No description available.

Thesis advisor: Jeffrey A. Byers / Chapter 1: There are a limited number of examples of metal-catalyzed Brook rearrangements in the literature, none of which involve ruthenium, rhodium, or iridium which are common ketone hydrogenation catalysts. The content of this chapter introduces the traditional Brook rearrangement and its advantages and disadvantages in chemical synthesis. Furthermore, the few examples of metal-catalyzed Brook rearrangements of acylsilanes and structurally similar moieties are discussed. Chapter 2: Utilizing a Brook rearrangement under hydrogenation or transfer hydrogenation conditions opens up a new area of catalytic reactivity that has not been fully explored. To our knowledge, metal complexes based on ruthenium and rhodium have never been shown to catalyze a Brook rearrangement of acylsilanes. This chapter describes the mechanistic implications of a Brook rearrangement under hydrogenation or transfer hydrogenation conditions as well as the first example of a ruthenium-catalyzed Brook rearrangement of aryl acylsilanes. Chapter 3: Pioneering work performed by Jeffrey Johnson and co-workers in the area of catalytic coupling of acylsilanes and various electrophiles showed that formation of new C-C bonds through a Brook rearrangement can be a powerful synthetic tool. In this chapter, we investigate an intermolecular coupling of aryl acylsilanes and aldehydes through a metal-catalyzed Brook rearrangement under transfer hydrogenation conditions to yield two synthetically useful motifs, specifically oxygenated bicyclic compounds. A reaction screen was performed on the coupling capabilities of these two species with various ruthenium and rhodium catalysts. The result of the screen was synthesis of a silyl ether acetal through employing the starting material as the reducing equivalent. Additionally, mechanistic insight was gained to further develop the proposed methodology. Chapter 4: An intramolecular approach to achieving coupling of acylsilanes and many different types of electrophiles was envisioned as a way of furnishing synthetically useful bicyclic compounds in one step. The focus of this chapter is the synthesis of a novel acylsilane that we proposed could undergo an intramolecular cross coupling reaction under transfer hydrogenation conditions. The conclusion of this chapter outlines the future direction of the project, which entails a new route to an intermolecular cross coupling of acylsilanes and various electrophiles. Published work from Michael Krische's laboratory helped us envision a different type of acylsilane, specifically an α,β-unsaturated acylsilane, in which binding to a metal center would proceed through a π-allyl intermediate. Ongoing efforts in the coupling of α,β-unsaturated acylsilanes with electrophiles are currently underway. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Oxonium ylides are highly reactive intermediates that can be used for the synthesis of heterocyclic and carbocyclic frameworks. These putative intermediates are almost exclusively formed from diazocarbonyl derived metallocarbenes, by attack of a pendent oxygen atom. Oxonium ylides have been shown to furnish products derived from the [1,2]-shift (Stevens rearrangement) or the [2,3]-shift in an efficient manner. Chapter 1 is a review of oxonium ylides in synthesis focusing on factors that influence the reactivity of these intermediates. Previous work has shown that the sulfur-directed Stevens rearrangement is an efficient reaction for the generation of seven and eight-membered oxa-bridged carbocycles fused to five-membered rings. Chapter 2 describes an extension of this chemistry where six-seven and six-eight membered oxa-bridged carbocyclic products were furnished in good yields. The chemo- and diastereoselectivity of these rearrangements was dependent on the configuration of the acetal stereocentre present in the diazoketone precursor. A novel approach towards the synthesis of the tigliane and daphnane diterpenes is described in Chapter 3. The tricyclic framework was generated from a highly stereoselective oxygen-directed Stevens rearrangement of an oxonium ylide. This methodology provides a straightforward route to the construction of the five-seven-six ring system found in these classes of natural products. Finally, the sulfur-directed Stevens [1,2]-shift was employed in an attempted total synthesis of the natural product (+)-phorbol in Chapter 4. Several variations of the original synthetic scheme were examined, in an effort to construct the core 6-7 ring structure. The Stevens rearrangement was found to provide the 6-7 ring system of phorbol in excellent yield. The chemo- and diastereoselectivity of this rearrangement was dependent on the configuration of the acetal centre as well as the conformation of the six-membered ring in the starting material. In the future, this advanced intermediate could be used to achieve the total synthesis of (+)-phorbol.

A B S T R A C T V2O5/SnO2 solid acid catalysts have been employed for the vapour-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. Catalysts with different vanadia loading (3–15 wt%) were prepared by impregnation method and characterized by XRD, BET surface area, FTIR and 51V NMR techniques. The surface acidic properties were determined by temperature programmed desorption and cumene cracking reaction. Under optimized reaction conditions, catalyst with 9 wt% V2O5 gives the maximum amount of desired product (yield 78.8%). However, the catalysts are susceptible for deactivation due to the basic nature of the reaction products (50% deactivation in 5 h). A good correlation was obtained among the rearrangement activities of V2O5/SnO2 catalysts, their weak plus medium acidities (usually of the Bro¨ nsted type) and structural properties.

