Browsing by Subject "Monohydrolysis"
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Item Selective monohydrolysis of symmetric diesters and total synthesis of a series of pyrenyl maleimide fluorescent chemosensors(2011-08) Zhao, Tian; Niwayama, Satomi; Birney, David M.As an important desymmetriztion reaction, monohydrolysis facilitates modern synthetic organic chemistry by significantly shortening synthetic routes. Half esters produced by monohydrolysis play an important role in organic synthesis. In chapter 2, we studied the monohydrolysis of symmetric dialkyl benzendicarboxylates, including ortho-phthalate, meta-phthalate, para-phthalate. In addition to the stereochemical effect, the solubility was found to be a possible factor that would affect the selectivity of monohydrolysis. The ultrasound-assisted monohydrolysis of bulky symmetric diesters was also discussed in this chapter. Several bulky diesters were monohydrolyzed with ultrasound. We found out that it was possible to increase the reaction rate by ultrasound without decreasing selectivity. In chapter 3, a mechanism of monohydrolysis was proposed, and the possibility to prove the mechanism by measuring critical micelle concentrations of intermediates is discussed. In additional to the research on monohydrolysis, a synthetic study of a series of new and effective pyrenyl maleimide fluorescent probes for sampling of longer inter-thiol distances was also conducted. In chapter 4, the syntheses of pyrenylbutyl maleimide, pyrenyloctyl maleimide and pyrenyldecyl maleimide were discussed. Further spectroscopic characterization of pyrenylbutyl maleimide showed it was an excellent probe to assess proximities between cysteine in proteins or thiols in macromolecules, and to follow conformational changes.Item SELECTIVE MONOHYDROLYSIS OF SYMMETRIC DIESTERS IN MAINLY AQUEOUS MEDIA(2010-12) Cho, Hanjoung; Niwayama, Satomi; Li, Guigen; Mayer, Michael F.As water possesses many ideal characteristics for a reaction medium such as accessibility, environmental safety, and low cost, the development of organic reactions in aqueous media has been of central importance in recent organic chemistry. Since many organic compounds have limited solubility in water, efficient water-mediated reactions with high selectivities and reactivities are still somewhat rare, and hence there is a need for organic methodological development in mainly water media. The desymmetrization of meso compounds is a powerful concept with regards to both asymmetric and nonasymmetric synthesis. Half-esters produced by desymmetrization of symmetric diesters are especially versatile building blocks in organic synthesis. In this dissertation, the syntheses of various half-esters from the corresponding diesters via monohydrolysis, which is a desymmetrization reaction, in mainly water media are discussed. The highly selective monohydrolysis of dialkyl malonates and their derivatives are discussed. In the second chapter, the reactions are practical, yielding the corresponding half-esters in high yields in a straightforward manner without inducing decarboxylation. The hydrophobicity of diester substrates was found to be one of the factors which could determine the selectivity in monohydrolysis reactions. The high exo-facial selectivity observed in the selective monohydrolysis of a series of near-symmetric diesters is described in the third chapter. The selectivities were found to be specific, although the reaction center in these reactions is one covalent bond distant from the norbornane or norbornene ring, where the difference of the environment between the exo face and endo face is expected to be negligible. In addition to these experimental studies, the conformational studies in symmetric diesters showed electronic interaction between the two carbonyl groups via computational calculations in the fourth chapter. The stable structures of symmetric diesters with attractive interaction on the two carbonyl groups are presented. This conformational preference is expected to contribute to the high selectivities in the monohydrolysis of symmetric diesters. The asymmetric monohydrolysis of symmetric diester is also investigated with chiral ionic liquids in the last chapter. Since the reactivity of selective monohydrolysis of symmetric diesters with an alkali base could be affected on the choice of co-solvents, the chiral ionic liquids can influence the chirality of half-ester by selective monohydrolysis. The studies to improve the enantiomeric excesses of half-esters by the modification of substrates and chiral ionic liquids are underway.