Reactions remarkable

A particular case of a [3C+2S] cycloaddition is that described by Sierra et al. related to the tail-to-tail dimerisation of alkynylcarbenes by reaction of these complexes with C8K (potassium graphite) at low temperature and further acid hydrolysis [69] (Scheme 24). In fact, this process should be considered as a [3C+2C] cycloaddition as two molecules of the carbene complex are involved in the reaction. Remarkable features of this reaction are (i) the formation of radical anion complexes by one-electron transfer from the potassium to the carbene complex, (ii) the tail-to-tail dimerisation to form a biscarbene anion intermediate and finally (iii) the protonation with a strong acid to produce the... 

Very recently Chen and co-workers have applied the previously mentioned Ni-based dimetallic pre-catalyst 14 in the Negishi reaction. Remarkable results were obtained even when unactivated aryl chlorides were chosen as reaction partners providing an alternative to the more expensive Pd-based catalysts. The fact that dinuclear pre-catalyst 14 is more active than its mononuclear analogue 13 indicates a possible cooperative effect between the two metal centres [86] (Scheme 6.23). 

During our efforts in profiling (comparative investigations) of several commercial available metathesis catalysts bearing NHC ligands in different types of metathesis reactions remarkable solvent effects were observed [4], Interestingly, the efficiency of most transformations studied frequently depended more on solvent and temperature effects rather than on the nature of Ru precursor and NHC ligands. 

In the latter reaction, remarkable examples of diastereoselectivity have been reported. Thus, the treatment of 7,7-dibromonorcarane 22 with n-butyllithium leads to exo-7-bromo-ewdo-7-lithiobicyclo[4.1.0]heptane23 exclusively, as shown by carboxylation (Scheme 8). It turns out that a slight excess of dibromonorcarane 22 relative to butyllithium is prerequisite to that high degree of stereoselectivity. The result is explained as follows the exo-bromine atom in 22 is exchanged first in a kinetically controlled reaction so that the ewrfo-bromo-exo-lithio-isomer 24 is formed. In a second step, an equilibration occurs by means of another bromine-lithium exchange, which takes place between 24 and the dibromonorcarane 22 (still present because used in excess). Thus, the thermodynamically... 

Tab. 10.7 summarizes the results of the application of rhodium-catalyzed allylic etherification to a series of ortho-substituted phenols. The etherification tolerates alkyls, including branched alkanes (entries 1 and 2), aryl substituents (entry 3), heteroatoms (entries 4 and 5), and halogens (entry 6). These results prompted the examination of ortho-disubstituted phenols, which were expected to be more challenging substrates for this type of reaction. Remarkably, the ortho-disubstituted phenols furnished the secondary aryl allyl ethers with similar selectivity (entries 7-12). The ability to employ halogen-bearing ortho-disubstituted phenols should facilitate substitutions that would have proven extremely challenging with conventional cross-coupling protocols. 

The relevant point to emphasize is that this model allows one to justify the existence of solid-state electrochemical reactions. Remarkably, the redox conductivity is maintained even in the limiting cases where electron diffusion or cation diffusion are hindered. Here, the electrochemical reaction may progress via surface diffusion along the external layer of the particle in contact, respectively, with the electrode and the electrolyte. 

In line with the tremendous renewed activity witnessed in recent years in the field of multicomponent reactions, remarkable new strategies have been developed based on metal-catalyzed coupling processes. Advances in this area take advantage of the myriad of bond-forming processes that can be achieved with metal catalysts. 

Toda, F. Solid State Organic Chemistry Efficient Reactions, Remarkable Yields, and Stereoselectivity, Acc. Chem. Res. 1995, 28, 480-486. 

Measurements of dielectric properties have been used to monitor chemical reactions in organic materials for more than fifty years. In 1934, Kienle and Race 11 reported the use of dielectric measurements to study polyesterification reactions. Remarkably, many of the major issues that are the subject of this review were identified in that early paper the fact that ionic conductivity often dominates the observed dielectric properties the equivalence between the conductivity measured with both DC and AC methods the correlation between viscosity and conductivity early in cure the fact that conductivity does not show an abrupt change at gelation the possible contribution of orientable dipoles and sample heterogeneities to measured dielectric properties and the importance of electrode polarization at low frequencies. 

Benzophenones have been described as useful sensitisers for PET catalysed conjugate addition reactions of a-amino alkyl radicals to enones (Bertrand et al. 2000). We tried to modify this reaction and synthesised the pyrrolidinylethyl-substituted quinolone 35 from the known bromide (Bauer et al. 2005). Upon electron transfer from the pyrrolidine to a given acceptor, a radical cyclisation occurs (Scheme 15), which after electron and proton transfer generates a pyrrolizidine. We found 4,4/-dimethoxybenzophenone to be a suitable catalyst for this reaction. Remarkably, the reaction proceeded with excellent simple diastereos-electivity and a single diastereoisomeric product rac-36 was obtained. With 10 mol% of the catalyst, a chemical yield of 71% was achieved. 