No description available.

Thesis (Ph.D)--Bowling Green State University, 2006. / Document formatted into pages; contains xv, 366 p. : ill. Includes bibliographical references.

No description available.

No description available.

The self-regeneration of stereocenters via stereolabile axially-chiral intermediates (SRSvSACI) is a synthetic strategy in which the configuration of a starting material, possessing only a single stereocenter, directs the formation of a chiral axis in an intermediate. The reaction proceeds stereospecifically, although the original stereocenter is destroyed through trigonalization. This is due to the stereochemical information encoded in the chiral axis, which is transformed into the configuration of a stereocenter in the product. In this research, we investigate the generation of axially chiral intermediates arising from both (S)-methyl lactate derivatives and 1,4-benzodiazepin-2,5-dione derivatives. For the deprotonation/alkylation of O-Bn and O-TBS substituted (S)-methyl lactate derivatives containing achiral oxazolidinones, we hypothesized that a twisted amide enolate featuring a chiral C(O-)-N axis could sufficiently impart stereochemical information and control the selectivity of the reaction. Previous work completed by Kobayashi showed in related compounds (E)- vs (Z)-enolate formation could be controlled through the identity of the 2'-oxygen substituent with –Bn affording the (E)-enolate and –TBS affording the (Z)-enolate. We investigated the utilization of achiral oxazolidinone moieties to selectively generate axial chiral intermediates that could then control the facial selectivity of sequential alkylations. Unfortunately, unforeseen synthetic difficulties prevented successful accomplishment of our project goals. We also utilized axially chiral intermediates in the generation of 3,3-disubstituted quinolone-2,4-diones. The target compounds serve as potentially useful drug scaffolds, yet synthetic access to them has remained limited due to the lack of commercial availability of the corresponding enantiopure quaternary substituted amino acids. Prior work in the Carlier group demonstrated the preferential (M)-conformer deprotonation demonstrated by 1,4-benzodiazepin-2,5-diones, and through the installation of an N4-tert-butyloxycarbonyl protecting group, we were able to take advantage of this preferential (M)-conformer deprotonation and generate 3,3-disubstituted quinolone-2,5-diones through an acyl-amino variant of the Chan rearrangement. In general, these reactions were highly enantioselective proceeding with little to no loss of enantiomeric excess. Finally, we collaborated with Professor Bloomquist to test the topical toxicity of selected ring-contracted products against adult Anopheles gambiae, the African vector of malaria. / Ph. D.

The dissertation describes Pd0-catalyzed formal 1,3-diaza-Claisen rearrangement and the design and development of cationic 1,3-diaza-Claisen rearrangement. Our previous work has shown that isocyanates react with azanorbornenes and azabicyclo[2.2.2]octenes under thermal conditions to afford zwitterionic intermediates that undergo a thermal 1,3-diaza-Claisen rearrangement to give both ureas and isoureas. However, some azanorbornenes and azabicyclooctenes failed to rearrange or proceeded in low yields. To address these challenging substrates for the thermal 1,3-diaza-Claisen rearrangement, we have developed a Pd0-catalyzed formal 1,3-diaza-Claisen rearrangement. Interestingly, under Pd0-catalyzed condition, both isocyanates with electron-withdrawing groups and isocyanates without electron-withdrawing groups react with azanorbornenes and azabicyclo[2.2.2]octenes to provide ureas as the only products in high yields. More importantly, the reactions that failed under thermal conditions were all successful under Pd0-catalysis. In addition to azanorbornenes and azabicyclo[2.2.2]octenes, other ring systems were also investigated. Pd0 catalysis has broadened the scope of tertiary allylic amines that react with isocyanates to afford 1,3-diaza-Claisen rearrangement products. In the presence of p-TsCl and NEt3, allylaminopropyl benzyl ureas were initially dehydrated to form protonated carbodiimides whose presence was confirmed by the infrared absorption frequency at 2100 cm-1 which is the characteristic band of -N=C=N-; then the in situ generated protonated carbodiimides were poised for further cationic 1,3-diaza-Claisen rearrangement to afford synthetically challenging guanidines. The effect of acid on the rearrangement was ascertained by the fact that no rearrangement product was observed by simply heating free base carbodiimide 3.10 in benzene at reflux. Other dehydration reagents, such as Tf2O, Ts2O, MsCl were also investigated, and none of them provide satisfactory results. A selection of allyamino benzyl ureas with different tether length, substituents, or in varied ring systems, were synthesized to explore the scope of this methodology. This methodology works best at allylaminopropyl benzyl ureas, and the substituents on the benzyl group does not seem to affect the reaction rate in a significant way.