (Scheme 7).     

Design of a Multiuse Photoreactor To Enable Visible-Light Photocatalytic Chemical Transformations and Labeling in Live Cells

Despite the growing use of visible-light photochemistry in both chemistry and biology, no general low-heat photoreactor for use across these different disciplines exists. Herein, we describe the design and use of a standardized photoreactor for visible-light-driven activation and photocatalytic chemical transformations. Using this single benchtop photoreactor, we performed photoredox reactions across multiple visible light wavelengths, a high-throughput photocatalytic cross-coupling reaction, and in vitro labeling of proteins and live cells. Given the success of this reactor in all tested applications, we envision that this multi-use photoreactor will be widely used in biology, chemical biology, and medicinal chemistry settings.     

Catalytic Properties of the Antibody H11

The catalytic activity of the antibody H11 is shown to reside chiefly in its ability to hydrolyze 1-acetoxybutadiene to crotonaldehyde and to promote the cycloaddition of the intermediate enol with N-alkylmaleimides. This conclusion is based upon the demonstration that the enol tautomerizes too rapidly in solution to be a competent intermediate and that under the reaction conditions for H11, no cycloaddition occurs with crotonaldehyde and N-ethylmaleimide. As a first step towards a structural understanding of the chemistry of H11, chemical modification experiments have shown that reactions of acidic amino acids, tyrosine, lysine, and histidine, but not arginine, inhibit the reactions mediated by H11.     

Practical Synthesis of Allylic Silanes from Allylic Esters and Carbamates by Stereoselective Copper‐Catalyzed Allylic Substitution Reactions

The first copper‐catalyzed allylic substitution reactions of allylic acetates and carbamates employing a bis(triorganosilyl)zinc reagent are reported. This novel procedure avoids the use of stoichiometric amounts of copper salts which are usually mandatory with this chemistry. Application of this methodology to standard model substrates substantiates a high diastereoselectivity for the double bond geometry (E : Z) as well as the relative configuration (syn : anti).     

An Engineered Cholesterol Oxidase Catalyses Enantioselective Oxidation of Non-steroidal Secondary Alcohols

The enantioselective oxidation of 2° alcohols to ketones is an important reaction in synthetic chemistry, especially if it can be achieved using O₂-driven alcohol oxidases under mild reaction conditions. However to date, oxidation of secondary alcohols using alcohol oxidases has focused on activated benzylic or allylic substrates, with unactivated secondary alcohols showing poor activity. Here we show that cholesterol oxidase (EC 1.1.3.6) could be engineered for activity towards a range of aliphatic, cyclic, acyclic, allylic and benzylic secondary alcohols. Additionally, since the variants demonstrated high (S)-selectivity, deracemisation reactions were performed in the presence of ammonia borane to obtain enantiopure (R)-alcohols.     

Poly-para-xylelene: Its chemistry and application in coating technology

The chemistry of p-xylelene and of its analogues has been reviewed. Its modes of formation and polymerization to poly-p-xylelene have been described, and the initiation and hypothetical termination steps have been discussed. The reactions taking place in the gas phase and in the deposited film are contrasted with those taking place in solutions. The problems of crystallization of the polymer simultaneously proceeding with its growth have been stressed. Finally, the properties of poly-p-xylelenes and their application in the coating industry have been described in some detail, emphasizing the special advantages of gas-deposition leading directly to a solid and coherent film. Some future fields of application of this technique have been outlined.     

The Development of Visible-Light Photoredox Catalysis in Flow

Visible-light photoredox catalysis has recently emerged as a viable alternative for radical reactions otherwise carried out with tin and boron reagents. It has been recognized that by merging photoredox catalysis with flow chemistry, slow reaction times, lower yields, and safety concerns may be obviated. While flow reactors have been successfully applied to reactions carried out with UV light, only recent developments have demonstrated the same potential of flow reactors for the improvement of visible-light-mediated reactions. This review examines the initial and continuing development of visible-light-mediated photoredox flow chemistry by exemplifying the benefits of flow chemistry compared with conventional batch techniques.     

