1844-00-4Relevant academic research and scientific papers
Linear free-energy relationship analysis of a catalytic desymmetrization reaction of a diarylmethane-bis(phenol)
Gustafson, Jeffrey L.,Sigman, Matthew S.,Miller, Scott J.
supporting information; experimental part, p. 2794 - 2797 (2010/09/04)
(Figure presented) Linear free-energy relationships have been found for enantioselectivity and various steric parameters in an enantioselective desymmetrization of symmetrical bis(phenol) substrates. The potential origin of this observation and the role of different steric parameters are discussed.
A case of remote asymmetric induction in the peptide-catalyzed desymmetrization of a bis(phenol)
Lewis, Chad A.,Gustafson, Jeffrey L.,Chiu, Anna,Balsells, Jaume,Pollard, David,Murry, Jerry,Reamer, Robert A.,Hansen, Karl B.,Miller, Scott J.
supporting information; experimental part, p. 16358 - 16365 (2009/05/09)
We report a catalytic approach to the synthesis of a key intermediate on the synthetic route to a pharmaceutical drug candidate in single enantiomer form. In particular, we illustrate the discovery process employed to arrive at a powerful, peptide-based asymmetric acylation catalyst. The substrate this catalyst modifies represents a remarkable case of desymmetrization, wherein the enantiotopic groups are separated by nearly a full nanometer, and the distance between the reactive site and the pro-stereogenic element is nearly 6 A. Differentiation of enantiotopic sites within molecules that are removed from the prochiral centers by long distances presents special challenges to the field of asymmetric catalysis. As the distance between enantiotopic sites increases within a substrate, so too may the requirements for size and complexity of the catalyst. The approach presented herein contrasts enzymatic catalysts and small-molecule catalysts for this challenge. Ultimately, we report here a synthetic, miniaturized enzyme mimic that catalyzes a desymmetrization reaction over a substantial distance. In addition, studies relevant to mechanism are presented, including (a) the delineation of structure-selectivity relationships through the use of substrate analogs, (b) NMR experiments documenting catalyst-substrate interactions, and (c) the use of isotopically labeled substrates to illustrate unequivocally an asymmetric catalyst-substrate binding event.
Metal cation-exchanged montmorillonite (Mn+-mont)-catalysed aromatic alkylation with aldehydes and ketones
Tateiwa, Jun-Ichi,Hayama, Ei,Nishimura, Takahiro,Uemura, Sakae
, p. 1923 - 1928 (2007/10/03)
The alkylation of aromatic compounds with aldehydes and ketones in the presence of a variety of metal cation-exchanged montmorillonites (Mn+-mont; Mn+ = Zr4+, Al3+, Fe3+, Zn2+, H+, Na+) has been investigated. Al3+- and Zr4+-Monts are revealed to be effective as catalysts, while no reaction takes place with Na+-mont. Al3+-Mont-catalysed alkylation of phenol with several aldehydes produces mainly or almost solely the corresponding gem-bis(hydroxyphenyl)alkanes (bisphenols) in good yields, while that with several ketones affords selectively the corresponding alkylphenols in moderate to good yields. The alkylation always occurs at the carbonyl carbon without any skeletal rearrangement and the kind of products depends much on the steric hindrance of an electrophilic intermediary carbocation. The alkylation of anisole, veratrole and p-cresol proceeds well, while that of toluene, benzene, chlorobenzene and nitrobenzene scarcely occurs.
