Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007. / Committee Chair: Prof. Charles L. Liotta; Committee Member: Prof. Arthur J. Ragauskas; Committee Member: Prof. Charles A. Eckert; Committee Member: Prof. John D. Muzzy; Committee Member: Prof. Rigiberto Hernandez.

The chemical reactivity of a solid is influenced to a marked degree by the presence of imperfections or defects in the solid. Bond strengths are considerably weaker at points of imperfection than elsewhere in the solid, and hence the initiation of reaction is favoured at these sites due to the relative ease of bond rupture. Line defects, such as edge or screw dislocations, jogs, Smekul cracks etc, are of prime importance in such changes. The surface of a solid or in intergranular boundaries, where a state of strain exists, are also favourable places for the initiation of a reaction, Point defects e.g. vacancies or interstitialions or atoms also play important roles in chemical change, often in conjuction with line defects.

Athanasios Markos Abstract This Thesis deals with denitrogenative transformations of N-fluoroalkyl-1,2,3-triazoles, easily available heterocycles via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) of safe and stable N-fluoroalkyl azides and alkynes. The introductory chapter describes general approaches towards N1-substituted 1,2,3- triazoles, methods of N1-,-difluoroalkyl-1,2,3-triazoles preparation and both, transition metal-catalyzed and transition metal-free transformations of N1-substituted 1,2,3- triazoles. In the first part of the Thesis, rhodium-catalyzed reactions of N-fluoroalkyl-1,2,3-triazoles are described. Rhodium-catalyzed reactions of N-fluoroalkyl-1,2,3-triazoles in presence of suitable reagents provide access to five-membered N-fluoroalkyl heterocycles, 2- fluoroalkyl oxazoles and ketamides. In the second part of the Thesis, both Brønsted and Lewis acid-mediated transformations of N-fluoroalkyl-1,2,3-triazoles leading to stereodefined N-alkenyl compounds, such as enamides, enimines, amidines and other are discussed. The robustness of the method is showcased on gram scale syntheses and preparation of a drug analogue. At last, thermally-induced rearrangement of N-fluoroalkyl-1,2,3-triazoles to 3-fluoroalkyl-2H- azirines and the proposed mechanism of the reaction are described.

The incorporation of the trifluoromethyl and perfluoroalkyl motifs into organic compounds has been a hot topic in synthetic organofluorine chemistry. There is a plethora of methods for the introduction of the CF3 moiety at carbon, oxygen and sulfur centers. In sharp contrast, methods for synthesizing N-trifluoromethyl and N-perfluoroalkyl compounds are very limited and new approaches are highly sought-after. The scarcity of these compounds prompted us to develop reagents capable of transferring the perfluoroalkyl unit to nitrogen atom. To fulfil this purpose, we have regarded azidoperfluoroalkanes as ideal reagents, therefore, this thesis is concerned with the synthesis and applications of these azides. The first part describes the preparation of azidoperfluoroalkanes. Upon activation by cesium fluoride, TMSCF3 transfers the trifluoromethyl group to an electrophilic azide to produce the desired azidotrifluoromethane. Longer carbon chain azidoperfluoroalkanes were prepared in a similar way, starting from the corresponding organosilane. A different synthetic strategy was applied for the preparation of azidopentafluoroethane where the perfluoroalkyl anion was generated from pentafluoroethane with n BuLi, followed by the addition of tosyl azide. The isolation of these fluorinated azides was...

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Thesis advisor: X. Peter Zhang / Highly strained three membered heterocycles are a common motif in many biologically relevant molecules and represent a versatile building block for organic synthesis. Of special interest for asymmetric synthesis is the construction of enantioenriched aziridines and epoxides, which are often used as chiral synthons to introduce heteroatoms in a stereoselective fashion. Among different elegant strategies, the direct aziridination and epoxidation of the ubiquitous alkene functionality represents one of the most powerful methods to access these motifs. Given the synthetic importance of the enantioenriched smallest aza- and oxaheterocycles, the focus of this dissertation is centered on the design and use of chiral cobalt porphyrins as catalysts to develop new methodologies for the asymmetric radical aziridination and epoxidation of alkenes.In the first part of this dissertation, we focused on using carbonyl azides as nitrogen source for the enantioselective radical aziridination of alkenes. Despite its high functionality and versatility for further derivatization, carbonyl azides have never been reported as nitrogen source for intermolecular asymmetric alkene aziridination. In the second part of this dissertation, we focused on opening up a new area of research, which involves the generation and characterization of the unprecedented cobalt porphyrin-supported oxygen-centered radical species. Finally, we demonstrated the synthetic utility of these new radical species by developing a new system for the asymmetric epoxidation of alkenes through the design and development of a novel family of catalyst named “JesuPhyrin”. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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The generality of the [4+1] annulation methodology in the context of natural product synthesis was demonstrated by extending its applicability to the heteroatom (nitrogen) case thus allowing access to the alkaloid field. This novel methodology involved the intramolecular union of a hypovalent nitrogen atom equivalent and a conjugated diene to afford a pyrroline ring. The flexibility of this strategy was exemplified by the formal synthesis of ring-A oxygenated pyrrolizidine alkaloids platynecine 8, turneforcidine 9, hastanecine 10, and dihydroxyheliotridane 11. The key features of this technology involved preparation of azidodiene ill, its cyclization, via the intermediate triazoline which was not isolated, to vinylaziridines 234, and the vinylaziridine-pyrroline rearrangement of several derivatives of 234 to pyrrolizidines 239, 241, and 242. A study of the thermal decomposition of oxygenated azidodienes such as 196 and 233 was carried out. Conclusive results regarding the stereochemical control of the C-7 substituent were attained and used for the formal stereospecific syntheses of pyrrolizidinediols 8, 9, 10, and 11. The possibility of asymmetric induction was also investigated, and was realized in the microbial reduction of only one of the enantiomers of alcohol ill protected as ester 248, providing potential access to either enantiomeric series of pyrrolizidine diols. [see document for diagram of chemical reaction] / Ph. D.

The reaction of sodium azide with 2-p-chloro- and 2-p–methoxyphenyl–3,4,5-triphenyl–2,4-cyclopentadien– Iâ one was studied to determine if the substituent would have any appreciable effect on the product distribution of the corresponding l,5,7,8–tetraphenyl-2,3,4–triazabicyclo[3.3.0]octa-2,7-dien-6-ones and the 3,4,5,6–tetraphenyl–2(lH)â pyridinones that were formed by an acid catalyzed rearrangement. It was found that the chloro substituent had no effect on the reaction. The methoxy substituent had a moderate effect in that the product arising from the stabilized intermediate cation was favored by a ratio of approximately 3 to l. The two simple linear analogs studied were l,2,3,3–tetraphenyl-2-propen-l-one and 3,4,4-triphenyl-3–buten–2â one. These compounds did not react with azide, presumably due to charge delocalization. Also studied as a cyclic analog was 2,7-diphenyltropone which did not react due to the aromatic character of the tropone ring system. A reaction did occur with diphenylcyclopropenone to give an unidentified product. However, the reaction did not take place in the same fashion as for the tetracyclones. / Master of Science