The focus of my graduate research in the Krische group has been the development of catalytic carbon-carbon bond forming reactions with an emphasis on controlling diastereo- and enatio-selectivity in transfer hydrogenative couplings. The broad goal of our research program has been the development and implementation of efficient green methods for carbonyl addition employing [pi]-unsaturates as surrogates to preformed organometallic reagents, thus enabling byproduct free variants of traditional carbanion chemistry. This dissertation shows the new reactions that I have developed toward this goal. These reactions includes new metal catalyzed approaches for carbonyl crotylation, aminoallylation, and vinylogous reformatsky aldol reactions. / text

Carbon-Carbon bond forming reactions are very important in organic synthesis. Preparation of most of the leading drugs on the market involves at least one carbon-carbon bond forming transformation. However, use of preformed oganometallics for this purpose is neither atom economical nor cost effective. Thus, development of atom economical and environmentally benign carbon-carbon bond forming methods is highly desirable. Catalytic hydrogenation is one of the most widely used transformations in the pharmaceutical and chemical industry. However, for several years the catalytic hydrogenation was limited to the carbon-carbon bond forming processes such as alkene hydroformylation and the Fischer-Tropsch reactions. In 2004 Krische group demonstrated a novel reductive aldol cyclization under rhodium catalyzed hydrogenation conditions. Following this, a variety of reductive carbon-carbon bond forming reactions were developed under hydrogenation conditions. The first chapter of this dissertation summarizes the reductive couplings of π-unsaturates to imines. N-heterocyclic compounds are very valuble in pharmaceutical and agrochemical industries. In the second chapter a variety of hydrogen mediated reductive couplings to aromatic N-heterocycles have been described. Transfer hydrogenation represents another important class of reactions in organic chemistry. This process employs hydrogen sources other than gaseous dihydrogen, such as isopropanol. Very recently, the Krische group reported a number of novel C-C coupling reactions using the concept of transfer hydrogenation. Thus, in chapter 3 a very elegant ruthenium catalyzed allylation reaction has been described. Finally, chapter 4 focuses on the reactivity of zinc enolates toward less reactive electrophiles such as allylic carbonates in the absence of any transition metal catalyst. During this process a direct allylic substitution of allylic carbonates with diorganozinc reagents has been discovered. These two transformations are conceptually very interesting. / text

Under the conditions of transfer hydrogenation employing ortho-cyclometallated iridium C,O-benzoate catalysts, two protocols of iterative chain elongation of 1,3-diols to furnish 1,3-polyols were developed. First, one-directional chain elongation employing mono-protected 1,3-diols as starting materials was achieved. In all cases, high levels of catalyst-directed enantioselectivity and diastereoselectivity were observed. Then, double asymmetric allylation of 1,n-glycols to deliver C₂-symmetric adducts with exceptional level of enantioselectivity was devised. Iterative two-directional elongation of 1,3-diols to furnish 1,3-polyols with high level of catalyst-directed diastereoselectivity was then achieved. Implementation of this methodology and other hydrogenative C-C bond formations proved to be effective means for the preparation of a known bryostatin A-ring fragment and the total synthesis of bryostatin 7. / text

Aldol reactions are widely used in forming new carbon-carbon bonds. Since the discovery of the aldol condensation, controlling the relative and absolute stereochemistry in aldol chemistry has been a major interest in organic chemistry. Efforts in achieving diastereoselectivity in aldol reactions via chelation of Lewis acids to chiral aldehydes are reviewed. The following chapters discuss the diastereoselectivities of hydrogen-mediated reductive aldol reactions. Herein, a highly diastereoselective reductive aldol coupling reactions with broad substrate scope using rhodium catalysts ligated to (2-furyl)₃P were studied. It was demonstrated that the coupling of enones with alpha-amino aldehydes proceeds with high diastereoselectivity via chelation control. The second topic deals with phosphine-mediated furan ring formation. Derivatives of furan are often found in natural products and therapeutic agents. To provide a more facile route to substituted furans, we have developed a phosphine mediated reductive cyclization of gamma-acyloxy butynoates. In this reaction, phosphine is involved in both the reductive formation of allenyl ketones from acyloxy butynoates and the subsequent catalytic cyclization. / text

No description available.

