Development of novel catalytic asymmetric diborylation methodologies

This thesis describes the study of the β-borylation reaction on different types of electron deficient substrates as well as the application of the methodologies herein developed into the synthesis of a key intermediate for cholesterol-lowering drug Atorvastatin. Within the frame of the use of organoboron compounds in organic synthesis, the literature review presented in the first section after a brief introduction on organoboranes is focused on the different strategies for their synthesis via boron addition, specially the β-borylation reaction. Different aspects of the reaction are covered; enantioselective version, the different methodologies reported for the activation of the diborane reagents or organic electron deficient substrates. Within the study of the β-borylation reaction on α,β-unsaturated aldehydes via the in situ generated amine-derived aldimine intermediates, and the further application of these synthetically attractive compounds, the relevant challenge of handling β-boryl aldehydes was met. It was confirmed that this type of compound was indeed unstable especially under chromatographic purification conditions, leading to de-borylation. In addition, mechanistic studies were carried out in order to achieve a better understanding of the whole process, but it was not possible to clarify it and avoid the undesired side-process. Hence, the establishment of an efficient derivatisation methodology was required. The solution consisted of a mild, efficient derivatisation process involving an in situ copper(II) sulfate-based imine hydrolysis followed by Wittig trapping of the resulting aldehyde. Further exploitation of homoallylic boronate carboxylate esters as substrates for a second borylation reaction, led to obtaining versatile 1,3-diborylated esters. A novel methodology was developed which allowed the control of the asymmetry induced in the new stereogenic centre created for a range of substrates, due to the presence of the two boryl units which could subsequently be transformed into other functionalities leading to building blocks for the synthesis of multi-functional, chiral compounds. Therefore, the two boryl units were then examined for transformation into functionalities which would allow unambiguous stereochemical assignment of the two borylation reactions. Specifically, an oxidation/acetal formation sequence was examined showing that 6-membered ring acetonide acetals were ideal compounds for this purpose. Beside aiding the stereochemical analysis, it was confirmed that this dual asymmetric borylation methodology was useful for the synthesis of 3,5-dihydroxy acids (or esters analogous) side-chain present in many natural products or drugs, such as statin-type drugs. Complementarily, and with the aim of expanding the type of substrates for the β-borylation reaction, structurally varied compounds were examined. Firstly, substrates presenting an additional unsaturation were evaluated under the imine formation/β-borylation reaction sequence conditions paying special attention to the 1,4- vs 1,6-addition selectivity, were examined as a possible alternative for the synthesis of diborylated compounds in a direct manner. This was followed by the study of different unsaturation, and in particular, an alkyne instead of an alkene, i.e. α,β-acetylenic carbonyl compounds, which were envisioned as ideal platforms for the synthesis of vinyl boronates. As well as a brief study on the β-borylation reaction on β-enamino ester substrates which could a priori give rise to valuable α-amino boronate compounds, is reported

Straining Definitions

The concept of strain is ubiquitous in engineering textbooks. It is defined early in engineering education as change in length divided by initial length, and is used to quantify deformations due to things like stresses and temperature changes. The concept itself is quite straightforward and represents homogenous materials well, but homogenous materials are rarely present in engineering design. Composite materials such reinforced concrete cannot be simply defined, as their properties are heavily influenced by their non-uniformity. For example, there are large deformations around tensile cracks in reinforced concrete, where the reinforcement withstands all the tensile stress, and little deformation in uncracked regions. How should tensile strain in reinforced concrete be measured? Industry mandates that steel reinforcement samples be tested using a gage length of 8 inches on a region that includes fracture, but do these measurements portray the in situ tensile behavior of reinforced concrete? This project addresses the deceivingly simple question of what gage length to use with reinforced concrete to reconcile results from testing samples of the individual elements of reinforced concrete. The project subjects rebars encased in rectangular concrete prisms to uniaxial tension, and then uses 3d optical point tracking (e.g. Optotrak) and Digital Image Correlation (DIC) to monitor deformations. The deformations at failure are then analyzed using different gage lengths to calculate the strain occurring between two points. It was found that gage lengths greater than 6 times the average crack spacing showed converging tensile strains

