Photoactive EDA complexes in visible light driven aerobic oxidations

Organic synthesis driven by photochemical activation has been proven very promising in a range of scenarios within academia and industry. The emergence of photoredox catalysis has fueled an ever-growing interest in the use of visible light as a convenient energy source for a variety of radical reactions otherwise difficult to achieve. However, the use of homogeneous catalysts, based on transition metals or complicated organic dyes as the light harvesting moiety, does not come without drawbacks. Problems include the price and availability of ruthenium and iridium, and the separation and re-use of the catalysts from the products. Photochemical transformations that use simpler systems, such as catalyst-free versions or small organic molecules as photocatalysts, are therefore attractive to develop. For certain systems, one potential solution to these problems is the use of electron donor-acceptor (EDA) complexes. These complexes can form between a molecule of high electron affinity (acceptor) and a molecule of low ionization potential (donor). A key feature of the EDA complex is that it can be excited with light of a lower energy than that needed to excite the reactants on their own. The excitation of the complex can result in the formation of reactive radical species that can be harvested for further chemical reactions. EDA complexes can, with other words, be used as a convenient light-absorbing moiety to drive chemical reactions without the need of an external photocatalyst.\ua0Oxidation reactions are a universal part of organic chemistry. The oxidants commonly used are however associated with certain drawbacks such as troublesome waste production. Oxygen obtained from the air around us is a potentially ideal alternative. The use of aerobic conditions in the combination with photoactive EDA complexes poses an interesting and underdeveloped part of photochemical transformations. In this thesis, an EDA complex approach to the synthesis of N-heterocycles has been investigated. The developed methods use alkylated anilines as donors and activated alkenes as acceptors to form different EDA complexes. Visible light is used to activate the complexes, and aerobic oxygen is used as the terminal oxidant to furnish the target compounds. In the first part of the thesis, new EDA complexes between dialkyl anilines and 1,2-dibenzoyl ethylenes are identified. The results show that upon excitation of the EDA complexes, 3,4-disubstituted tetrahydroquinolines can be formed in excellent diastereoselectivity and in high yields. In the second part, the identified EDA complexes are used as part of a catalytic system for the generation of α-amino alkyl radicals under aerobic conditions and under visible light irradiation. Lastly, in the third part, new EDA complexes between arylated amino acids and maleimides are identified. The photoactivation of these complexes was shown to be an efficient way of generating secondary α-amino alkyl radicals to furnish N-H-tetrahydroquinolines

Overcoming Back Electron Transfer in the Electron Donor-Acceptor Complex-Mediated Visible Light-Driven Generation of α-Aminoalkyl Radicals from Secondary Anilines

An additive-free, visible light-driven annulation between N-aryl amino acids and maleimide to form tetrahydroquinolines (THQs) is disclosed. Photochemical activation of an electron donor-acceptor (EDA) complex between amino acids and maleimides drives the reaction, and aerobic oxygen acts as the terminal oxidant in the net oxidative process. A range of N-aryl amino acids and maleimides have been investigated as substrates to furnish the target THQ in good to excellent yield. Mechanistic investigations, including titration and UV-vis studies, demonstrate the key role of the EDA complex as the photoactive species

Aerobic Oxidative EDA Catalysis: Synthesis of Tetrahydroquinolines Using an Organocatalytic EDA Active Acceptor

A catalytic electron donor-acceptor (EDA) complex for the visible-light-driven annulation reaction between activated alkenes and N,N-substituted dialkyl anilines is reported. The key photoactive complex is formed in situ between dialkylated anilines as donors and 1,2-dibenzoylethylene as a catalytic acceptor. The catalytic acceptor is regenerated by aerobic oxidation. Investigations into the mechanism are provided, revealing a rare example of a catalytic acceptor in photoactive EDA complexes that can give access to selective functionalization of aromatic amines under mild photochemical conditions

Visible-Light-Driven Stereoselective Annulation of Alkyl Anilines and Dibenzoylethylenes via Electron Donor-Acceptor Complexes

A catalyst-free, stereoselective visible-light-driven annulation reaction between alkenes and N,N-substituted dialkyl anilines for the synthesis of substituted tetrahydroquinolines is presented. The reaction is driven by the photoexcitation of an electron donor-acceptor (EDA) complex, and the resulting products are obtained in good to high yields with complete diastereoselectivity. Mechanistic rationale and photochemical characterization of the EDA-complex are provided

Rare Events in Remote Dark-Field Spectroscopy: An Ecological Case Study of Insects

In this paper, a novel detection scheme for the monitoring of insect ecosystems is presented. Our method is based on the remote acquisition of passive sunlight scattering by two insect species. Procedures to identify rare events in remote dark-field spectroscopy are explained. We further demonstrate how to reduce the spectral representation, and how to discriminate between sexes, using a hierarchical clustering analysis. One-day cycle showing the temporal activities of the two sexes as well as data on activity patterns in relation to temperature and wind is presented. We also give a few examples of the potential use of the technique for studying interactions between sexes on a time scale of milliseconds

Island biology and morphological divergence of the Skyros wall lizard Podarcis gaigeae: a combined role for local selection and genetic drift on color morph frequency divergence?

