Wonsuk Kim

Unification of Anion Relay Chemistry with the Takeda and Hiyama Cross-Coupling Reactions: Identification of an Effective Silicon-Based Transfer Agent

The unification of Anion Relay Chemistry (ARC) with the Takeda and Hiyama palladium-mediated cross-coupling processes to provide aryl-aryl, alkenyl-aryl, and alkenyl-alkenyl coupled products by exploiting a common silicon-based transfer agent has been achieved. These results provide a practical solution for intermolecular cross-coupling of organolithium reagents without the problematic lithium-halogen exchange and/or undesired homocoupling that has kept organolithium cross-couplings from achieving the same level of utility asother palladium-mediated methods (e.g., Suzuki organoboron, Negishi organozinc, Stille organotin, Kumada organomagnesium, etc.).

Diversity-oriented synthesis leads to an effective class of bifunctional linchpins uniting anion relay chemistry (ARC) with benzyne reactivity

In conjunction with the construction of a diversity-oriented synthesis library of 10-membered ring “natural product-like” macrolides, the design, synthesis, and validation of a unique class of bifunctional linchpins, uniting benzyne reactivity initiated by type II anion relay chemistry (ARC) has been achieved, permitting access to diverse [2+2], [3+2], and [4+2] cycloadducts.

Diversity-oriented synthesis of 2,4,6-trisubstituted piperidines via type II anion relay chemistry.

An effective, general protocol for the Diversity-Oriented Synthesis (DOS) of 2,4,6-trisubstituted piperidine congeners has been designed and validated. The successful strategy entails a modular approach to all possible stereoisomers of the selected piperidine scaffold, exploiting Type II Anion Relay Chemistry (ARC), followed in turn by intramolecular S(N)2 cyclization, chemoselective removal of the dithiane moieties and carbonyl reductions.

Harmonic balance/Galerkin method for non-smooth dynamic systems

Models of non-linear systems frequently introduce forces with bounded continuity resulting in non-smooth (even discontinuous) flow. Examples include systems with clearances, backlash, friction, and impulses. Asymptotic methods require smooth (differentiable) flow and are therefore ill-suited for analyzing non-smooth systems. In these cases, the traditional harmonic balance method may be used to obtain approximate periodic solutions, but the method suffers from extremely slow convergence in general. Generalizations of the traditional harmonic balance method are introduced in this paper that result in superior convergence rates and superior modes of convergence. These improvements derive from the introduction of one or more expansion functions that possesses the same degree of continuity as the exact solution. In particular, forming an infinite series of such functions results in an expansion in the same function space of the exact solution. This expansion converges pointwise to the exact solution and to all derivatives thereof. These improvements are illustrated by example upon re-evaluating a classical single degree-of-freedom model for friction-induced vibration.

Uniting anion relay chemistry with Pd-mediated cross coupling: design, synthesis and evaluation of bifunctional aryl and vinyl silane linchpins.

Union of type II Anion Relay Chemistry (ARC) with Pd-induced Cross Coupling Reactions (CCR) has been achieved, in conjunction with the design, synthesis, and evaluation of a new class of bifunctional linchpins, comprising a series of vinyl silanes bearing beta- or gamma-electrophilic sites. The synthetic tactic permits both alkylation and Pd-mediated CCR of the anions derived via 1,4-silyl C(sp(2))-->O Brook Rearrangements.

Stille couplings of 3-(trimethylstannyl)-5-bromo-2-pyrone for the syntheses of 3-aryl-5-bromo-2-pyrones and their ambident dienyl characters

Abstract 3-(Trimethylstannyl)-5-bromo-2-pyrone underwent facile Stille coupling reactions with aryl halides to produce various 3-substituted 5-bromo-2-pyrones. The resulting 3-aryl-2-pyrone derivatives underwent both normal and inverse electron demand D-A cycloadditions depending on the type of the dienophiles being reacted.

High strain-rate behavior of natural fiber-reinforced polymer composites:

The high strain-rate constitutive behavior of polymer composites with various natural fibers is studied. Hemp, hemp/glass hybrid, cellulose, and wheat straw-reinforced polymeric composites have been manufactured, and a split-Hopkinson pressure bar apparatus has been designed to measure the dynamic stress–strain response of the materials. Using the apparatus, compressive stress–strain curves have been obtained that reveal the materials’ constitutive characteristics at strain rates between 600 and 2400 strain/s. Primary findings indicate that natural fibers in thermoset composites dissipate energy at lower levels of stress and higher strain than glass-reinforced composites. In the case of thermoplastic matrices, the effect on energy dissipation of natural fibers vs. conventional talc reinforcements is highly dependent on resin properties. Natural fibers in polypropylene homopolymer show improved reinforcement but have degraded energy dissipation compared to talc. Whereas in polypropylene copolymer, natural fibers result in improved energy dissipation compared to talc. These data are useful for proper design, analysis, and simulation of lightweight biocomposites.

Multicomponent type II anion relay chemistry (ARC): one-pot syntheses of 2,3-disubstituted furans and thiophenes.

Effective, one-pot syntheses of 2,3-disubstituted furans and thiophenes, exploiting 2-tert-butyldimethylsilyl-3-formylfuran and -thiophene as the respective bifunctional linchpins, have been developed. The synthetic protocol involves multicomponent type II Anion Relay Chemistry (ARC) mediated by a solvent-controlled C(sp(2))-->O 1,4-Brook rearrangement. Simple organolithiums and alpha-disubstituted ester enolates prove effective as the initiating nucleophiles.

Free in-plane vibration of an axially moving membrane

The free in-plane vibration of an axially moving membrane is studied considering the effects of both the translating speed and aspect ratio of the membrane. Two sets of boundary conditions, which are free and fixed constraints in the lateral direction at boundaries with mass transport, are discussed in this study. From the extended Hamilton principle, the coupled equations of the longitudinal and lateral motions are derived. These equations are then discretized by using the Galerkin method. From the discretized equations, the natural frequencies and mode shapes are obtained for the variations of the translating speed and aspect ratio. The results show that the translating speed, aspect ratio, and boundary conditions have significant effects on the in-plane vibrations of the moving membrane.

Regioselective Stille coupling reactions of 3,5-dibromo-2-pyrone with various aryl and vinyl stannanes

Abstract 3,5-Dibromo-2-pyrone underwent facile regioselective Stille coupling reactions with aryl, heteroaryl and vinyl stannanes to produce various 3-substituted, 5-bromo-2-pyrones. Addition of a catalytic amount of CuI greatly increased the selectivity and chemical yield of the desired 3-aryl-5-bromo-2-pyrone. Second Stille coupling reactions on the resulting 3-aryl-2-pyrones gave rise to a series of potentially useful 2-pyrones with two different functionalities at C3 and C5 position in good to excellent isolated yields. 2-Pyrones with pyridyl groups at C3 position can undergo Lewis acid catalyzed Diels–Alder cycloaddition reactions with benzyl vinyl ether.