Drift Capacity of Structural Walls with Lap Splices

Twelve large-scale reinforced concrete specimens with lap splices in the longitudinal reinforcement were tested at Purdue University’s Bowen Laboratory to produce data to evaluate the deformability of structural walls with lap splices at their base. Previous work on lap splices has focused mainly on splice strength. But in consideration of demands requiring structural toughness (e.g. blast, earthquake, differential settlement), deformability is arguably more important than strength.To obtain data on splice deformability and to study the response of lap splices in conditions more representative of those occurring in structural walls, eight specimens were tested under four-point bending and four additional specimens were tested as cantilevers under constant axial force and cyclic reversals of lateral displacement. All specimens failed abruptly by disintegration of the lap splice regardless of how the loading was controlled or what detailing was used. Large numbers of loading cycles in the linear range of response did not seem to have an appreciable effect on splice deformability. For structural walls with lap splices comparable to those tested, the observations collected suggest that drift capacity can be as low as 0.5% for splices with minimum cover, minimum transverse reinforcement terminating in hooks, and lap splice lengths selected to reach yielding in the spliced bars. That is, splice failure can occur as yield is reached or soon after. For lap splices 1.3 times longer, drift ratio at splice failure is projected to increase to approximately 0.75% or more. For cover twice as large and transverse reinforcement that is continuous around the lap splice, drift capacity is projected to increase to nearly 1% for splices designed to yield and 1.5% or more for lap splices 1.3 times longer.The evidence gathered suggests that lap splices with minimum cover and confined only by minimum transverse reinforcement terminating in hooks should not be used in applications requiring toughness in structural walls

Seismic Vulnerability Assessment of Low-Rise Reinforced Concrete Buildings in Kathmandu, Nepal

In seismically active cities like Kathmandu, there often exists a need to assess the seismic vulnerability of a large number of poorly designed buildings within a short period of time. Traditional analysis techniques do not work because they require building data that are either inaccurate or unavailable. One alternative to traditional analysis techniques is to use simple correlations like the Priority Index. This index uses basic building information such as floor area, column area, and wall area to estimate the seismic vulnerability of a building. Following the 2015 Nepal earthquake, 146 low-rise reinforced concrete buildings were surveyed in Kathmandu, Nepal. All data collected were made publicly available on DataHub (datacenterhub.org/resources/238). Indices such as the Wall Index (WI) and the Column Index (CI) were computed for each surveyed building and compared to index values obtained from similar surveys conducted in Turkey and Haiti. A plot of WI versus CI showed that 92% of all the points representing buildings with severe damage are bound by a line drawn from 0.2% WI to 0.4% CI. If this line is used as a threshold to identify the most vulnerable structures, 91% of the buildings surveyed in Kathmandu would have been classified as such. The indices used also showed good correlation with observed damage levels in Kathmandu. This correlation between vulnerability estimates and observed damage levels suggests that Priority Index can be used as a rapid and cost effective analysis tool to rank low-rise reinforced concrete buildings in terms of seismic vulnerability

The Collapse of the Alto Río Building during the 27 February 2010 Maule, Chile, Earthquake

This is the published version. Copyright 2012 Earthquake Engineering Research InstituteThe Alto Río Building, a 15-story building located in Concepción, Chile, collapsed during the 2010 Maule earthquake. Construction of the building was completed in 2009 following the Chilean building code of 1996. The building was provided with reinforced concrete structural walls (occupying nearly 7% of the floor area) to resist lateral and vertical loads. The walls failed in the first story, causing the overturning of the entire building. This paper provides detailed field observations and discusses plausible causes of the collapse

