Catalytic oxidative cleavage of terminal olefins by chromium(III) stearate

A new synthetic methodology for the preparation of carbonyl compounds from the oxidative cleavage of terminal olefins has been developed. With the use of TBHP in combination with chromium(III) stearate, selective oxidation of double bonds conjugated with aromatic ring or carbonyl group could be achieved at ambient temperature in moderate to excellent yield. The oxidative cleavage of electron rich -methylstyrene derivatives proceeded in good to excellent yield whereas lower yields were observed in -methylstyrene derivatives containing an electron withdrawing group. This developed oxidation reaction was believed to undergo via free radical process and high valent chromium oxo species.     

Synthesis of isomeric fluoronitrobenzene-sulfonyl chlorides

The synthesis of five hitherto unknown isomeric fluoronitrobenzenesulfonyl chlorides is described. The compounds are prepared from difluoronitrobenzenes by a two-step procedure. In the first step the starting compounds undergo a regioselective reaction with phenylmethanethiol giving rise to the corresponding thioethers. The oxidative cleavage of the latter with chlorine results in the sulfonyl chlorides in good yields. One example of a threefold sequential functionalization of 2-fluoro-6-nitrobenzenesulfonyl chloride showing the synthetic utility of the title compounds is provided.     

Synthesis of Naphtho[1,8‐bc]pyran Derivatives and Related Compounds through Hydroxy Group Directed C?H Bond Cleavage under Rhodium Catalysis

The straightforward and efficient synthesis of naphtho[1,8‐bc]pyran derivatives and related polycyclic compounds is achieved by the rhodium‐catalyzed oxidative coupling of 1‐naphthols or other phenolic and alcoholic substrates with alkynes. In these annulation reactions, the hydroxy groups effectively act as the key function for the regioselective C? H bond cleavage.     

Cobalt(II) Porphyrin‐Catalyzed Intramolecular Cyclopropanation of N‐Alkyl Indoles/Pyrroles with Alkylcarbene: Efficient Synthesis of Polycyclic N‐Heterocycles

A protocol on chemoselective cobalt(II) porphyrin‐catalyzed intramolecular cyclopropanation of N‐alkyl indoles/pyrroles with alkylcarbenes has been developed. The reaction enables the rapid construction of a range of nitrogen‐containing polycyclic compounds in moderate to high yields from readily accessible materials. These N‐containing polycyclic compounds can be converted into a variety of N‐heterocycles with potential synthetic and biological interest. Compared to their N‐tosylhydrazone counterparts, the use of bulky N‐2,4,6‐triisopropylbenzenesulfonyl hydrazones as carbene precursors allows cyclopropanation to occur under milder reaction conditions.     

Synthesis of Fluorine‐Containing Multisubstituted Phenanthridines by Rhodium‐Catalyzed Alkyne [2+2+2] Cycloaddition and Tandem sp2 C?H Difluoromethylenation

A highly efficient method for the synthesis of fluorine‐containing multisubstituted phenanthridines through Rh‐catalyzed alkyne [2+2+2] cycloaddition reactions has been developed. This method exhibits excellent functional‐group compatibility. When a bromodifluoromethyl group, rather than a trifluoromethyl group, was employed in the cycloaddition reaction, more‐complicated polycyclic compounds were obtained through tandem Rh‐catalyzed cycloaddition/C? H difluoromethylenation. This route provides convenient access to fluorine‐containing polycyclic compounds.     

Cleavage of oximes using a solid supported hypervalent organoiodine reagent

A facile and efficient oxidative cleavage of oximes to form carbonyl compounds is reported using phenyl iodonium (III) diacetate (PIDA) and polymer supported polydiacetoxyiodostyrene. Regeneration of carbonyl compounds from corresponding oximes is an important reaction, since oxime derivatives constitute one of the primary methods for purification and characterization of carbonyl compounds. This process overcomes many of the disadvantages associated with other oxidative methods such as long reaction times, difficulties in isolation of products and formation of over oxidized products.     

Total syntheses of bioactive oxidized ethanolamine phospholipids

[reaction: see text] Truncated ethanolamine phospholipids containing aldehyde functionality, e.g. OVPE, and the corresponding acids, are generated by oxidative cleavage of polyunsaturated phospholipids. To confirm their identities and facilitate studies of the chemistry and biological actions of these analogues of biologically active phosphatidylcholines, e.g. OVPC, total syntheses were developed. An efficient general strategy was used that features selective N-protection of 2-lysophosphatidylethanolamine, and generation of the target compounds by mild deprotection of stable precursors.     

