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Matrix photolysis and flash vacuum pyrolysis (FVP) from four different precursors yields acetylketene. The infrared spectra of the conformers produced are identified by matrix isolation of the infrared spectroscopy. The acetylketene conformers are found to have equal energy and a rotational barrier of ca. 39 kilojoules per mole.

Neutralization-reionization mass spectrometric studies reveal that (methylimino)ethenethione and iminoethane-thione radical cations are stable on the microsecond time scale. The imino-radical cation tautomerizes to H-CS-CN on generation from isoxazolones. Ab initio G2(MP2) level-based calculations yield the structures and stabilities of the two radical cations. Predicted IR and UV spectra and ionization energies of both radical cations agree well with experimental data.

A study was made on the preparative and mechanistic aspects of the formation of simple mono- and bifunctionalized trioxabicyclononadienes. The methods entailed the addition of nucleophiles to alpha-oxoketene 5 following a multistep reaction sequence. The results indicated the viability of the methods which permit the synthesis of several varieties of mono- and bifunctionalized derivatives as opposed to previous approaches which showed limited synthetic value.

Dipivaloylketene dimerization in several polar and nonpolar media leads to the formation of the (2 + 4) dimer while in dimethyl sulfoxide pyridine or tributylphosphine, dimerization takes place at the C=O bond leading to the formation of a dioxinone. The latter dimerization reaction is a new type of alpha-oxo ketene dimerization. Cycloaddition reactions of dipivaloylketene with a number of compounds reveal that dipivaloylketene undergoes both (2 + 4) and (2 + 2) addition the general aspects of which are discussed.

Oxidative functionalization of alkenes is a versatile strategy for the preparation of many oxygen-containing scaffolds, such as epoxides, diols, or carbonylcontaining compounds. In addition to conventional chemical methods, which rely on the utilization of stoichiometric amounts of oxidizing reagents, some electrochemical procedures have been developed to achieve these transformations. Typical electrochemical procedures employ tailored and often complex redox mediators to achieve the target transformation. Herein we present a modular approach for the synthesis of epoxides, diols, and aldehydes from a single set of reaction components. With sodium bromide as an inexpensive electrocatalyst and water as the oxygen donor, the outcome of the reaction (epoxide, 1,2-diol, or aldehyde) can be selected by simply tuning the electrolysis conditions. This convenient platform has been accomplished by developing a selective one-pot three-step bromide-electrocatalyzed epoxidation/ring opening/carboncarbon cleavage sequence. Its modularity permits the selection of the desired product, as the sequential reaction can be ended when the target compound has been formed. Themethod has been applied to a diversely functionalized terminal and non-terminal olefins. [ABSTRACT FROM AUTHOR]

Introduction of acetoxy groups to organic molecules is important for the preparation of many active ingredients and synthetic intermediates. A commonly used and attractive strategy is the oxidative decarboxylation of aliphatic carboxylic acids, which entails the generation of a new C(sp3)–O bond. This reaction has been traditionally carried out using excess amounts of harmful lead(IV) acetate. A sustainable alternative to stoichiometric oxidants is the Hofer-Moest reaction, which relies on the 2-electron anodic oxidation of the carboxylic acid. However, examples showing electrochemical acetoxylation of amino acids are scarce. Herein we present a general and scalable procedure for the anodic decarboxylative acetoxylation of amino acids in batch and continuous flow mode. The procedure has been applied to the derivatization of several natural and synthetic amino acids, including key intermediates for the synthesis of active pharmaceutical ingredients. Good to excellent yields were obtained in all cases. Transfer of the process from batch to a continuous flow cell signficantly increased the reaction throughput and space–time yield, with excellent product yields obtained even in a single-pass. The sustainability of the electrochemical protocol has been examined by evaluating its green metrics. Comparison with the conventional method demonstrates that an electrochemical approach has a significant positive effect on the greenness of the process. [ABSTRACT FROM AUTHOR]

Strained compounds are privileged moieties in modern synthesis. In this context, 1‐azabicyclo[1.1.0]butanes are appealing structural motifs that can be employed as click reagents or precursors to azetidines. We herein report the first telescoped continuous flow protocol for the generation, lithiation, and electrophilic trapping of 1‐azabicyclo[1.1.0]butanes. The flow method allows for exquisite control of the reaction parameters, and the process operates at higher temperatures and safer conditions with respect to batch mode. The efficiency of this intramolecular cyclization/C3‐lithiation/electrophilic quenching flow sequence is documented with more than 20 examples. [ABSTRACT FROM AUTHOR]

Oscillatory flow reactors (OFRs) superimpose an oscillatory flow to the net movement through a flow reactor. OFRs have been engineered to enable improved mixing, excellent heat- and mass transfer and good plug flow character under a broad range of operating conditions. Such features render these reactors appealing, since they are suitable for reactions that require long residence times, improved mass transfer (such as in biphasic liquid-liquid systems) or to homogeneously suspend solid particles. Various OFR configurations, offering specific features, have been developed over the past two decades, with significant progress still being made. This review outlines the principles and recent advances in OFR technology and overviews the synthetic applications of OFRs for liquid-liquid and solid-liquid biphasic systems. [ABSTRACT FROM AUTHOR]

The recent renaissance of electrochemical methods for organic synthesis has also attracted increased interest towards flow electrochemistry as the most suitable scale-up strategy. Many electrochemical methods using flow cells are based on recirculation of the electrolyte solution. However, single-pass processing is very attractive as it permits integration of the electrochemical reaction with other synthetic or purification steps in a continuous stream. Translation of batch electrochemical procedures to single-pass continuous flow cells can be challenging to beginners in the field. Using the electrochemical methoxylation of 4-methylanisole as model, this paper provides newcomers to the field with an overview of the factors that need to be considered to develop a flow electrochemical process, including advantages and disadvantages of operating in galvanostatic and potentiostatic mode in small scale reactions, and the effect of the interelectrode gap, supporting electrolyte concentration and pressure on the reaction performance. A comparison of the reaction efficiency in batch and flow is also presented. [ABSTRACT FROM AUTHOR]

The detailed development of photochemical benzylic brominations using a NaBrO3/HBr bromine generator in continuous flow mode is reported. Optimization of the bromine generator enables highly efficient mass utilization by HBr recycling, coupled with fast interphase transfer within a microstructured photochemical reactor (405 nm LEDs). Intensification of the reaction system, including complete removal of organic solvent, allowed a reduction in PMI from 13.25 to just 4.33. The photochemical transformation achieved exceptionally high throughput, providing complete conversion in residence times as low as 15 s. The organic solvent-free preparation of two pharmaceutically relevant building blocks was demonstrated with outstanding mass efficiency, by monobromination (1.17 kg scale in 230 min, PMI = 3.08) or dibromination (15 g scale in 20 min, PMI = 3.64). [ABSTRACT FROM AUTHOR]