Sustainable functionalization and modification of materials via multicomponent reactions in water

In materials chemistry, green chemistry has established firm ground providing essential design criteria to develop advanced tools for efficient functionalization and modification of materials. Particularly, the combination of multicomponent reactions in water and aqueous media with materials chemistry unlocks a new sustainable way for constructing multi-functionalized structures with unique features, playing significant roles in the plethora of applications. Multicomponent reactions have received significant consideration from the community of material chemistry because of their great efficiency, simple operations, intrinsic molecular diversity, and an atom and a pot economy. Also, by rational design of multicomponent reactions in water and aqueous media, the performance of some multicomponent reactions could be enhanced by the contributing “natural” form of water-soluble materials, the exclusive solvating features of water, and simple separating and recovering materials. To date, there is no exclusive review to report the sustainable functionalization and modification of materials in water. This critical review highlights the utility of various kinds of multicomponent reactions in water and aqueous media as green methods for functionalization and modification of siliceous, magnetic, and carbonaceous materials, oligosaccharides, polysaccharides, peptides, proteins, and synthetic polymers. The detailed discussion of synthetic procedures, properties, and related applicability of each functionalized/modified material is fully deliberated in this review.     

Bureau of Commercial Fisheries Oil Research program

Summary The Bureau of Commercial Fisheries has had under way since 1955 an extensive research program to develop wider uses for fish oils. The program is carried out in the Bureau’s own laboratories, in university laboratories, and in other qualified laboratories. The initial effort has been concentrated largely on basic research in an effort to learn more about the chemistry of fish oils, a field heretofore incompletely explored. Some applied research projects also were begun concurrently. Basic studies are being carried out on the chemistry of the components of fish oils (for example, polyene fatty acids), on the extracted fish oils themselves, and onin situ fish oils of the fish tissue. Investigations of fish-oil fatty acids are being made on chemical structure, methods of separation, chemical reactions, oxidative deterioration, and nutritive value, with especial emphasis on possible therapeutic aspects for human beings. The applied research projects include investigation of fish oils and the chemically modified compounds thereof as fungicides, as leather lubricants, and as ore-flotation agents. The applied and basic programs are coordinated so that findings of the basic work can be put to use in the applied work as soon as available.     

A Versatile Synthetic Platform Based on Bicyclo[4.1.0]heptenes

Bicyclo[4.1.0]heptenes, which are readily accessible molecules via the transition metal-catalyzed cycloisomerization of 1,6-enynes, and have served as useful building blocks in organic synthesis. These molecules can undergo a variety of ring-opening reactions given that the release of the cyclopropyl ring strain (27.5 kcal/mol) may serve as a thermodynamic driving force for reactions, and the double bond within the skeleton can afford the kinetic opportunity to initiate the ring-opening via a coordination to a metal species. Even though the chemistry of the cyclopropyl group has been widely explored in organic chemistry, less attention has been paid to the chemistry of bicyclo[4.1.0]heptenes. However, during the past 5 years, we have been engaged in the exploration of the chemistry of bicyclo[4.1.0]heptenes. This review describes the chemistry developed in our laboratory. Depending upon the position, number, and identity of the substituent(s), the identity of the tether group, and the nature of the catalytic system, bicyclo[4.1.0]heptenes can undergo a variety of transformations. Our studies have revealed the reaction patterns of bicyclo[4.1.0]heptenes which include thermal reactions, nucleophilic addition, and rhodium-catalyzed reactions, that can proceed both with and without opening of the cyclopropyl ring. The chemistry described in this review can be used to produce a variety of new compounds such as 2,4-pentadienals, 3-methylene-4-vinylcyclohex-1-enes, bicyclo[3.2.2]nonadienes, 1,6,7,9a-tetrahydrocyclohepta[c] pyrans and -pyridines, hexahydroisoquinolines, 4-oxa-6-azatricyclo[3.3.0.0^2,8]octanes, and heterotricyclo[3.3.1.0^2,8]nonanes.     

