Strong and Confined Acids Enable a Catalytic Asymmetric Nazarov Cyclization of Simple Divinyl Ketones

We report a catalytic asymmetric Nazarov cyclization of simple, acylic, alkyl-substituted divinyl ketones using our recently disclosed strong and confined imidodiphosphorimidate Brønsted acids. The corresponding monocyclic cyclopentenones are formed in good yields and excellent regio-, diastereo-, and enantioselectivities. Further, the chemical utility of the obtained enantiopure cyclopentenones is demonstrated

Catalytic Asymmetric Hydroalkoxylation of C–C Multiple Bonds

Asymmetric hydroalkoxylation of alkenes constitutes a redox-neutral and 100% atom-economical strategy toward enantioenriched oxygenated building blocks from readily available starting materials. Despite their great potential, catalytic enantioselective additions of alcohols across a C–C multiple bond are particularly underdeveloped, especially compared to other hydrofunctionalization methods such as hydroamination. However, driven by some recent innovations, e.g., asymmetric MHAT methods, asymmetric photocatalytic methods, and the development of extremely strong chiral Brønsted acids, there has been a gratifying surge of reports in this burgeoning field. The goal of this review is to survey the growing landscape of asymmetric hydroalkoxylation by highlighting exciting new advances, deconstructing mechanistic underpinnings, and drawing insight from related asymmetric hydroacyloxylation and hydration. A deep appreciation of the underlying principles informs an understanding of the various selectivity parameters and activation modes in the realm of asymmetric alkene hydrofunctionalization while simultaneously evoking the outstanding challenges to the field moving forward. Overall, we aim to lay a foundation for cross-fertilization among various catalytic fields and spur further innovation in asymmetric hydroalkoxylations of C–C multiple bonds

Microphase separation of highly amphiphilic, low N polymers by photoinduced copper-mediated polymerization, achieving sub-2 nm domains at half-pitch

The lower limit of domain size resolution using microphase separation of short poly(acrylic acid) homopolymers equipped with a short fluorinated tail, posing as an antagonist 'A block' in pseudo AB block copolymers has been investigated. An alkyl halide initiator with a fluorocarbon chain was utilized as a first 'A block' in the synthesis of low molecular weight polymers (1400-4300 g mol -1) using photoinduced Cu(ii)-mediated polymerization allowing for very narrow dispersity. Poly(tert-butyl acrylate) was synthesized and subsequently deprotected to give very low degrees of polymerization (N), amphiphilic polymers with low dispersity (D = 1.06-1.13). By exploiting the high driving force for demixing and the well-defined 'block' sizes, we are able to control the nanostructure in terms of domain size (down to 3.4 nm full-pitch) and morphology. This work demonstrates the simple and highly controlled synthesis of polymers to push the boundaries of the smallest achievable domain sizes obtained from polymer self-assembly

The Development of Strong Chiral Brønsted Acids for Asymmetric Hydrofunctionalizations of Olefins

The main objective of this thesis is to design and synthesize chiral Brønsted acids capable of catalyzing the functionalization of weakly basic olefins. Olefins are a particularly intriguing substrate class because while they are widely available, many being considered feedstock chemicals, they have so far eluded asymmetric organocatalysis. In our efforts to resolve this major limitation of the field, our group recently reported an intramolecular asymmetric hydroalkoxylation using highly confined and chiral Brønsted acids, imidodiphosphorimidates (IDPi), to provide enantioenriched tetrahydrofurans and tetrahydropyrans in high yields and excellent enantioselectivities. Mechanistic investigations, including computational and kinetic analyses, suggest that the reaction proceeds via a concerted, though asynchronous pathway, in which the reaction is initiated by protonation of the olefin followed by C−O bond formation. The PhD studies described herein have focused on accessing similar reactivity in intermolecular systems. Namely, in chapter 2 of this thesis, the development of an intermolecular hydroalkoxylation reaction of styrenyl olefins with oxygenated nucleophiles is described. In particular, we report the hydroalkoxylation of styrene with benzyl alcohol to afford the corresponding ether in 95% yield with a very promising enantioselectivity (er = 76.5:23.5). The reaction is tolerant of a range of nucleophilic partners, including alcohols, carboxylic acids, and phenols to yield the corresponding functionalized products with moderate degrees of enantioinduction. Our efforts to increase the enantioselectivity of these transformations through catalyst optimization are delineated. Further, we report preliminary investigations into the asymmetric hydroalkoxylation of structurally-simple olefins. In chapter 3, we report the development of a new class of highly acidic chiral catalysts, deemed imido-(N,Nʹ-bis(sulfonimidoyl))-diphorphorimidates (I2DPi’s). This development was inspired by the work of Yagupolskii, who, among others, has described dramatic increases in the acidity of neutral molecules toward superacids by substituting S=O bonds with S=NSO2CF3 (S=NTf) bonds. These novel scaffolds not only enable significantly increased reactivity in both Brønsted and Lewis acid catalysis, but uniquely provide two additional chiral handles for tuning enantioselectivity within the catalyst pocket, potentially offering new avenues in acid catalyzed transformations

