No description available.

When multiple hydrogen bonds lie in-plane and parallel to each other in close proximity, they experience additional positive or negative secondary electrostatic interactions. When a pair of molecules are arranged such that every hydrogen bond acceptor is on one molecule and every hydrogen bond donor is on another, the positive secondary electrostatic interactions are maximised, and thus the association constant of the complex is enhanced. This thesis will present the development of a family of quadruple hydrogen bonded complexes containing only positive secondary interactions, which confers unprecedented stability. The complexes are sufficiently stable to maintain strong binding in polar solvents such as acetonitrile and can be switched “on” and “off” with acid and base. They will be developed into synthons for acid-base responsive supramolecular recognition, for use in stimuli-responsive supramolecular polymers and gelators.

No description available.

No description available.

Design of selective non-covalent binding systems for chemical and biological recognition requires an intimate understanding of the factors that control the strength of each interaction. Weak interactions such as anion-Π, Π-Π, and CH-Π are understood to be important contributors to the overall binding of ligands, however, these interactions are almost purely electrostatic. Aryl CH hydrogen bond donors are a recent addition to the field and provide new possibilities by introducing a partial covalent character, which imparts greater directionality and acceptor preference. CH hydrogen bonds, and other similar weakly polarized donors, are an exciting development in supramolecular chemistry because of their ubiquity, stability and structural diversity. The use of experimental and computational techniques in this dissertation has provided us with a new understanding of the energetic factors that control CH hydrogen bond strength and selectivity for anion binding. 2,6-bis(2-anilinoethynyl) receptors with an aryl CH donor as the central arene act as anion receptors with one CH hydrogen bond and four supporting NH hydrogen bonds around a semi-preorganized pocket. The scaffold provides an efficient route to substitution para to the donor, which allows for tuning of optoelectronic properties and the measurement of linear free energy relationships (LFERs) on anion binding. Association constants with anions, Cl^-, Br^-, I^-, NO3^-, were measured by ¹H NMR and UV-vis spectroscopy in water saturated chloroform. The solution data was combined with calculated and empirical measurements to provide LFERs and identify an anion dependent substituent character. The importance of substituent resonance or inductive character has been further probed by measuring the isotope effect of selective monodeuteration. Solution measurement of a normal equilibrium isotope effect points to the role of covalency in this non-traditional hydrogen bond. The application of this new understanding to developing fluorescent probes for biological and environmental anions is demonstrated with a small receptor array. This dissertation includes both previously published and unpublished co-authored material.

Over the past decade, the field of photoredox catalysis has garnered increasing amounts of attention in the organic chemistry community due to its wide applicability in sustainable free radical-mediated processes. Several examples have demonstrated that under carefully optimized conditions, efficient and highly selective processes can be developed through excitation of a photosensitizer using inexpensive, readily available light sources. Furthermore, these reactions can generally be performed under milder conditions than thermal reactions, as all the energy required to overcome the reaction barrier is supplied by light. Despite all these recent advancements in the field, many of these discoveries often lack in depth investigations into the excited state kinetics and underlying mechanisms. Furthermore, the vast majority of these transformations are photocatalyzed by ruthenium and iridium polypyridyl complexes. Not only are these precious metal catalysts extremely costly, but these metals are also known to be toxic, limiting their potential use in the development of pharmaceutical protocols. Herein, we present our solutions to these shortcomings, which involve a three-prong approach in the development of novel protocols, understanding the underlying mechanisms through detailed kinetic analysis, and by the development of new tools to facilitate mechanistic investigation for practitioners who may not possess specialized photochemical equipment. In this work, we were the first to demonstrate that radicals derived from amines, commonly employed as “sacrificial” electron-donors, can also act as reducing agents in photoredox transformations. We also present examples in which Methylene Blue, an inexpensive, non-toxic organic dye, can be employed as a viable alternative to ruthenium complexes for photoredox transformations. By employing a photosensitizer with more favourable excited state kinetics for electron-transfer, we successfully demonstrated that Methylene Blue could be used to increase the efficiency of a previously developed photoredox transformation. While employing organic dyes is an excellent strategy to lowering the cost of photoredox transformations, another viable strategy is to employ heterogeneous semiconductors. Titanium dioxide is an example of a semiconductor which is often employed in photocatalytic applications due to its low cost, desirable redox properties, and high chemical stability which allows for continued use. However, titanium dioxide has seen limited use in organic synthesis due to the requirement of UV irradiation for excitation. Herein, we present a process which led to the discovery of visible light photochemistry with titanium dioxide, generated through the adsorption of indole substrates creating a new, visible light absorbing complex. Employing this strategy, we were able to promote the photocatalytic Diels–Alder reaction of indoles with electron-rich dienes, giving access to valuable tetrahydrocarbazole scaffolds. Finally, in order to facilitate the characterization of chain processes in photoredox catalysis, we have successfully developed a visible light actinometer based on the ubiquitous photocatalyst, Ru(bpy)3Cl2. This actinometer offers many advantages compared to other visible light actinometers, such as completely eliminating the need for spectral matching, as the actinometer is also the photocatalyst. This technique should provide researchers with a mechanistic tool to properly characterize chain propagation in the transformation of interest.

