No description available.

No description available.

No description available.

<p> One process that has the potential of efficiently harvesting solar energy is singlet fission (SF), a process by which one photon of light can produce two excited states. Investigations of three different series of bistetracene (BT) were used to explore the effect of symmetry on the rate and driving force of SF, as well as the electronic coupling. A dimer and the corresponding monomer were used to build a synthetic infrastructure and explore preliminary photophysics. All of the dimers were connected by one to three norbornyl bridges and exhibit various amounts of electronic coupling.</p><p> The first section of this dissertation will discuss a series of cofacial BT dimers with C_2v symmetry that have one (BT1) to three (BT3) norbornyl bridges linking the two tetracene chromophores. Density functional theory calculations of BT1-BT3 were used to explore the SF driving force and the change in through-space versus through-bond contributions to the electronic coupling. The C_2v symmetry was found to be unprofitable to SF, but vibrations accessible to the ground state would break the C_2v symmetry. The thorough synthetic investigation of the monomeric tetracene-norbornyl bridge was developed to build a synthetic library that aided the synthesis of BT1, the first rigid SF dimer. Preliminary photophysics of BT1 and its monomer will also be described.</p><p> In the second portion of this work, the SF driving force, electronic coupling will be calculated for the second and third series of BT dimers, which are symmetry adaptations of BT1-BT3. In the second series, the orbital overlap of the norbornyl bridge and tetracene arms will be exploited by changing how the bridge and arms are connected to make dimers of C₂ and C_s symmetry. In the final series, a heteroatom substitution of BT1 creates a series of C₂ and C_s dimers that can be built using the synthetic infrastructure developed above. Both symmetry adapted series of BT dimers were found to lead to an increase in electronic coupling, which is expected to be productive for SF.</p>

This Thesis details the development of a series of rhodium catalysed asymmetric additions to activated aldimines to give enantioenriched protected secondary amines. A particular focus has been the choice of activating group to allow deprotection of the protected amines under mild conditions, which would tolerate a wide substrate scope. Initially methyl addition to give enantioenriched arylethanamines was studied, using diphenylphosphinoyl imines, dimethylzinc as the methyl source with rhodium catalysis in the presence of a bidentate phosphine ligand. Reduction of the starting material was identified as side reaction with a Meerwein˗Verley˗Ponndorf type mechanism for the reduction being proposed. Addition of the imine to the reaction mixture via a syringe pump was found to minimise this by-product. The imine scope was tested with yields ranging from 34-73% and enantiomeric excesses from 75-93%. Subsequently, aryl additions were concentrated on using aryl boroxines and boronic acids to give enantioenriched diarylmethylamine products. Bis˗sulfamyl aldimines were identified as an overlooked substrate class for asymmetric aryl additions, which gave addition products that could be converted to free amines using mild basic aqueous conditions. The rhodium catalysed aryl boroxine addition using a chiral diene ligand was optimised after which a study into the reaction’s scope was carried out. Yields ranged from 37˗76% with diastereomeric ratios of 91:9˗>99:1 and enantiomeric excesses of 90˗>99%. Unfortunately, the unwanted meso-diastereoisomer could not be removed, leading to a lowering of enantiomeric excess after deprotection, nevertheless the free diarylmethylamine were isolated in yields of 31-99% and enantiomeric excesses of 82-97%. Leading on from this work, a novel class of N-sulfamyl aldimines were developed which could be deprotected under the same mild conditions, and would avoid the problem of the undesired meso-diastereoisomer. A scalable synthesis of these substrates was developed. However, aryl addition proved more problematic with imine hydrolysis being a major side reaction. Eventually a set of conditions were settled on and the scope investigated briefly. The yields were found to depend on the electronic character of the substrates and the ligand employed. Finally, a brief investigation into the iridium catalysed reductive coupling of these activated aldimines and alkynes to give allylic amines was carried out. However, useful conversions were not achieved, with imine and alkyne hydrogenation being competing reactions.

No description available.

No description available.

No description available.

No description available.

The cycloaddition of benzonitrile oxide to 2-alkoxy-5,6- dihyclro-2H-pyrans was investigated with particular interest in the factors affecting the regio- and stereoselectivity of the reaction. The 2-methoxy analogue showed weak activity and little selectivity. The isolated products consisted of two by-products, three 1:1 cycloadducts and three 2:1 cycloadducts. The -butoxy analogue afforded only two cycloadducts. Both arose from attack anti to the bulky alkoxy substituent. Addition of benzonitrile oxide and Q,j-dipheny1njtrone to a bridged pyran, 6,8-dioxabicyclo[3 .2. l]oct-3-ene, showed similar selectivity and much enhanced reactivity. Levoglucosenone, a chiral bicyclic enone showed excellent reactivity and selectivity in reaction with benzonitrile oxide. Two cycloadducts were isolated in a ratio of ca. 100:1 and a combined yield of 71%; the major adduct having added from the face anti to the methyleneoxy bridge. This isoxazoline was investigated further in reactions involving reduction of the carbonyl group, acetal formation and nucleophilic addition of nitromethane. Levoglucosenone was also shown to be a reactive dipolarophjle to other 1,3-dipoles such as nitrones, a nitrile imine and a carbohydrate nitrile oxide. The chemistry of some of these adducts was also investigated. Finally, the Michael addition of nitromethane to levoglucosenone was investigated under many different conditions and with different basic catalysts. The aim was to synthesise levoglucosenone with a primary nitro substituent to use as a nitrile oxide precursor. The series of reactions afforded 8 identifiable products, none of which was the desired Michael adduct.