<p>Three methodology studies and two total synthesis endeavors are presented. First, a study of Lewis acid and hydrogen bond mediated soft enolization of thioesters and their addition to imines in the Mannich reaction is reported. MgBr2*OEt2 and Hunig's base are used in concert with bulky thioesters and aromatic aldehydes to generate syn-b-aminothioesters with moderate diastereoselectivity and yield. Next, a biomimetic organocatalytic Mannich reaction is presented using a chiral cinchona alkaloid to effect the enantioselective addition of an imines to thioesters with high yield and diastereoselectivity and enantioselectivities up to 88:12.</p><p>The direct addition of enolizable aldehydes to a-iodo thioesters to produce b-hydroxy thioesters enabled by reductive soft enolization is reported. The transformation is operationally simple and efficient and has the unusual feature of giving high syn-selectivity, which is the opposite of that produced in the aldol addition with (thio)esters under conventional conditions. This method is tolerant to aldehydes and imines that contain acidic a-protons, as well as electrophiles containing other acidic protons and base-sensitive functional groups.</p><p>The development of a strategy for the asymmetric synthesis of a large portion of the polycyclic polyprenylated acyl phloroglucinols via N-amino cyclic carbamate hydrazones, and its application to the first asymmetric total synthesis of both (+)- and (-)-clusianone is discussed. The clusianones are synthesized with an er of 99:1 and their anti-HIV activity is found to be 1.53 and 1.13 &#61549;M, respectively. A library of clusianone-like compounds is synthesized and their biological activity has been probed.</p><p>Finally, efforts towards the total synthesis of brasilicardin A are reported. An appropriate model system was synthesized, and conditions were established using a pinene-based aldol reaction to synthesize the b-methoxy-a-amino ester side chain of the molecule. Next, efforts toward the synthesis of the anti-syn-anti- perhydro-phenanthrene core are discussed.</p> / Dissertation

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2002. / Härtill 4 uppsatser.

Thesis (Ph. D.)--State University of New York at Binghamton, Materials Science and Engineering Program, 2009. / Includes bibliographical references.

Carbon-carbon (C/C) composites are notable among engineering materials in aerospace and defense industries possessing excellent specific mechanical, thermal, frictional and wear properties. C/C maintain their properties at temperatures where most of the high end alloys give in, and maintain their dimensional stability at temperatures above 2000 oC. C/C is frequently used in aircraft and automotive industries as brake materials. However, frictional performance is dependent on various parameters: microstructure, fiber type, fiber orientation distribution, fiber/matrix interfacial bond, heat treatment, and oxidation. The present study in dissertation provides an insight into the impact of heat treatment, and oxidation on microstructure, mechanical and thermal properties. The heat treatment (performed at 1800, 2100, 2400 oC in argon) of two-directional (2-D) pitch-fiber with charred resin carbon matrix, and three-directional (3-D) PAN-fiber with CVI carbon matrix influenced microstructure, mechanical and thermal properties. Microstructure characterized by polarized light microscopy (PLM), XRD, and Raman spectroscopy changed with increasing heat treatment temperature. The RL microstructure of 3-D C/C progressively highly organized, whereas ISO microstructure of 2-D C/C's charred resin hardly organized into an ordered structure as evident from Raman spectroscopy and Raman profiling of polished samples. Pitch-fiber organized more than the ISO microstructure of charred resin matrix. On the other, PAN-fiber became more ordered, but was organization was lower than pitch-fiber. Thermal conductivity increased for both (2-D, 3-D C/C) materials in comparison to non-heat treated (NHT) C/Cs. Thermal conductivity of oxidized samples decreased significantly than non-oxidized samples. In-plane thermal conductivity of 3-D C/C was much higher than that of 2-D C/C, and was attributed to the rough laminar (RL) microstructure of carbon matrix and continuous PAN-fiber when compared to the short pitch-fiber in isotropic (ISO) carbon matrix. Mechanical properties (tensile, compressive, shear) deteriorated with increasing heat treatment. However, statistical analysis using ANOVA showed that there was not any significant difference between the NHT and heat treated C/C materials in terms of mechanical strength, modulus, failure strain and fracture energy. The oxidized samples of heat treated (1800/2100/2400 oC) C/C materials (2-D, 3-D) showed an appreciable decrease in mechanical strength and modulus than non-oxidized samples, with progressively heat treated C/C becoming more oxidation resistant than NHT C/C. The study demonstrated a highly inhomogeneous nature of C/C, and sample size is a very important parameter in governing mechanical properties. Since, the slightest change in the dimension of samples could bring about a radically different outcome in terms of mechanical properties, and can hardly be representative of the bulk properties. Therefore, in order to obtain a good estimate of the bulk properties, the sample size must be comparable to the bulk material. The research nonetheless showed the impact of sample size in estimating the mechanical properties of bulk properties, which are highly significant after statistical analysis, and, therefore, it must be taken into account to understand the processing-structure-property-analysis relationships.