No description available.

No description available.

Over the past twenty years molecules capable of templating their own synthesis, so called self–replicating molecules have gained prominence in the literature. We show herein that mixing the reagents for replicating molecules can produce a network of self–replicators which coexist and that the networks can be instructed by the addition of preformed template upon initiation of the reaction. Whilst self–replicating molecules offer the simplest form of replication, nature has evolved to utilise not minimal self–replication but reciprocal replication where one strand templates the formation of not an identical copy of itself but a reciprocal strand. Efforts thus far at producing a synthetic reciprocal replicating system are discussed and an alternative strategy to address the problems encountered is proposed and successfully implemented. The kinetic behaviour of a self–replicating reaction bears two distinctive time periods. Upon initiation, the reaction proceeds slowly as no template exists to catalyse the reaction. Upon production of the template, the reaction proceeds more rapidly via template direction. During this slow reaction period, the system is prone to mistakes as the reaction is slow and unselective. The creation of an [A•B] binary complex through non–covalent recognition of reagents allows for the reaction to proceed at an accelerated rate upon initiation however products of such a reaction are usually catalytically inert and do not promote further template directed reaction. A strategy to combine the desired behaviour of an [A•B] binary complex with the further template directed autocatalytic self–replicating reaction is described and implemented. Supramolecular polymers consist of repeating monomers which are held together by non–covalent interactions. The strong association of a self–replicating template dimer is comparable to that of supramolecular polymers reported thus far in the literature which are produced by cumbersome standard linear synthetic procedures. Herein the application of self–replication to the field of supramolecular polymer synthesis is discussed. As the autocatalytic reaction to produce the template monomers occurs under the same conditions as required to allow polymerisation to proceed, the polymer is able to spontaneously form in situ by self–replicating supramolecular polymerisation.

