Thesis advisor: Marc L. Snapper / Chapter 1: Brief overview of the catalytic enantioselective functionalization and kinetic resolution of alcohols Chapter 2: Kinetic resolution of syn-diols by catalytic enantioselective sulfonylation Chapter 3: Significant improvement on catalytic enantioselective silylation of syn-diols and triols through the use of a tetrazole additive / Thesis (MS) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis details the design and development of pentacarboxycyclopentadienes (PCCPs) as a new platform for enantioselective Brønsted acid catalysis. Prior to this research, enantioselective Brønsted acid catalysis was limited to the BINOL (and variations thereof) framework. While this catalyst platform has paved the way for a myriad of novel asymmetric chemical transformations, the utility of this catalyst scaffold has suffered from its lengthy and expensive preparations. As an alternative, starting from readily available 1,2,3,4,5-pentacarbomethoxycyclopentadiene and various chiral alcohols and amines, the synthesis of a library of strongly acidic chiral catalysts is described. The utility of these novel acid catalysts is explored in various transformations. As a prelude to the heart of this work, Chapter 1 focuses on the advancements made in asymmetric Brønsted acid catalysis through BINOL-phosphate derived catalysts, focusing on the major accomplishments made by researchers since 2004. The provided review highlights the utility of these chiral acid catalysts but also reveals the need for a new scaffold that is more affordable and accessible. Chapter 2 discusses the background of PCCPs, including its initial discovery and subsequent applications. Our work in developing novel transesterified and amidated derivatives is discussed with accompanying crystal structures of achiral and chiral PCCPs. pKa measurements demonstrate the capacity of PCCPs to be used as strong Brønsted acid catalysts and are compared to literature values of known Brønsted acid catalysts. Chapter 3 focuses on the utility of PCCPs as enantioselective Brønsted acid catalysts in a variety of chemical transformations including the Mukaiyama-Mannich reaction, transfer hydrogenation, Pictet-Spengler reaction, diaryl alcohol substitution, Mukayaiama oxocarbenium aldol reaction, and [4+2]-cycloaddition. Catalyst loadings down to 0.01 mol% and reaction scale up to 25 grams in the Mukaiyama-Mannich reaction demonstrate the practical utility and robustness of PCCPs. Substrate scopes of these transformations show the breadth of accessible molecules that can be synthesized via PCCPs. Mechanistic rationales and transition state analyses are discussed in each of the transformations.

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Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed May 22, 2007). PDF text: 466 p. : ill. ; 17.94Mb. UMI publication number: AAT3237597 . Includes bibliographical references. Also available in microfilm and microfiche formats.

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(+)-(2R,3R)-1,1,4,4-Tetraphenylbutane-1,2,3,4-tetraol (TETROL) and its derivatives were reacted with varying molar ratios of titanium isopropoxide (2:1, 1:1 and 1:2 tetraol:titanium isopropoxide) in an attempt to prepare potential titanium-based tetraol catalysts for enantioselective transformations. In each case, infrared and HNMR spectra suggested that the product was formed. We tentatively proposed that the structure of the catalyst was a spiro-type, but we could not determine conclusively what its exact structure was, despite using numerous techniques at our disposal (molecular modelling calculations, H NMR and IR spectroscopy, thermal analyses, powder diffraction, and single crystal X-ray diffraction). The catalyst and derivatives thereof were able to act catalytically for the enantioselective additions of diethylzinc compounds to aldehydes. The effects of temperature and solvent were investigated, and toluene and -78 °C were selected as optimal from the results obtained. (The reaction could, however, not be maintained at this low temperature for extended periods due to the fact that we did not have, at our disposal, the correct equipment. Each 16 h reaction was thus allowed to reach room temperature in each case.) The selectivity for the product 1-phenylpropan-1-ol (when benzaldehyde was the starting aldehyde) varied depending on the nature of the aryl substituents of the titanium-based catalyst. Using 0.2 molar equivalents of the chiral titanates, the highest selectivity was 42 percent (e.e.), but only when excess Ti(O-i-Pr)4 had been added to the reaction mixture. This was achieved with the tetra(ortho-methoxyphenyl)-TETROLate derivative. TETROL and its derivatives were also successful in metal-free catalysis where higher conversions and selectivities were observed, compared to when these were complexed to titanium. The highest selectivity was 70 percent (e.e.), achieved with the tetra(ortho-methylphenyl)TETROL derivative.

