The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.

Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations.

2.6.4. Other Carbohydrate-Based Catalysts 3976 2.7. Carbocyclic Ketones 3977 2.8. Ketones with an Attached Chiral Moiety 3979 3. Chiral Iminium Salt-Catalyzed Epoxidation 3979 3.

Organocatalytic Oxidation. Asymmetric Epoxidation of Olefins Catalyzed by Chiral Ketones and Iminium Salts

The four-membered oxetane ring has been increasingly exploited for its contrasting behaviors: its influence on physicochemical properties as a stable motif in medicinal chemistry and its propensity to undergo ring-opening reactions as a synthetic intermediate. These applications have driven numerous studies into the synthesis of new oxetane derivatives. This review takes an overview of the literature for the synthesis of oxetane derivatives, concentrating on advances in the last five years up to the end of 2015. These methods are clustered by strategies for preparation of the ring and further derivatization of preformed oxetane-containing building blocks. Examples of the use of oxetanes in medicinal chemistry are reported, including a collation of oxetane derivatives appearing in recent patents for medicinal chemistry applications. Finally, examples of oxetane derivatives in ring-opening and ring-expansion reactions are described.

/pdf/oxetanes-recent-advances-in-synthesis-reactivity-and-3v6yf8rtvd.pdf

Oxetanes: Recent Advances in Synthesis, Reactivity, and Medicinal Chemistry

An overview is given on pesticide-residue determination in environmental and food samples by liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). Pesticides comprise a large number of substances that belong to many completely different chemical groups, the only common characteristic is that they are effective against pests. They still constitute a challenge in MS because there is no collective pathway for fragmentation. A brief introduction to the theory of tandem MS permits a discussion of which parameters influence the ionization efficiency when the ions are subjected to different actions. Emphasis is placed on the different tandem MS instruments: triple and ion-trap quadrupoles, and hybrid quadrupole time-of-flight (Q-TOF), including advantages and drawbacks, typical detection limits, and ion signals at low concentrations. The instrumental setup, as well as LC and mass spectrometric experimental conditions, must be carefully selected to increase the performance of the analytical system. The capacity of each instrument to provide useful data for the identification of pesticides, and the possibility to obtain structural information for the identification of target and non-target compounds, are discussed. Finally, sample preparation techniques and examples of applications are debated to reveal the potential of the current state-of-the-art technology, and to further promote the usefulness of tandem MS.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mas.10071

Environmental and food applications of LC-tandem mass spectrometry in pesticide-residue analysis: an overview.

Singlet-oxygen chemiluminescence in peroxide reactions.

The photochemical degradation of the herbicides alachlor (2-chloro-2′,6′-diethyl-N-methoxymethylacetanilide) and bentazone (3-isopropyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide) in distilled water and in river water, under xenon arc lamp irradiation, was investigated. Analytical determinations were carried out by using a xenon arc photoreactor and online solid-phase extraction coupled to liquid-chromatography diode-array and liquid-chromatography mass-spectrometry detection systems. Photolysis experiments were performed at low concentration (20 μg/L), and the advantages of this methodology over conventional techniques are discussed. The photodegradation of alachlor and bentazone is a process depending on the water type, humic substances, and pH. When using a solution of 4 mg/L of humic matter, the estimated alachlor and bentazone half-lives were 84 and 150 min, respectively, using a total irradiance of 550 W/m2 in the range of 300 to 800 nm. The degradation of alachlor and bentazone followed pseudo second- and first-order kinetics, respectively. The major photodegradation products of both herbicides were identified either by on-line solid-phase extraction (SPE)-liquid chromatography-thermospray mass spectrometry (LC/TSP-MS) or on-line-SPE-LC/TSP-tandem mass spectrometry (LC/TSP-MS/MS). In addition to that, a total of six transformation products of alachlor were synthesized in our laboratory and their MS spectra were compared with those of the breakdown products obtained. After photodegradation, a total of 14 photoproducts resulted from alachlor dechlorination with subsequent hydroxylation and cyclization processes. The two major photoproducts were identified as hydroxy-alachlor and 8-ethyl-1-methoxymethyl-4-methyl-2-oxo-1,2,3,4-tetrahydroquinone. No significant breakdown products of bentazone could be identified.

Comparative photodegradation rates of alachlor and bentazone in natural water and determination of breakdown products

On the preparation of amine N-oxides by using dioxiranes

Availability and reactivity of concentrated dimethyldioxirane solutions in solvents other than acetone

Easy availability of more concentrated and versatile dimethyldioxirane solutions

A neat and high yield chemoselective epoxidation of alkene moieties present in tertiary amines is accomplished by treatment of the corresponding amine–boron trifluoride adduct with dimethyldioxirane or methyl(trifluoromethyl)dioxirane.

Marta Ferrer

Papers

Comparative photodegradation rates of alachlor and bentazone in natural water and determination of breakdown products

On the preparation of amine N-oxides by using dioxiranes

Availability and reactivity of concentrated dimethyldioxirane solutions in solvents other than acetone

Easy availability of more concentrated and versatile dimethyldioxirane solutions

Use of dioxiranes for the chemoselective oxidation of tertiary amines bearing alkene moieties