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Silanediols As Hydrogen Bond Donor Catalysts

Schafer, Andrew Gerard
http://rave.ohiolink.edu/etdc/view?acc_num=osu1396442513

Abstract Details

2014, Doctor of Philosophy, Ohio State University, Chemistry.
The design of new catalysts for complex molecule synthesis is a critical endeavor for enabling facile access to medicines and materials. One relatively new direction in catalysis is organic catalysis, which includes classes of small organic molecules capable of facilitating useful transformations that are complementary to reactions catalyzed by metals. Organocatalysis can be further divided into catalysts which operate via covalent and non-covalent interactions. One class of organocatalyts which operate via non-covalent interactions are hydrogen bond donor (HBD) catalysts. Conventional HBD catalysts include (thio)urea, guanidinium, and phosphoric acid functionalities. While these catalysts have proven to be remarkably useful in controlling the outcome of many organic processes, there are limitations in the field including a lack of reactivity patterns and reaction scope. Attempting to overcome these issues, chemists have designed new HBD scaffolds with increased activity. Alternatively, innovative functional groups capable of hydrogen bond donation, such as a silanediol, offer platforms for the design of new HBDs capable of catalyzing reactions which are inaccessible with conventional HBDs. A report from the Kondo laboratory in 2006 demonstrated that silanediols are capable of molecular recognition. However questions about the synthesis and stability of silanediols and whether silanediols were capable of catalysis were unanswered. To this end, we initiated a research program to investigate whether silanediols would be capable of affecting organic reactions. Studies commenced by examining the silanediol-catalyzed addition of indoles to nitroalkenes, a process with benefits under the influence of (thio)ureas. To our delight, we observed that achiral silanediols are capable of catalyzing this transformation in high yield. Further investigation revealed that low yields were obtained in solvents capable of accepting hydrogen bonds and the silanediol functionality was necessary for catalysis. We also observed that under our reaction conditions achiral silanediols outperformed conventional (thio)urea catalysts. Pleased with our data demonstrating achiral silanediols were capable of the HBD catalysis, we moved to examine whether these silanediols would be amenable to other reactivity patterns. We probed the ability of achiral silanediols to activate N-acylisoquinolines for nucleophilic attack, a process that likely proceeds via an anion-binding pathway. Gratifyingly, we observed that achiral silanediols were adept at catalyzing this process in high yield. These data confirmed our hypothesis that silanediols are capable of catalysis. Our efforts then focused on developing chiral silanediols to control the stereochemical outcome of organic processes. We focused on the binaphthyl backbone, as this scaffold has many demonstrated uses as a chiral template. Prior to our work, binaphthyl-derived silanediols were unknown. We prepared a chiral racemic binaphthyl-derived silanediol, confirmed its structure in the solid state, and found that it was capable of catalyzing the addition of indoles to nitroalkenes. We also developed an enantiopure BINOL-derived silanediol and demonstrated that it was capable of the catalyzing the asymmetric addition of silyl ketene acetals to N-acylisoquinolines. This work represents the first synthesis of an enantiopure BINOL-derived silanediol and the first examples of asymmetric silanediol catalysis. Future efforts will consider the synthesis of functionalized BINOL-derived silanediols to increase the stereocontrol exhibited over chemical transformations.
Anita Mattson, PhD (Advisor)
286 p.
Chemistry
organocatalysis; silanediol; anion-binding; hydrogen bond donor

Recommended Citations

Citations

  • Schafer, A. G. (2014). Silanediols As Hydrogen Bond Donor Catalysts [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1396442513

    APA Style (7th edition)

  • Schafer, Andrew. Silanediols As Hydrogen Bond Donor Catalysts. 2014. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1396442513.

    MLA Style (8th edition)

  • Schafer, Andrew. "Silanediols As Hydrogen Bond Donor Catalysts." Doctoral dissertation, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1396442513

    Chicago Manual of Style (17th edition)

osu1396442513
185
© 2014, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.