Synthesis of Nitrogen‐Containing Polyaromatics by Aza‐Annulative π‐Extension of Unfunctionalized Aromatics

Nitrogen‐containing polycyclic aromatic compounds (N‐PACs) are an important class of compounds in materials science. Reported here is a new aza‐annulative π‐extension (aza‐APEX) reaction that allows rapid access to a range of N‐PACs in 11–84 % yields from readily available unfunctionalized aromatics and imidoyl chlorides. In the presence of silver hexafluorophosphate, arenes and imidoyl chlorides couple in a regioselective fashion. The follow‐up oxidative treatment with p‐chloranil affords structurally diverse N‐PACs, which are very difficult to synthesize. DFT calculations reveal that the aza‐APEX reaction proceeds through the formal [4+2] cycloaddition of an arene and an in situ generated diarylnitrilium salt, with sequential aromatizations having relatively low activation energies. Transformation of N‐PACs into nitrogen‐doped nanographenes and their photophysical properties are also described.     

Iron(II)‐Catalyzed Direct Cyanation of Arenes with Aryl(cyano)iodonium Triflates

A direct oxidative cyanation of arenes under Fe^II catalysis with 3,5‐di(trifluoromethyl)phenyl(cyano)iodonium triflate (DFCT) as the cyanating agent has been developed. The reaction is applicable to wide range of aromatic substrates, including polycyclic structures and heteroaromatic compounds.     

Why are olefins oxidized by RuO4 under cleavage of the carbon-carbon bond whereas oxidation by OsO4 yields cis-diols?

Quantum chemical calculations using gradient-corrected (B3LYP) density functional theory have been carried out to investigate the mechanism of the oxidative cleavage of alkenes by ruthenium tetraoxide. The initial reaction of the tetraoxide with the olefin occurs via a [3+2] cycloaddition as in the case of osmium tetraoxide. The results clearly show that the bond cleavage does not take place at the primary adduct, but much later in the reaction path. After the formation of the ruthenium(VI)dioxo-2,5-dioxolane, the reaction proceeds with the addition of a second olefin to yield ruthenium(IV)-bis(2,5-dioxolane), which in turn becomes oxidized first to rutheniumoxo(VI)-bis(2,5-dioxolane) 6(Ru) and then to ruthenium(VIII)-dioxo-bis(2,5-dioxolane) 7(Ru). Only in complexes containing the metal center in the formal oxidation state +VIII are low activation barriers for C-C bond cleavage and exothermic formation of carbonyl compounds as products calculated. The lowest activation barrier, DeltaH(++) = 2.5 kcal/mol, is calculated for the C-C bond breaking reaction of 7(Ru) which is predicted as the pivotal intermediate of the oxidation reaction. The calculations of the oxidation reaction with OsO(4) show that those reactions where the oxidation state of the metal increases have larger activation barriers for M = Ru than for M = Os, while reactions which reduce the oxidation state have a lower activation barrier for ruthenium compounds. Also, reactions which increase the oxidation state of the metal are in the case of M = Os more exothermic than for M = Ru. In this work, all important points of the potential energy surface (PES) are reported, and the complete catalytic cycle for the oxidative cleavage of olefins by ruthenium tetraoxide is presented.     

Rhodium-Catalyzed C,C-Double Bond Cleavage by Molecular Oxygen

Acetylacetonatorhodiumolefin systems, allylrhodium complexes, or (Ph₃P)₃RhCl catalyzed the conversion of alkenes and molecular oxygen to carbonyl compounds via C?C-bond cleavage. For example, 2,3-dimethyl-2-butene was transformed into acetone. Butadiene and isoprene also undergo oxidative C?C-bond cleavage to form acrylaldehyde and related compounds.     

Oxidative C(Sp)–H activation and C–N cleavage of N-methyl amines under transition-metal-free condition for synthesis of methylene-bridged bis-1,3-diketones

A transition-metal-free oxidative methylenation reaction was developed. Methylene-bridged bis-1,3-dicarbonyl compounds were synthesized by oxidative C(Sp³)–H activation and C–N cleavage of N-methyl amines. This novel reaction avoids the use of transition metal catalyst. Furthermore, the reaction are very mild and operational convenient.     

Photochemically initiated oxidative carbon-carbon bond-cleavage reactivity in chlorodiketonate Ni(II) complexes

Three mononuclear Ni(II) complexes containing a 2-chloro-1,3-diketonate ligand and supported by the 6-Ph(2)TPA chelate, as well as analogues that lack the 2-chloro substituent on the β-diketonate ligand, have been prepared and characterized. Upon irradiation at 350 nm under aerobic conditions, complexes containing the 2-chloro-substituted ligands undergo reactions to generate products resulting from oxidative cleavage, α-cleavage, and radical-derived reactions involving the 2-chloro-1,3-diketonate ligand. Mechanistic studies suggest that the oxidative cleavage reactivity, which leads to the production of carboxylic acids, is a result of the formation of superoxide, which occurs through reaction of reduced nickel complexes with O(2). The presence of the 2-chloro substituent was found to be a prerequisite for oxidative carbon-carbon bond-cleavage reactivity, as complexes lacking this functional group did not undergo these reactions following prolonged irradiation. The approach toward investigating the oxidative reactivity of metal β-diketonate species outlined herein has yielded results of relevance to the proposed mechanistic pathways of metalloenzyme-catalyzed β-diketonate oxidative cleavage reactions.     