Variable Temperature ROMP: Leveraging Low Ring Strain Thermodynamics To Achieve Well-Defined Polypentenamers

Living-like conditions through ring-opening metathesis polymerization (ROMP) of low ring strain monomers were achieved through temperature variation during the reaction. For a variety of solvents and readily available ruthenium-based catalysts, warm initiation to low conversions followed by immediate thermal quenching and subsequent propagation to high conversions produced polycyclopentene with molar masses close to theoretical and with moderately low dispersities (<i>Đ</i> ≤ 1.3 ± 0.1). Optimization using Grubbs first-generation catalyst and THF as the solvent consistently resulted in narrow dispersities (<1.2) at various molar masses targeted which increased linearly with monomer-to-catalyst ratio. In all cases, intermolecular chain transfer reactions were suppressed at colder temperatures as evidenced by low dispersity for up to 300 min at 0 °C. This approach was extended to 3-cyclopentenol to emphasize the universality of the methodology to other low ring strain monomers with functional group tolerance specific to Ru-based catalysts

Viscoelastic, Mechanical, and Glasstomeric Properties of Precision Polyolefins Containing a Phenyl Branch at Every Five Carbons

Mechanical and viscoelastic properties of precision polyolefins, poly­(4-phenylcyclopentene) (P4PCP) and its hydrogenated analog (H₂-P4PCP) containing atactic phenyl branches at exactly every five carbons along the backbone are explored. Both materials are amorphous with a glass transition temperature of ∼17 ± 3 °C. Rheological investigations determined that P4PCP has an entanglement molar mass (<i>M</i>_e = 10.0 kg mol^–1) much higher and closer to polystyrene than H₂-P4PCP (<i>M</i>_e = 3.6 kg mol^–1). Both materials have elastomeric and shape memory properties at ambient temperatures, which were further explored through strain hysteresis measurements. H₂-P4PCP has an elastic recovery of ∼95% at max strain values up to 500% as determined by uniaxial tensile testing. Time–temperature superposition analysis, Williams–Landel–Ferry constants, and further mechanical analysis are discussed and compared to previously reported ethylene–styrene copolymers of similar phenyl-branch content within the microstructure

The Silicon−Hydrogen Exchange Reaction: A Catalytic σ‑Bond Metathesis Approach to the Enantioselective Synthesis of Enol Silanes

The use of chiral enol silanes in fundamental transformations such as Mukaiyama aldol, Michael, and Mannich reactions as well as Saegusa–Ito dehydrogenations has enabled the chemical synthesis of enantiopure natural products and valuable pharmaceuticals. However, accessing these intermediates in high enantiopurity has generally required the use of either stoichiometric chiral precursors or stoichiometric chiral reagents. We now describe a catalytic approach in which strongly acidic and confined imidodiphosphorimidates (IDPi) catalyze highly enantioselective interconversions of ketones and enol silanes. These “silicon–hydrogen exchange reactions” enable access to enantiopure enol silanes via tautomerizing σ-bond metatheses, either in a deprotosilylative desymmetrization of ketones with allyl silanes as the silicon source or in a protodesilylative kinetic resolution of racemic enol silanes with a carboxylic acid as the silyl acceptor

Activation of olefins via asymmetric Brønsted acid catalysis

The activation of olefins for asymmetric chemical synthesis traditionally relies on transition metal catalysts. In contrast, biological enzymes with Brønsted acidic sites of appropriate strength can protonate olefins and thereby generate carbocations that ultimately react to form natural products. Although chemists have recently designed chiral Brønsted acid catalysts to activate imines and carbonyl compounds, mimicking these enzymes to protonate simple olefins that then engage in asymmetric catalytic reactions has remained a substantial synthetic challenge. Here, we show that a class of confined and strong chiral Brønsted acids enables the catalytic asymmetric intramolecular hydroalkoxylation of unbiased olefins. The methodology gives rapid access to biologically active 1,1-disubstituted tetrahydrofurans, including (–)-Boivinianin A