A presente dissertação tem por objetivo o estudo dos rearranjos de Pummerer, ainda não descritos na literatura para α-alquiltio-sulfóxidos. É apresentado um apanhado bibliográfico que consta de duas partes: a) Um relato dos trabalhos sobre os rearranjos de Pummerer com os sulfóxidos que não possuem átomo de enxofre na cadeia carbônica. b) Um resumo dos trabalhos que estudam algumas reações de α-alquiltio-sulfóxidos. Na primeira parte desta revisão é dado destaque às possibilidades mecanísticas da reação de Pummerer, apontando-se a sua dependência dos diversos fatores, tais como as estruturas do sulfóxido, do reagente de Pummerer e das condições experimentais empregadas. Na segunda parte são destacadas a acidez aumentada do grupo metilena de α-alquiltio-sulfóxidos e a sua fácil hidrólise ácida, características estas de grande importância para o nosso estudo da reação de Pummerer com os referidos compostos. No presente trabalho são preparados quatro sulfóxidos: metil n-propilsulfóxido (I) metil metiltiometilsulfóxido (II) etil etiltiometilsulfóxido (III) e fenil feniltiometilsulfóxido (IV), todos eles já descritos na literatura. São descritas as reações do etil etiltiometilsulfóxido (III) com anidrido acético. O rearranjo de Pummerer não ocorre em condições brandas, havendo recuperação do sulfóxido de partida. Em condições mais enérgicas e isolado o ortotritioformiato de etila. É relatada a reação do mesmo sulfóxido (III) com ácido clorídrico aquoso, na qual houve recuperação de grande parte do produto de partida e formação de pequenas quantidades do dietildissulfeto. São apresentadas as reações do metil metiltiometilsulfóxido (II), etil etiltiometilsulfóxido (III) e fenil feniltiomtilsulfóxido (IV) com cloreto de tionila. Em todas elas, em vez do cloro ditioacetal esperado, produto normal do rearranjo de Pummerer ocorre formação de clorometil-sulfetos correspondentes em rendimentos de 70-90%, ao lado de dissulfetos correspondentes. Finalmente é relatada a reação do etil etiltiometilsulfóxido (III) com cloreto de benzoila. Nesta reação há também ausência do produto normal do rearranjo de Pummerer e formação de dois produtos principais: clorometilsulfeto e tioformiato de etila, ao lado de pequenas quantidades de dissulfeto e ácido benzoico. Na discussão dos resultados obtidos são destacados dois aspectos de maior-importância nas reações dos α-alquil-tio-sulfóxidos: a supressão do produto de rearranjo de Pummerer e a formação de clorometil-sulfetos nas reações com cloreto de tionila e cloreto de benzoila. São relatadas as medidas de basicidades relativas pelo emprego de dois doadores de prótons, pirrol e fenol, através do método de espectroscopia no infra-vermelho do etil etiltiometilsulfóxido (II) e metil metiltiometilsulfóxido (II) em comparação com os sulfóxidos correspondentes não substituidos. Os dados obtidos voNH e voOH indicam uma diminuição de basicidade do oxigênio sulfinílico, resultante da introdução de um átomo de enxofre na posição 2 dos sulfóxidos. É sugerida a diminuição de basicidade e em consequência da nucleofilicidade do oxigênio sulfinílico como responsável pela diminuição da reatividade com os reagentes de Pummerer. É proposto o mecanismo de três passos para a formação de clorometil-sulfetos nas reações com cloreto de tionila e cloreto de benzoila. A formação de ortotritioformiato de etila e tioformiato de etila nas reações com anidrido acético e cloreto de benzoila, respectivamente é interpretada como decorrente do rearranjo de Pummerer. / This thesis investigates the Pummerer rearrangements not described in the literature, for some α-alkylthio-sulphoxides. A literature report divided in two parts is presented: a) Pummerer rearrangements of the sulphoxides not containing sulphur atom in the carbon chain. b) Some investigations on the reactions of α-alkylthio-sulphoxides. In the first part, the mechanistic aspects of the Pummerer rearrangement are described being emphasized their dependence on several factors, such as the structure of the sulphoxide and Pummerer reagent, and experimental conditions. In the second part the increased acidity of the methylene group of the α-alkylthio-sulphoxides and its easy hydrolysis are appointed, as they are of great importance for our study of the Pummerer rearrangement. In the present work: 1. Four sulphoxides already described in the literature are prepared: methyl methylthiomethylsulphoxide (I), methyl n-propylsulphoxide (II), ethyl ethylthiomethylsulphoxide (IV), and phenyl phenylthiomethylsulphoxide (IV). 2. The reactions of ethyl ethylthiomethylsulphoxide (III) with acetic anhydride are described. The Pummerer rearrangement does not occur in mild conditions being recovered the starting material. In more drastic condition the ethyl trithioformate is isolated. 3. The reaction of the same sulphoxide (III) with hydrochloric diluted acid is reported to give mostly starting material and small amount of diethyldisulphide. 4. The reactions of methyl methylthiomethylsulphoxide (I), ethyl ethylthiomethylsulphoxide (III) and phenyl phenylthiomethylsulphoxide (IV) with thionyl chloride are presented. In all cases instead of the expected chloro dithioacetal, the normal Pummerer rearrangement product, chloromethylsulphides were identified in the 70-90% yield in mixture with small amounts of the corresponding disulphides. 5. The reaction of ethyl ethylthiomethylsulphoxide (III) with benzoyl chloride is reported. Again the absence of the normalPummerer rearrangement product with formation of chloromethyl sulphoxide and small amount of disulphide are observed. However, an addicional product, ethylthioformate, was also produced. 6. The suppression of the normal Pummerer rearrangement product and formation of chloromethyl-sulphides in the reaction with thionyl chloride and benzoyl chloride are discussed. The relative basicity measurements using pirrol and phenol as proton donors by IR spectroscopy are reported for ethyl ethylthiomethylsulphoxide (III) and methyl methylthiomethylsulphoxide (I) and compared to the corresponding unsubstituted sulphoxides. The obtained data (voNH and voOH) indicate a decrease of basicity of sulphinyl group by replacement of β-methylene group by sulphur atom in the sulphoxides studied. Is suggested that decrease in basicity and consequently of nucleophilicity of the oxygen atom is responsible for the decrease of reactivity toward Pummerer reagents. A three step mechanism is proposed for the formation of chloromethyl-sulphides in the reactions with thionyl chloride and benzoyl chloride. The formation of ethyl orthotriethyl thioformate and ethyl thioformate as secondary products in the reactions with acetic anhydride and benzoyl chloride respectively is interpreted as resulting from the Pummerer rearrangement.