<p>Abstract</p> <p>Background</p> <p>Patterns of spatial variation in discrete phenotypic traits can be used to draw inferences about the adaptive significance of traits and evolutionary processes, especially when compared to patterns of neutral genetic variation. Population divergence in adaptive traits such as color morphs can be influenced by both local ecology and stochastic factors such as genetic drift or founder events. Here, we use quantitative color measurements of males and females of Skyros wall lizard, <it>Podarcis gaigeae</it>, to demonstrate that this species is polymorphic with respect to throat color, and the morphs form discrete phenotypic clusters with limited overlap between categories. We use divergence in throat color morph frequencies and compare that to neutral genetic variation to infer the evolutionary processes acting on islet- and mainland populations.</p> <p>Results</p> <p>Geographically close islet- and mainland populations of the Skyros wall lizard exhibit strong divergence in throat color morph frequencies. Population variation in throat color morph frequencies between islets was higher than that between mainland populations, and the effective population sizes on the islets were small (N_e:s < 100). Population divergence (F_ST) for throat color morph frequencies fell within the neutral F_ST-distribution estimated from microsatellite markers, and genetic drift could thus not be rejected as an explanation for the pattern. Moreover, for both comparisons among mainland-mainland population pairs and between mainland-islet population pairs, morph frequency divergence was significantly correlated with neutral divergence, further pointing to some role for genetic drift in divergence also at the phenotypic level of throat color morphs.</p> <p>Conclusions</p> <p>Genetic drift could not be rejected as an explanation for the pattern of population divergence in morph frequencies. In spite of an expected stabilising selection, throat color frequencies diverged in the islet populations. These results suggest that there is an interaction between selection and genetic drift causing divergence even at a phenotypic level in these small, subdivided populations.</p

Polycyclizations of Ketoesters: Synthesis of Complex Tricycles with up to Five Stereogenic Centers from Available Starting Materials

Here we present a polycyclization of oxotriphenylhexanoates. The polycyclization is governed by electronic effects, and three major synthetic paths have been established leading to stereochemically complex tricyclic frameworks with up to five stereogenic centers. The method is compatible with an array of functional groups, allowing pharmacophoric elements to be introduced post cyclization

Selection in parental species predicts hybrid evolution

AbstractWhile hybridization is recognized as important in evolution, its contribution to adaptation and diversification remains poorly understood. Using genomically diverged island populations of the homoploid hybrid Italian sparrow, we test predictions for phenotypic trait values and evolvability based on patterns of parental species divergence in four plumage color traits. We find associations between parental divergence and trait evolution in Italian sparrows. Fixed major QTL in species differences lead to hybrids with higher trait variation, and hence evolvability, than the parent species. Back and crown plumage show no correlation between current within-parent variability and among-parent differentiation. For these traits, Italian sparrow phenotypes are biased towards axes of high parental differentiation and show greater phenotypic novelty along axes of low current parental evolvability, as predicted when major QTL are involved in species differences. Crown color has consistently evolved back towards one parent, while back color varies among islands. We also find significant among-population diversification within the Italian sparrow. Hence, hybridization of the same parent species can generate different phenotypes. In conclusion, we find support for parental phenotypic divergence patterns reflecting divergence mechanisms, and hence such patterns can be useful in predicting how hybridization alters the potential to evolve and adapt.</jats:p

Remote nocturnal bird classification by spectroscopy in extended wavelength ranges

We present optical methods at a wide range of wavelengths for remote classification of birds. The proposed methods include eye-safe fluorescence and depolarization lidar techniques, passive scattering spectroscopy, and infrared (IR) spectroscopy. In this paper we refine our previously presented method of remotely classifying birds with the help of laser-induced beta-keratin fluorescence. Phenomena of excitation quenching are studied in the laboratory and are theoretically discussed in detail. It is shown how the ordered microstructures in bird feathers induce structural "colors" in the IR region with wavelengths of around 3-6 mu m. We show that transmittance in this region depends on the angle of incidence of the transmitted light in a species-specific way and that the transmittance exhibits a close correlation to the spatial periodicity in the arrangement of the feather barbules. We present a method by which the microstructure of feathers can be monitored in a remote fashion by utilization of thermal radiation and the wing beating of the bird. (C) 2011 Optical Society of Americ

Photochemical Access to Substituted β-Lactams and β-Lactones via the Zimmerman-O\u27Connell-Griffin Rearrangement

A photomediated protocol giving facile access to substituted β-lactam and β-lactones is presented. The method realizes, for the first time, the use of the Zimmerman-O\u27Connell-Griffin (ZOG) rearrangement in [2 + 2] cycloaddition. Products are obtained in high yield with excellent diastereoselectivity under visible light irradiation and under mild reaction conditions