Breslow studies

Breslow studied the dimerisation of cyclopentadiene and the reaction between substituted maleimides and 9-(hydroxymethyl)anthracene in alcohol-water mixtures. He successfully correlated the rate constant with the solubility of the starting materials for each Diels-Alder reaction. From these relations he estimated the change in solvent accessible surface between initial state and activated complex " . Again, Breslow completely neglects hydrogen bonding interactions, but since he only studied alcohol-water mixtures, the enforced hydrophobic interactions will dominate the behaviour. Recently, also Diels-Alder reactions in dilute salt solutions in aqueous ethanol have been studied and minor rate increases have been observed Lubineau has demonstrated that addition of sugars can induce an extra acceleration of the aqueous Diels-Alder reaction . Also the effect of surfactants on Diels-Alder reactions has been studied. This topic will be extensively reviewed in Chapter 4. 

Benzoin Condensation. The benzoin condensation is a related reaction consisting of treating an aromatic aldehyde with potassium cyanide or sodium cyanide usually in an aqueous ethanolic solution. Breslow studied the effects of inorganic salts on the rate... 

The effect of water on Diels-Alder reactions has been studied extensively by various theoretical and experimental methods. It was mentioned previously that Breslow studied the influence of the hydrophobic effect on the aqueous Diels-Alder reactions in detail8,9 while the volumes of activation for catalyzed Diels-Alder reactions were examined by Isaacs et al.69... 

R. Breslow, Studies in Biomimetic Chemistry , Pure Appl. Chem., 70, 267 (1998)... 

Shono and coworkers studied the electrochemical formation of triphenylcyclopropenyl radical and its chemical behavior in the presence of hydrogen donors and olefins (Table 10). Wasielevsky and Breslow studied the reduction of various cyclopropenyl cations by second harmonic AC voltammetry (Table 11). They detected adsorption effects for some of the cations at the Pt but not at the Au electrode. The electrochemical data were used in thermodynamic sequences to evaluate the basicity of various cycloproenyl anions as well as the C-O bond dissociation energy of cyclopropenols. 

In this pioneering work [la], Breslow studied the kinetics of the cycloaddition between cyclopentadiene and methyl vinyl ketone (Eq. (1) and Table 1). The implication of the hydrophobic effect in Diels-Alder reactions was extensively supported by the effect of cyclodextrins [26] and additives, such as lithium chloride (salting-out agent) or guanidinium chloride (salting-in agent), which respectively increases or decreases the rate of the reaction [27]. 

The extreme influence water can exert on the Diels-Alder reaction was rediscovered by Breslow in 1980, much by coincidence . Whale studying the effect of p-cyclodextrin on the rate of a Diels-Alder reaction in water, accidentally, the addition of the cyclodextrin was omitted, but still rate constants were observed that were one to two orders of magnitude larger than those obtained in organic solvents. The investigations that followed this remarkable observation showed that the acceleration of Diels-Alder reactions by water is a general phenomenon. Table 1.2 contains a selection from the multitude of Diels-Alder reactions in aqueous media that have been studied Note that the rate enhancements induced by water can amount up to a factor 12,800 compared to organic solvents (entry 1 in Table 1.2). 

A few years after the first articles of Breslow had appeared, Grieco elegantly demonstrated that the astonishing rate and selectivity enhancements of Diels-Alder reactions in water can be exploited sirccessfully in organic synthesis. He extensively studied the reactivity of dienes containing... 

Professor Ronald Breslow of Columbia University has car ried out a number of organic reactions in the presence of cyclodextrms to study the effect of a molecule s envi ronment on its chemical reactivity... 

Alkylations of phenoxide ions in water have recently been carefully studied by Breslow et al.57 Alkylation can occur both at the phenoxide oxygen and on ortho and para positions of the ring when the phenoxide has at least one alkyl substituent (Eq. 5.4). Carbon alkylation occurs in water, but not in nonpolar organic solvents. This is attributed to the antihydrophobic effect of the organic solvents. 

