SYNTHESIS, ISOLATION, AND REACTIVITY OF KINETICALLY STABILIZED AROMATIC NITROSAMIDES AND NEW LOW DIMENSIONAL ORGANIC INORGANIC HYBRID MATERIALS
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The conversion of aromatic amines to esters and phenols is a useful transformation typically carried out using diazonium salt intermediates, but the yields can vary wildly. It has been demonstrated that the reaction of aromatic amides with nitrite in a solution of acetic anhydride and acetic acid can give access to a number of functional groups including the corresponding esters. It is presumed that these transformations go through the initial formation of an intermediate N-aromatic nitrosamide which can than decompose either homolytically or heterolytically. While this reactive intermediate is potentially synthetically useful and has demonstrated to give more consistent reactivity than its related diazonium salt, much is still not known about the mechanistic behavior of these compounds with various postulated mechanisms suggesting these N-aromatic nitrosamides decompose into radicals through a variety of complex intermediates. The elucidation of this mechanistic behavior is made more difficult by the fact that N-aromatic nitrosamides are fairly reactive making their isolation and purification difficult. This makes the study of these systems in pure solvent systems difficult and in some cases impossible. In order to harness the synthetic potential of these species their mechanistic behavior must be further elucidated. In this work N-aromatic nitrosamides stabilized by the presence of steric bulk have been synthesized, isolated and characterized by NMR as well as X-ray crystallography. The reactions of these N-aromatic nitrosamides have been studied in a wide variety of solvents. These studies demonstrated that the dielectric constant of the solvent has a large degree of influence over the reaction mechanism of N-aromatic nitrosamide decomposition with higher dielectric constant solvents favoring addition of the solvent to the aromatic ring while lower dielectric constant solvents favored the formation of indazole formation in cases where cyclization was possible. These results indicate that stabilized N-aromatic nitrosamides decompose through carbocationic like intermediates in high dielectric constant solvents while neutral pathways dominate in low dielectric constant solvents suggesting that, for the stabilized nitrosamide systems presented in this work, radical reaction pathways are not present or minimal in the decomposition of these systems. Beyond the mechanistic implications established in this work the potential synthetic utility of these systems has also been established. In general, the decomposition of these stabilized N-aromatic nitrosamide systems in straight solvent environments resulted in the corresponding addition products in over 90% yield. In another of examples these N-aromatic nitrosamide systems were able to be competitive or outperform other established synthetic methods. In the case of 2,6 methyl substituted and 2,5 methyl substituted nitrosamide systems decomposition in methanol and ethanol gave the corresponding aryl ethers in over 80% yield, while decompositions of 2 methyl substituted diazonium salt in methanol and ethanol gave less than 30% of the corresponding aryl ether. The methods developed in this work also led to the synthesis of sterically hindered aryl tert-butyl ethers in over 80% yield which is directly competitive with the yields obtained from using the more difficult to prepare diaryliodonium salts (75-95% yields). The chemistry developed in this work has been applied to the post functionalization of two new cyclophane amide systems, with the goal that this chemistry could be used as a key transformation in the synthesis of redox active quinone cyclophanes. Nitrosolation and rearrangement of the anti-5,8,13,16-tetramethyl-4,7,12,15-tetraamido[2.2]paracyclophane to the anti-5,8,13,16-tetramethyl-4,7,12,15-tetraacetoxy[2.2]paracyclophane was successful but low yielding giving yields below 20% limiting the utility of this method as a route to the quinone cyclophane. The nitrosolation and rearrangement of the anti-5,8,13,16,21,24,29,32-octamethyl-4,7,12,15,20,23,28,31-octaamido[126.96.36.199]paracyclophane was found to be unsuccessful, yielding none of the desired anti-5,8,13,16,21,24,29,32-octamethyl-4,7,12,15,20,23,28,31-octaacetoxy[188.8.131.52]paracyclophane, but instead gave large complex mixtures of products that could not be resolved. NMR studies of the parent amide demonstrated that two pairs of the aryl methyl groups and two pairs of the amides were in fact pointed into the center of the macrocycle, making the nitrosolation and rearrangement of this system difficult or impossible due to the steric influence of the surrounding structure. This work has also focused on the development of low dimensional organic-inorganic hybrid structures for the development of light emitting materials. The synthesis of a series of methylated benzyl ammonium salts have been synthesized and used to fabricate low dimensional organic inorganic hybrid structures. These materials demonstrated light emission behavior with the majority of the structures behaving as broadband white light emitters. Importantly, for many of the fabricated compounds improvements in the light emitting behavior of the organic compounds were observed in the hybrid structures when compared to the light emitting properties of the free organic salts.
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