Thesis advisor: Amir H. Hoveyda / Homoallylic amines and alcohols, particularly those amenable to further functionalization, are among the most widely used building blocks in chemical synthesis and are typically accessed by addition of an allyl-metal compound to an electrophile. Studies discussed herein have focused on advancing stereoselective synthesis of versatile allylboron compounds and their utilization in catalytic regio-, diastereo-, and enantioselective addition to various electrophiles. Mechanistic principles have been central to the investigations described in this thesis, and it has been on this basis that catalytic strategies for practical synthesis of bioactive molecules were developed. Chapter One. Vicinal amino alcohols are ubiquitous in natural products and serve as versatile synthetic intermediates and we envisaged that diastereo- and enantioselective additions of O-substituted allyl boronates offers an attractive option to access these motifs. In the presence of zinc (II) methoxide as co-catalyst, it will be demonstrated that sequence of events may occur, wherein isomerization of an initially formed allyl complex occurs prior to addition of an aldimine with kinetic selectivity. As will be described, through the use of an optimal catalyst, N-protecting/activating group and appropriate reaction conditions, differentially protected vicinal amino alcohol derivatives may be synthesized in high enantiopurity. The utility of the approach is highlighted through synthesis of an NK1 agonist. Chapter Two. It will be demonstrated that additions of various organoboron compounds converts readily accessible and easy-to-handle silyl-substituted -tertiary amines. Contrary to additions to aldimines, isomerization of the initially generated aminophenol-allyl complex is preempted, suchthat linear products are favored. DFT analysis suggests that high enantioselectivity likely originates from attractive electrostatic interaction between a trifluoromethyl group and the catalyst’s ammonium moiety. The synthetic utility was highlighted through concise, enantioselective synthesis of a key intermediate of a recently reported BACE-1 inhibitor on gram scale. Chapter Three. This section details the development of a method for direct synthesis of homoallylic alcohols bearing a Z-alkenyl chloride, which may be directly subjected to stereo-retentive cross coupling without wasteful protection/deprotection or redox operations. Products were obtained in high regio- and enantioselectivity for aliphatic, alkenyl- and heteroaryl-substituted aldehydes. The approach was utilized in a concise, protecting group-free synthesis of anti-tumor agent mycothiazole. Chapter Four. A method for stereoselective synthesis of fluorine-containing trisubstituted allyl boronates will be presented. It will then be illustrated that in the presence of an appropriate aminophenol catalyst, a large assortment of homoallylic alcohols containing a quaternary fluoro- and trifluoromethyl-substituted stereogenic center may be obtained with efficiency and high diastereo- and enantioselectivity. The obtained products were then elaborated to the furanose core of Sofosbuvir, a recently approved treatment for hepatitis C. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Amir H. Hoveyda / Homoallylic alcohols and amines are commonly used building blocks for synthesis of biologically active molecules, yet a survey of the methods for their synthesis reveals a plague of limitations. Notably, the use of toxic reagents (Cr-, Mn-, and Sn-containing), precious metal catalysts (Ir- and In-based), non-ambient reaction temperatures (–78 to 140 °C), and extended reaction times (up to 240 hours), limit application on larger scale. The protection/deprotection sequences required to install directing/activating groups for reaction efficiency and enantioselectivity not only add synthetic steps but the conditions required for removal of such entities are not amenable to more complex and sensitive molecules. The development of catalytic enantioselective methods for addition of allyl moieties to readily available substrates including halomethyl ketones, trifluoromethyl-substituted ketimines, and nitriles have been developed. In the first two cases, an aminophenol-based boryl catalyst is utilized for enantioselective additions of allyl moieties through transition states controlled by either electrostatic attraction between a C–X bond and the catalyst’s ammonium moiety or minimization of steric and dipolar repulsion. In the latter, multicomponent additions to nitriles have been developed for synthesis of cyclic amines. In all cases, application is demonstrated through synthesis of otherwise difficult-to-access derivatives or biologically active molecules. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Amir H. Hoveyda / A previously developed catalytic system which can catalyze a variety of efficient and enantioselective allyl additions has been expanded to include regio-, diastereo-, Z-, and enantioselective crotyl addition reactions. As discussed in Chapter 1, we were able to carry out efficient crotyl additions to N-phosphinoyl imines by discovering a sufficiently Lewis acidic co-catalyst, zinc(II) methoxide. This finding enabled us to vastly improve reaction efficiency, in addition to enabling a 1,3-borotropic shift during the course of the reaction, turning a previously α selective transformation into a γ-selective one. These findings allowed us to develop a catalytic, enantioselective crotyl addition to N-phosphinoyl imines utilizing the commercially available Z-crotyl–B(pin). When the reaction conditions elucidated for crotyl additions to imines were utilized on a more electrophilic substrate, such as trifluoromethyl ketones, an entirely different finding was observed (Chapter 2). We found that if direct addition is more facile than 1,3-borotropic shift the transformation will again be α-selective, furnishing a linear product, rather than the typically observed, branched crotyl addition product. This finding allowed us to establish the first broadly applicable, efficient, regio-, Z-, and enantioselective crotyl addition to trifluoromethyl ketones. We then highlighted the utility of these products by using this method in tandem with Z-selective olefin metathesis, affording complex, enantioenriched, trifluoromethyl-containing homoallylic alcohols. During the course of these studies, and through density functional theory computations, we learned that Z- and E-crotyl–B(pin) react through distinct transition states to form the same Z-olefin-containing product with varying levels of enantioselectivity. These findings led us to the results reported in Chapter 3, the first examples of enantioselective aminophenol-promoted allyl additions to aldehydes. We were able to utilize Z-CF3-allyl–B(pin) and Z-Cl-allyl–B(pin) (both accessed through catalytic olefin metathesis) in Z- and enantioselective additions to aldehydes, affording products which cannot be accessed readily through previously reported methods. We quickly realized the potential of Z-chloro-substituted homoallylic alcohols for the synthesis of Z-homoallylic alcohols, to demonstrate this potential, we carried out the total synthesis of mycothiazole, which we accomplished in seven steps from commercially available materials and 17% overall yield, a marked improvement over the previous synthetic strategy. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.