On the other hand, Matsuda et al. [47] recently conducted systematic studies on catalysts for etherification reaction of wood with phenylglycidyl ether (PGE) [47]. It was found that, among various basic catalysts, the K salts of fatty acids accelerate the reaction remarkably, and a high WG indicating a high degree of polyetherification could be obtained. As shown in Table 1,... 

A solid-phase Ugi-Reissert reaction on chloroformate resin, has been reported. The product, the ot-carbamoylated isoquinoline 230, is released by oxidative cleavage (Scheme 33a). Interestingly, the enamide moiety in the adduct can be exploited to perform this process in tandem with a Povarov MCR [189, 190]. In this way, by interaction of dihydroisoquinoline 231 with aldehydes, anilines and a suitable Lewis acid catalyst, the polyheterocyclic system 232 was prepared (Scheme 33b). The Zhu group devised an innovative approach for the synthesis of this class of compounds. They employed the heterocyclic amine 233, which was oxidized in situ to the dihydroisoquinoline 234 with IBX, to undergo the classic Ugi reaction. Remarkably, all the components are chemically compatible, allowing the sequence to proceed as a true MCR (Scheme 33c) [191]. 

It is obvious in Figs. 112 and 113 that, once the rapid oxidativcly-hcating reaction of the sawdust of either wood species begins at temperatures above 200 Pt promotes the reaction remarkably that is, the first exothermic peak shifts to the low temperature side and becomes larger besides. 

Summary The use of an ionic liquid in hydrosilylation reactions enables standard hydrosilylation catalysts to be easily recovered and subsequently reused after separation from the product at the end of the reaction. Remarkably, the recovered catalyst/ionic liquid solution does not need to be purified or treated before its reuse. Employing this method, a variety of organomodified polydiraethylsiloxanes were synthesized. 

We ve now seen that the Sn2 reaction is worst when carried out with a hindered substrate, a neutral nucleophile, and a protic solvent. You might therefore expect the reaction of a tertiary substrate (hindered) with water (neutral, protic) to be among the slowest of substitution reactions. Remarkably, however, the opposite is true. The reaction of the tertiary halide (CHn) )CBr with H2O to give the alcohol 2-methyl-2-propanol is more than 1 million times as fast as the corresponding reaction of the methyl halide CHsBr to give methanol. 

Ooi, T., Miura, T., Itagaki, Y., Ichikawa, H., Maruoka, K. Catalytic Meerwein-Ponndorf-Verley (MPV) and Oppenauer (OPP) reactions remarkable acceleration of the hydride transfer by powerful bidentate aluminum aikoxides. Synthesis 2002, 279-291. 

Some Reactions of the Group lA Metals Reaction Remarks... 

Interestingly, the chiral (S)- +)-sec-butyl "handle" did exert a slight but measurable solution phase asymmetric induction. The solid state results are quite different. In both cases the chiral crystal environment led to a dramatic increase in the formation of one substituted dibenzosemibullvalene configuration over the other (80% ee). A similar large effect was found on the regioselectivity of the solid state reaction. Remarkably, the regioselectivities were found to be different for crystals of (+)-sec-butyl-26 as compared to the ( )-26 samples. This is no... 

It was found, however, that monomers could be quantitatively polymerized by 10 and 11 in the presence of stoichiometric amounts of a strong Bnansted acid [50], The effect of the acid in these systems was determined to be twofold, eliminating small concentrations of detrimental hydroxide ions, and accelerating the rate of metathesis with respect to termination reactions. Remarkably, the acids did not react to decompose the ruthenium alkylidene, and a propagating alkylidene species was clearly observed following complete consumption of monomer. Addition of more monomer to the reaction mixture resulted in further quantitative polymerization, enabling the synthesis of block copolymers. 

F. Toda, Solid state organic chemistry efficient reactions, remarkable yields and stereoselectivity, Acc. 

As indicated by Equation (1), intercalation reactions are usually reversible, and they may also be characterized as topochemical processes, since the structural integrity of the host lattice is formally conserved in the course of the forward and reverse reactions. Typically, these reactions occur near room temperature, but this is in sharp contrast with most conventional solid-state synthetic procedures which often require temperatures in excess of 600 °C, the term Chemie Douce has been coined to describe this type of low-temperature reaction. Remarkably, a wide range of host lattices has been found to undergo these low-temperature reactions, including framework (3D), layer (2D), and linear chain (ID) lattices. 

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