New synthetic strategy for facile synthesis of functional polymers by one‐pot combination of controlled radical polymerization and enzymatic reaction

One‐pot synthesis in organic chemistry is deeply rooted in people's minds due to its huge improvement in efficiency compared with conventional stepwise synthesis. Nowadays, such a concept has also been shifted to polymer chemistry by one‐pot introducing compatible or orthogonal organic reactions with polymerizations for facilely synthesizing or modifying polymers. This review systematically summarizes recent developments in the one‐pot combination of enzymatic reactions with controlled radical polymerization to prepare functional polymers. © 2015 Society of Chemical Industry     

Advances and Challenges in the Synthesis of Poly(p-phenylene vinylene)-Based Polymers

We provide an overview of the current progress in the synthesis of poly(p-phenylene vinylene) (PPV) polymers. The described synthetic approaches can be divided into four main categories: polymerization of quinodimethane intermediates, metathesis polymerization, nucleophilic polycondensation, and palladium-catalyzed cross-coupling. While such variety is remarkable and very high-molecular-weight PPV can be prepared by some methods, the synthetic chemistry of PPV still limits the structural variety and purity of arylene vinylene polymers. In particular, palladium-catalyzed cross-coupling reactions, the method of choice in the contemporary conjugated polymer chemistry, often shows limited success in PPV series. On the other hand, the possibility of using metathesis polymerization creates new opportunities not available for other classes of conjugated polymers.     

Tetrazine-Triggered Release of Carboxylic-Acid-Containing Molecules for Activation of an Anti-inflammatory Drug

In addition to its use for the study of biomolecules in living systems, bioorthogonal chemistry has emerged as a promising strategy to enable protein or drug activation in a spatially and temporally controlled manner. This study demonstrates the application of a bioorthogonal inverse electron-demand Diels–Alder (iEDDA) reaction to cleave trans-cyclooctene (TCO) and vinyl protecting groups from carboxylic acid-containing molecules. The tetrazine-mediated decaging reaction proceeded under biocompatible conditions with fast reaction kinetics (<2 min). The anti-inflammatory activity of ketoprofen was successfully reinstated after decaging of the nontoxic TCOprodrug in live macrophages. Overall, this work expands the scope of functional groups and the application of decaging reactions to a new class of drugs.     

Metathesis as a versatile tool in oleochemistry

Olefin metathesis, awarded with the Nobel Prize in Chemistry 2005 for Chauvin, Grubbs and Schrock, has emerged as a powerful tool for organic as well as polymer chemistry. In oleochemistry, this reaction is well known and has been applied for many decades. Examples include the functionalization of the double bonds of different oleochemicals or the (direct) polymerization of plant oils via metathesis. More recent developments, particularly the development of better and more robust catalysts, allow for highly efficient cross‐metathesis reactions opening new possibilities for the direct introduction of chemical functionalities. Within this contribution, the development of metathesis in oleochemistry will be discussed, covering self‐metathesis as well as more recent developments in the field of cross‐metathesis that lead to desired platform chemicals.     

Remarkable Efficiency Improvement in the Preparation of Insoluble Polymer‐Bound (IPB) Enantioselective Catalytic Systems by the Use of Silicone Chemistry

The use of platinum‐catalyzed hydrosilylation chemistry of silicones greatly simplifies the preparation of bis‐oxazoline (box) ligands covalently bound to an insoluble polymeric support. The use of such immobilized chiral ligands in different copper‐catalyzed asymmetric transformations (carbonyl‐ene, Mukaiyama aldol and olefin cyclopropanation reactions) allows the attainment of high levels of enantioselectivity (91–99 % ee).     

Recent advances in synthetic transformations mediated by cerium(IV) ammonium nitrate

Cerium(IV) ammonium nitrate (CAN) has recently emerged as a versatile reagent for oxidative electron transfer; the overwhelming number of reports serve as a testimony to the unparalleled utility of CAN in a variety of transformations of synthetic importance. Our recent work has uncovered novel carbon-carbon bond-forming reactions leading to the one-pot synthesis of dihydrofurans, tetrahydrofurans, and aminotetralins. In addition, we have developed a number of facile carbon-heteroatom bond-forming reactions by the CAN-mediated oxidative addition of soft anions to alkenes. A mechanistic rationale has been provided for the reactions explored. As might be expected of very powerful one-electron oxidants, the chemistry of cerium(IV) oxidation of organic molecules is dominated by radical and radical cation chemistry.