Pyrolysis-gas chromatography-mass spectrometry of tricyclic hydroaromatic compounds from coal hydrogenates

Pyrolysis—gas chromatography—mass spectrometry of perhydrophenanthrene, perhydroanthracene and 9,10-dihydrophenanthrene was carried out between 700 and 1000°C in order to study their conversion into light aromatics. The results show that the total hydrogenation of the rings has a great influence on the yields of monoaromatics, obtained by cleavage of the rings and recombination of the fragments. The partially hydrogenated compounds undergo a dehydrogenation reaction, leading back to the stable polycyclic aromatic.     

Deconstructive Oxygenation of Unstrained Cycloalkanamines

A deconstructive oxygenation of unstrained primary cycloalkanamines has been developed for the first time using an auto‐oxidative aromatization promoted C(sp³)?C(sp³) bond cleavage strategy. This metal‐free method involves the substitution reaction of cycloalkanamines with hydrazonyl chlorides and subsequent auto‐oxidative annulation to in situ generate pre‐aromatics, followed by N‐radical‐promoted ring‐opening and further oxygenation by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) and m‐cholorperoxybenzoic acid (mCPBA). Consequently, a series of 1,2,4‐triazole‐containing acyclic carbonyl compounds were efficiently produced. This protocol features a one‐pot operation, mild reaction conditions, high regioselectivity and ring‐opening efficiency, broad substrate scope, and is compatible with alkaloids, osamines, and peptides, as well as steroids.     

Nanosized molecular propellers by cyclodehydrogenation of polyphenylene dendrimers

In a polymer analogous approach, large dendritic oligophenylenes containing benzene and tetraphenylmethane cores are transformed via oxidative cyclodehydrogenation to novel propeller-shaped molecules with large polycyclic aromatic hydrocarbon units as "blades". Structure analysis is performed by a combination of MALDI-TOF mass spectrometry, UV/vis, fluorescence, and Raman spectroscopy using solid-state sample preparation methods. These methods are also utilized to determine the degree of the cyclodehydrogenation reaction.     

Stereoselective cycloadditions of chiral acyl-nitroso compounds; selective reactions of ring-cleaved cycloadducts leading to a new approach to polyoxamic acid

Diesters obtained from diacids produced by oxidative ring cleavage of cycloadducts derived from acyl-nitroso compounds and cyclic 1,3-dienes undergo highly regioselective hydrolysis on reaction with lithium hydroperoxide, which allows for easy differentiation of the carboxyl groups leading to a new approach to polyoxamic acid.     

Oxydation von 2-Jodo-1.3.2-diheteroarsolanen mit o-Chloranil

Oxidation of 2-Iodo-1.3.2-diheteroarsolanes with o-Chloranil The reaction of 2-iodo-1.3.2-diheteroarsolanes with o-chloranil gives via oxidation under simultaneous oxidative cleavage of As? J to bridged spirocyclic As(V) compounds.     

Naphthalene and Acenaphthene Decomposition by Electron Beam Generated Plasma Application

The application of non-thermal plasma generated by electron beam (EB) was investigated in laboratory scale to study decomposition of polycyclic aromatic hydrocarbons like naphthalene and acenaphthene in flue gas. PAH compounds were treated by EB with the dose up to 8 kGy in dry and humid base gas mixtures. Experimentally established G-values gained 1.66 and 3.72 mol/100 eV for NL and AC at the dose of 1 kGy. NL and AC removal was observed in dry base gas mixtures showing that the reaction with OH radical is not exclusive pathway to initialize PAH decomposition, however in the presence of water remarkably higher decomposition efficiency was observed. As by-products of NL decomposition were identified compounds containing one aromatic ring and oxygen atoms besides CO and CO₂. It led to the conclusion that PAH decomposition process in humid flue gas can be regarded as multi-step oxidative de-aromatization analogical to its atmospheric chemistry.     

Oxidative coupling as a potential route to polymers of group IV acetylenes

Bis tert-butyl-, trimethylsilyl- and trimethylgermyl-diacetylenes were prepared from the corresponding ethynyl Group IV compounds via oxidative coupling. Bis(trimethylstannyl)diacetylene could not be prepared by oxidative coupling, but was prepared via another technique. Coupling of diethynyldimethylsilane did not lead to the expected polymer, as cleavage of the silicon–ethynyl bond occurred. However, coupling of 1,3-bis(dimethylethynyl)disiloxane did lead to polymer containing alternating diacetylene and disiloxane units.