1,2-cyclic sulfamidates as versatile precursors to thiomorpholines and piperazines

[reaction: see text] 1,2-Cyclic sulfamidates undergo regiospecific nucleophilic displacement with either methyl thioglycolate or alpha-amino esters, followed by lactamization (thermal, base-mediated, or cyanide-catalyzed), to give thiomorpholin-3-ones and piperazin-2-ones.     

Peroxyesters as precursors to peroxyl radical clocks

The reactions of peroxyl radicals are at the center of the oxidative degradation of essentially all petroleum-derived hydrocarbons and biological lipids and consequently, the inhibition of these processes by radical-trapping antioxidants. Recently described peroxyl radical clocks offer a simple, convenient, and inexpensive method of determining rate constants for H-atom transfer reactions to peroxyl radicals, greatly enabling the kinetic and mechanistic characterization of compounds with antioxidant properties. We follow up our preliminary communication on the development of a methodology utilizing tert-butyl styrylperacetate as a precursor to a versatile peroxyl radical clock with the present paper, wherein we describe a novel naphthyl analogue, which provides for much improved product resolution for analysis, and provide the complete details associated with its development and application. Using this new precursor, and with consideration of the expanded set of reaction products, inhibition rate constants were measured for a variety of representative phenolic and diarylamine radical-trapping antioxidants. We also provide details for the use of this methodology for the determination of mechanistic information, such as kinetic solvent effects, Arrhenius parameters, and kinetic isotope effects.     

Rhodium carbene complexes as versatile catalyst precursors for Si-H bond activation

Rhodium(III) complexes comprising monoanionic C,C,C-tridentate dicarbene ligands activate Si-H bonds and catalyse the hydrolysis of hydrosilanes to form silanols and siloxanes with concomitant release of H(2). In dry MeNO(2), selective formation of siloxanes takes place, while changing conditions to wet THF produces silanols exclusively. Silyl ethers are formed when ROH is used as substrate, thus providing a mild route towards the protection of alcohols with H(2) as the only by-product. With alkynes, comparably fast hydrosilylation takes place, while carbonyl groups are unaffected. Further expansion of the Si-H bond activation to dihydrosilanes afforded silicones and polysilyl ethers. Mechanistic investigations using deuterated silane revealed deuterium incorporation into the abnormal carbene ligand and thus suggests a ligand-assisted mechanism involving heterolytic Si-H bond cleavage.     

Precipitation as a simple and versatile method for preparation of optical nanochemosensors

Optical nanosensors for such important analytes as oxygen, pH, temperature, etc. are manufactured in a simple way via precipitation. Lipophilic indicators are entrapped into nanobeads based on poly(methyl methacrylate), polystyrene, polyurethanes, ethylcellulose, and other polymers. Charged groups greatly facilitate formation of the small beads and increase their stability. Sensing properties of the beads can be tuned by choosing the appropriate indicator. Nanosensors for carbon dioxide and ammonia are found to be cross-sensitive to pH if dispersed in aqueous media. These nanobeads are successfully employed to design bulk optodes. Nanochemosensors with enhanced brightness via light-harvesting and multi-functional magnetic nanosensors also are prepared.     

3H-benzophosphepine complexes: versatile phosphinidene precursors

The synthesis of a variety of benzophosphepine complexes [R = Ph, t-Bu, Me; ML(n )()= W(CO)(5), Mo(CO)(5), Cr(CO)(5), Mn(CO)(2)Cp] by two successive hydrophosphinations of 1,2-diethynylbenzene is discussed in detail. The first hydrophosphination step proceeds at ambient temperature without additional promoters, and subsequent addition of base allows full conversion to benzophosphepines. Novel benzeno-1,4-diphosphinanes were isolated as side products. The benzophosphepine complexes themselves serve as convenient phosphinidene precursors at elevated, substituent-dependent temperatures (>55 degrees C). Kinetic and computational analyses support the proposal that the phosphepine-phosphanorcaradiene isomerization is the rate-determining step. In the absence of substrate, addition of the transient phosphinidene to another benzophosphepine molecule is observed, and addition to 1,2-diethynylbenzene furnishes a delicate bidentate diphosphirene complex.     

Glycol-modified silanes as versatile precursors in the synthesis of thin periodically organized silica films

Optically transparent, hexagonally organized mesoporous silica films with variable thickness have been synthesized from aqueous solutions of tetrakis(2-hydroxyethyl)orthosilicate (EGMS) in the presence of an amphiphilic structure-directing agent (Pluronic P123). Two different methods for film formation have been compared: spin coating from a highly concentrated and viscous precursor solution comprising EGMS, P123 and water/HCl via a direct templating of a preformed LC phase and spin coating from diluted solutions in tetrahydrofuran, thus following a cooperative self-organization process induced by solvent-evaporation. The influence of processing parameters such as pH-value, concentration of the precursors as well as aging of the sol on the periodic mesostructure is investigated.     