Processes for producing aromatic polycarbonate oligomer and aromatic polycarbonate
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, (2008/06/13)
A process for producing continuously an aromatic polycarbonate oligomer by reacting an aromatic dihydroxy compound and an alkali metal base or an alkaline earth metal base with a carbonyl halide compound comprises: (1) feeding continuously to a tank reactor an aromatic dihydroxy compound, water, a molecular weight controlling agent, a polymerization catalyst, a carbonyl halide compound, and an organic solvent, and an alkali metal base or an alkaline earth metal base in an amount of 1.15-1.6 equivalents based on the aromatic dihydroxy compound, (2) carrying out the reaction with a residence time as defined by the following formula, where X is an amount of the polymerization catalyst in terms of mole % based on the amount of mole of the aromatic dihydroxy compound fed per unit time, and Y is a residence time (min.), and (3) continuously withdrawing the reaction mixture from the tank reactor to obtain an aromatic polycarbonate oligomer having a number average molecular weight of 1,000-10,000. An aromatic polycarbonate is produced by polycondensation of the aromatic polycarbonate oligomer.
Method for preparing aromatic bischloroformate compositions
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, (2008/06/13)
Bischloroformate oligomer compositions are prepared by passing phosgene into a heterogeneous aqueous-organic mixture containing at least one dihydroxyaromatic compound, with simultaneous introduction of a base at a rate to maintain a specific pH range and to produce a specific volume ratio of aqueous to organic phase. By this method, it is possible to employ a minimum amount of phosgene. The reaction may be conducted batchwise or continuously. The bischloroformate composition may be employed for the preparation of cyclic polycarbonate oligomers or linear polycarbonate, and linear polycarbonate formation may be integrated with bischloroformate composition formation in a batch or continuous process.
Bischoloroformate preparation method with phosgene removal and monochloroformate conversion
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, (2008/06/13)
Aqueous bischloroformates are prepared by the reaction of a dihydroxyaromatic compound (e.g., bisphenol A) with phosgene in a substantially inert organic liquid (e.g., methylene chloride) and in the presence of an aqueous alkali metal or alkaline earth metal base, at a pH below about 8. After all solid dihydroxyaromatic compound has been consumed, the pH is raised to a higher value in the range of about 7-12, preferably 9-11, and maintained in said range until a major proportion of the unreacted phosgene has been hydrolyzed. At the same time, any monochloroformate in the product may be converted to bischloroformate.
Cyclic monocarbonate bishaloformates
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, (2008/06/13)
Cyclic monocarbonate bischloroformates are prepared by the reaction of a carbonyl halide such as phosgene with a bridged substituted resorcinol or hydroquinone such as bis(2,4-dihydroxy-3-methylphenyl)methane or bis(2,5-dihydroxy-3,4,6-trimethylphenyl)methane in the presence of aqueous alkali metal hydroxide. The cyclic monocarbonate bischloroformates may be used for the preparation of linear or cyclic polycarbonates containing cyclic carbonate structural units, which may in turn be converted to crosslinked polycarbonates.
SYNTHESIS OF BENZYL ESTERS OF 2,2-DIMETHYL-3-(4-DIFLUOROMETHOXYPHENYL)CYCLOPROPANE CARBOXYLIC ACID - CYCLIC ANALOGS OF PYRETHROID FLUOROCITRINATE
Shapiro, E. A.,Eismont, M. Yu.,Pereverzeva, Yu. O.,Nefedov, A. O.,Srashnenko, A. V.,et al.
, p. 573 - 577 (2007/10/02)
3-Phenoxybenzyl and α-cyano-3-phenoxybenzyl esters of 2,2-dimethyl-3-(4-difluoromethoxyphenyl)cyclopropane carboxylic acid have been synthesized.The latter compound, which is the cyclopropane analog of pyrethroid fluorocitrinate, has moderate insecticide activity toward the housefly.
Polyetherimide bisphenol compositions
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, (2008/06/13)
Polyetherimide bisphenols and bischloroformates are prepared by the reaction of dianhydrides or certain bisimides with aminophenols or mixtures thereof with diamines. They are useful as intermediates for the preparation of cyclic heterocarbonates, which may in turn be converted to linear copolycarbonates. The bisphenols can also be converted to salts which react with cyclic polycarbonate oligomers to form block copolyetherimidecarbonates.