High Strength Steel in the Reinforced Concrete Structures: Serviceability

The use of high-strength steel (yield stress larger than 100 ksi) in reinforced concrete structures can provide an effective alternative to using conventional steel (yield stress up to 80 ksi). The goal of this study is to investigate if slabs with reduced quantities of high-strength steel reinforcement meet the serviceability criteria. Instantaneous and long-term deflections in slab specimens with conventional steel and reduced amounts of high-strength steel (as compared with conventional steel) were studied. Two sets of two reinforced concrete slabs, each 14 ft. long, 30 in. wide, were built. The depth, quantity, and type of longitudinal reinforcement were varied between specimens in each set. The first set of slabs consisted of a 4 in. thick specimen with conventional steel (Gr. 60) and a 6 in. thick specimen with high-strength steel (Gr. 120). The longitudinal reinforcement ratios were 0.7% and 0.2% respectively. The second set consisted of a 5 in. thick specimen with Gr. 60 steel and an 8 in. thick specimen with Gr. 120 steel. The longitudinal reinforcement ratios were 0.5% and 0.1% respectively. The slabs were designed such that the theoretical deflections at service loads were similar for the specimens within each set. The slabs will be loaded until the working strains are reached in the reinforcement, and then will be tested under this constant service-load

Strength of Reinforced Concrete Beams with High-Strength Steel

Structures are commonly made of reinforced concrete, which is a composite material made of concrete and steel reinforcement. Using high-strength steel, with yield stress larger than 100 ksi, could help reduce the quantity of steel required in structural members, thus reducing costs and improving constructability. The hypothesis being tested is that smaller quantities of high-strength steel reinforcement (HSSR) can be used in place of conventional steel in reinforced concrete beams while maintaining similar strength and deformation at failure. Two reinforced concrete beams with two different types of longitudinal steel reinforcement were constructed. The beams were 18 in. wide, 30 in. deep and 58.5 ft long. The beam with HSSR had approximately half the quantity of longitudinal reinforcement leading to reduced material costs and simpler construction. Numerical analyses indicate that the two beams will have comparable strengths and deformation capacities indicating that conventional steel can be replaced by HSSR

Current jumps in flat-band ladders with Dzyaloshinskii-Moriya interactions

Localized magnons states, due to flat bands in the spectrum, is an intensely studied phenomenon and can be found in many frustrated magnets of different spatial dimensionality. The presence of Dzyaloshinskii-Moriya (DM) interactions may change radically the behavior in such systems. In this context, we study a paradigmatic example of a one-dimensional frustrated antiferromagnet, the sawtooth chain in the presence of DM interactions. Using both path integrals methods and numerical Density Matrix Renormalization Group, we revisit the physics of localized magnons and determine the consequences of the DM interaction on the ground state. We have studied the spin current behavior, finding three different regimes. First, a Luttinger-liquid regime where the spin current shows a step behavior as a function of parameter D, at a low magnetic field. Increasing the magnetic field, the system is in the Meissner phase at the m = 1/2 plateau, where the spin current is proportional to the DM parameter. Finally, further increasing the magnetic field and for finite D there is a small stiffness regime where the spin current shows, at fixed magnetization, a jump to large values at D = 0, a phenomenon also due to the flat band.Fil: Acevedo, Santiago Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Pujol, P.. Université Paul Sabatier; Francia. Université de Toulouse; FranciaFil: Lamas, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Failure mechanism of reinforced concrete structural walls with and without confinement

This paper presents the results of cyclic loading tests on two large-scale reinforced concrete structural walls that were conducted at Purdue University. One of the walls had confinement reinforcement meeting ACI-318-11 requirements while the other wall did not have any confinement reinforcement. The walls were tested as part of a larger study aimed at indentifying parameters affecting failure modes observed to limit the drift capacity of structural walls in Chile during the Maule Earthquake of 2010. These failure modes include out-of-plane buckling (of the wall rather tan individual reinforcing bars), compression failure, and bond failure. This paper discusses the effects of confinement on failure mode. Distributions of unit strain and curvature obtained with a dense array of non-contact coordinate-tracking targets are also presented