Laser flash photolysis studies of alkoxyl radical kinetics using 4-nitrobenzenesulfenate esters as radical precursors

4-Nitrobenzenesulfenate esters were used as precursors for the generation of alkoxyl radicals under laser flash photolysis conditions. The esters were efficiently cleaved using the Nd:YAG third harmonic (355 nm) to produce alkoxyl radicals and the 4-nitrobenzenethiyl radical. Rate constants for beta-scission and 1, 5-hydrogen abstraction reactions of alkoxyl radicals were measured.     

Evaluation of phenylorganotellurium compounds as radical precursors in dialkylzinc-mediated radical addition to CN double bonds

Diethylzinc-mediated radical addition to CN bonds was investigated in the presence of phenylorganotellurium compounds as radical precursors. As group transfer agents, secondary alkyl phenyl tellurides were shown to be about twice as reactive as the corresponding alkyl iodides towards ethyl radical. Their use was proven to be advantageous regarding both chemoselectivity and yield. The replacement of diethylzinc by dimethylzinc, offers no advantage in these reactions.     

2,3-unsubstituted chromones and their enaminone precursors as versatile reagents for the synthesis of fused pyridines

A divergent and regioselective approach to fused pyridines was developed through formal [3 + 3] cyclocondensations from simple 2,3-unsubstituted chromones or their enaminone precursors.     

Visible-light-driven cyanoalkylation of quinoxalinones using cyclobutanone oxime esters as the radical precursors

We have developed a versatile visible-light-driven cyanoalkylation of quinoxalinones under mild conditions. First, the cyanoalkyl radicals are generated from readily available cyclobutanone oxime esters under blue light irradiation. Then the generated radicals react with heterocycles such as quinoxalinones to give the final cyanoalkylation products. The protocol tolerates a wide range of functional groups. Our cyanoalkylation protocol does not need cyanide-based reagents and also does not need external oxidants.     

A simple and versatile route to ketomethylene dipeptide analogs

A facile and versatile procedure for the synthesis of ketomethylene dipeptides by using N^α-Z-amino acid halomethyl ketones and dimethyl malonate as starting materials is reported. By application of this method, alanyl and phenylalanyl derivatives containing C-terminal Gly, Ala, Asp, Phe and Trp residues have been prepared.     

Highly versatile organostibine mediators for living radical polymerization

A new versatile method for conducting living radical polymerization has been developed in which organostibines induce consecutive group-transfer radical reactions with alkenes. The method has been successfully applied, for the first time, to the controlled polymerization of both conjugated and unconjugated vinyl monomers, and the desired polymers with predetermined molecular weight and low polydispersity index were obtained in excellent yields. This characteristic feature of this method is exemplified in the first synthesis of block copolymers composed of conjugated and unconjugated monomers, which would be of great importance as functional smart organic nanomaterials.     

Cyclic sulfamidates as versatile lactam precursors. An evaluation of synthetic strategies towards (-)-aphanorphine

A full account of studies which led to the efficient asymmetric synthesis of (-)-aphanorphine is reported. Two routes to the key cyclic sulfamidate intermediate are described, the first was based on a chiral auxiliary approach and the second utilised asymmetric hydrogenation methodology. A range of C(3)-substituted lactams (, and ) were synthesised and evaluated as precursors for Pd(0) catalysed entries (based on (i) alpha-arylation of a lactam enolate and (ii) reductive Heck reaction) to the 3-benzazepine core of . These approaches were less effective than an aryl radical cyclisation which allowed the completion of a synthesis of in 12 steps from anisaldehyde.     

Photo-pens: a simple and versatile tool for maskless photolithography

We demonstrate conical pores etched in tracked glass chips for fabricating patterns at the micrometer scale. Highly fluorescent patterns based on photopolymerization of diacetylene films were formed by irradiating UV light through conical pores called "photo-pens". The properties of photopens were investigated through experiments, finite-difference-time-domain (FDTD) simulations and numerical calculations based on Fresnel equations. We show that the pattern dimensions are easily controlled by adjusting the exposure time. Thus, patterns with a range of dimensions can be fabricated without any need of changes in the pore diameter. Parallel patterning was also demonstrated by simultaneously exposing the films to photons through multiple pores in the chip. Our method provides an inexpensive, versatile, and efficient way for patterning without the use of sophisticated masks.     

2-nitro thioglycoside donors: versatile precursors of beta-D-glycosides of aminosugars

2-Nitro thioglycosides can be prepared by the Michael addition of thiophenol to 2-nitroglycal derivatives. NIS/TMSOTf activation of these 2-nitro thioglycosides, in the presence of alcohols, rapidly and cleanly led to the desired glycosides in good yield and beta-selectivity. Reduction of the nitro group allowed generation of the corresponding 2-acetamido glycosides.     

A simple and versatile PSA system for heavy metal determinations

An easy to build potentiometric stripping analysis system for heavy metal determinations (Zn, Cd, Pb, Cu) is described which reaches good sensitivity and precision. Main components are an IBM compatible computer, an ADDA-conversion card and two selfmade electrodes, so it can be realized for one tenth of the price of complete commercial systems. A graphite pencil lead covered with a Hg-film is used as working electrode and a Ag/AgCl electrode as a combined reference/counter electrode. Reproducibility and calibration measurements are reported, heavy metal determinations on soil samples are compared with AAS results.