As part of their study of enzyme models capable of remote oxidation, Breslow and co-workers have used a benzophenone derivative to function-... 

To determine whether a more rigid conformation would increase the degree of selectivity of this remote oxidation, Breslow and Baldwin studied a similar system using the 3-a-cholestanol moiety,(77)... 

It is known that the reduction potentials of quinones are related to the aromatic stabilization of the parent conjugated systems. In an attempt to relate the annulenediones 171,177, and 178 to the tetradehydro[18]annuIene system Breslow and coworkers63 have studied their electrochemical reduction by cyclic voltammetry. These diones can easily be reduced to the corresponding dianions, e.g. 171 - 179. These... 

The photochemistry of [26] was first studied by Breslow and Winnik (1969). The excited triplet state undergoes intramolecular hydrogen abstraction which quenches the excited state and shortens the triplet lifetime. Here cyclisation involves the chain interior, each CH2 group being inherently... 

Shahrokh Saba was born in Tehran, Iran, studied at the American University of Beirut, Lebanon, where he obtained his B.S. in 1970. He continued his education at the University of East Anglia and received his Ph.D. in 1974 under the direction of Prof. A. R. Katritzky. During 1975-79, he taught as an assistant professor at Azad University in Tehran. He moved to the United States in 1980, and after postdoctoral fellowships in 1980 (Prof. R. Breslow, Columbia University), 1981 (Prof. W. C. Agosta, Rockefeller University), and 1982-83 (Prof. N. O. Smith, Fordham University), he assumed a teaching position at Kean College of New Jersey in 1984. He returned to Fordham University in 1986 and took up his present position, and is currently an associate professor of chemistry. His scientific interests include all aspects of heterocyclic chemistry, and new uses of simple ammonium salts in organic synthesis. 

The pioneering studies of Bender s group were followed by many attempts to increase the efficiency of esterolysis by cyclodextrins and several approaches have been tried, most notably in Breslow s laboratory. One may optimize the structure of the substrate (Trainor and Breslow, 1981 Breslow et al., 1983), modify the cyclodextrin (Emert and Breslow, 1975 Breslow et al., 1980 Fujita et al., 1980), or alter the solvent (Siegel and Breslow, 1975). The last of these is the easiest to achieve but detailed studies are made tedious by the necessity to redetermine all of the relevant equilibrium and rate constants, and the acidity dependence of the catalysed and uncatalysed processes, in the new medium. 

The first kinetic study of acceleration of some Diels-Alder reactions in water by Breslow et al. has set the stage for worldwide interest in organic... 

Czamieki and Breslow (22) have studied the rate of acyl transfer from a substrate that is bound by the acyl part rather than by the leaving group. Having shown that ferrocene binds strongly to -cyclodextrin, Czamiecki and Breslow employed the p-nitrophenyl ester of ferrocinnamic acid in kinetic studies using DMSO-buffer mixtures. A rate acceleration of 51,000 times background was observed for acylation of /i-cyclodextrin. 

Since mechanistic studies modeling the Stetter reaction have not yet been reported, the proposed mechanism is based on that elucidated by Breslow for the thiazolium catalyzed benzoin reaction (Scheme 9). The carbene, formed in situ by deprotonation... 

Following TSA, probably the most widely studied H DACi is vorinostat (2 SAHA/ Zolinza). Interestingly, the discovery of this compound arose by chance, as the groups of P. Marks, R. Breslow and R. Rifkind were working to understand the mechanism... 

Breslow suggested a mechanistic scheme (Scheme 8.1) involving a zwitterionic metal alkyl species, with a tetrahedral geometry of the titanium center. However, it was not possible at the time to provide direct structural evidence for these species. Alternative suggestions, e.g. by Olive et al. [11], included octahedral intermediates (Scheme 8.2), while an early proposal by Shilov et al. [12], based on electrochemical studies in dichloromethane, that the active species was likely to be... 

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