Circular air-coupled ultrasonic testing (ACUT) setup for the inspection of commercial carbon-carbon composite aircraft brake disks was developed in Intelligent Measurement and Evaluation Laboratory (IMEL) at Southern Illinois University Carbondale (SIUC). The developed test setup utilizes Airstar single channel air-coupled equipment and has only manual A-scan and B-scan capability. The developed ACUT technique is unique compared to the commercial C-scan ultrasonic systems and is proficient, fast, economically feasible, and easy to implement method particularly for the inspection of carbon-carbon (C/C) composites aircraft brake disks. Prior to conducting air-coupled measurements, wobble analysis was carried out. This was important because significant wobbling in the test setup can lead to the interference of the reflected and the incident beam which would result to inaccurate ultrasonic measurements. The measured deviation due to wobbling, surface profile of the disk, design, and experimental error were relatively small. Therefore, these errors were neglected while performing ACUT measurements. For ACUT measurements, several through-transmitted amplitude signals were recorded within the C/C brake disks manually. The images were then reconstructed using Matlab based on the through-transmitted amplitude signals. Finally, a comparison was drawn between the reconstructed images and the C-scan images of the C/C brake disks obtained from the commercial Airstar C-scan ACUT system. Like commercial C-scan ACUT image results, reconstructed images were also able to detect all defects in the commercial C/C brake disks which served for the system verification and validation. In addition, defect, non-defect, and suspected areas within the C/C brake disks were quantified with air-coupled measurement. For this, light microscopy was conducted for every sample made from each C/C brake disks at lower magnification of 10X. It was concluded that it is very difficult to assess the crack or delamination situation based on a 2D micrograph of one depth. Also, it was concluded that an internal porosity and micro-cracks may not be only factors that can be related to defects. Finally, an intelligent systems approach, specifically, fuzzy logic and artificial neural network (ANN) methodologies were implemented for the automatic defect detection in commercial C/C aircraft brake disks by using air-coupled ultrasonic results. For this, a multi-layer perceptron (MLP) with two hidden layers and a scaled conjugate gradient back-propagation (BP) learning algorithm was used for the ANN training. The network training process was performed in an off-line mode using the ANN toolbox in Matlab. The network training was repeated until a steady state was reached, where there was no further change in the synaptic weights. The ANN provided plausible results in detecting the defect areas for different C/C brake disks. It was also demonstrated that the system was able to learn the rules without knowing any algorithm for automatic defect detection.