Synthesis of a new class of homochiral amines and novel bio-active tropanes

This thesis describes two main programmes: the synthesis of a new class of homochiral amines and the synthesis of ketone analogues of 3a-esterified tropane alkaloids. In chapter one, a scaled-up synthesis of (5)-a-(diphenylmethyl)pyrrolidine 1 is described. The key hydrogenation step of the oxazolidinone intermediate 2 was extended to the synthesis of the other chiral amines 70, 73, 76, 79 and 82. Hydrogenation of the oxazolidinones proceeded in good yields (71 - 87 %) and was not susceptible to racemisation. Thus, a convenient route from amino acid ester hydrochlorides (S)-valine 65, (S)-phenylalanine 66, (S)-alanine 67, (S)-isoleucine 68 and (S)-leucine 69 allowed a range of novel chiral amines to be prepared. In chapters two and three, a new route to ketone analogues of tropane esters is described. In chapter two, results of an attempt to prepare ketone 110 are outlined. Ketone 110 is an analogue of the tropane alkaloid littorine 101, where the bridging ester O atom is replaced by a CH2 group. The first approach to ketone 110 involved the Wittig reaction of acetylmethylenephosphorane 118 and the Homer-Wadsworth- Emmons reaction of diethylbenzoylmethanephosphonate 122 with tropinone 116. Tropinone 116 was found to be particularly unreactive in both cases. The second approach to ketone 110 involved the coupling reactions of both N-troc-3a- tosyloxymethyltropane 170 and N-troc-3 a-iodomethyltropane 185 with 2-phenylacetyl- 1,3-dithiane 147 and 1,3-ditihiane 142. These were also unreactive and as a result the synthesis of ketone 110 remains unresolved. In chapter three, the synthesis of other ketone analogues of naturally occurring 3 a- esterified tropane alkaloids is described. A six-step route to the ketones was devised and in this route the Grignard reactions of tropan-3 -ylacetaldehyde 227 emerged as the key to the success of the strategy. Three ketone analogues 218, 219 and 220 of tropate esters were successfully prepared. Ketone 220, the analogue of apoatropine 201, was found to be a muscarinic acetylcholine receptor antagonist (EC(_50) 1.9x10(^-7) M) in guinea-pigileum, showing a 500-fold less activity than atropine 202. However the activity is still within the clinical range

Some applications and chemistry of (S)-2-(diphenylmethyl)-pyrrolidine

The synthetic utility of (S)-2-(diphenylmethyl)-pyrrolidine (1) and its amide derivative, (S)-2-(diphenylmethyl)-5-oxo-pyrrolidine (2) were examined in two contexts; as chiral auxiliary compounds in asymmetric alkylation reactions and Diels- Alder reactions; as chiral solvating agents (CSAs) for (^1)NMR evaluation of chiral acids and alcohols. In the former case, it was shown that monoalkylation of N-acyl derivatives of (1) and (2) using lithiated bases led to poor diastereoselectivities (1:1 to 1.12:1) and poor yields (28 to 33 %), while alkylation reactions using HMPA proceeded with modest diastereoselectivities (1.49:1 to 4.25:1). The results of the Diels-Alder study remain premature at present. In the latter case, (1) was an excellent chiral solvating agent (CSA) for chiral carboxylic acids, however it was less effective for chiral alcohols. The amide derivative (2) was substantially less effective as a CSA for chiral carboxylic acids and failed completely to resolve chiral alcohols

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

Two novel carbazole-based compounds 7a and 7b were synthesised as potential candidates for application in organic electronics. The materials were fully characterised by NMR spectroscopy, mass spectrometry, FTIR, thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, and absorption and emission spectroscopy. Compounds 7a and 7b, both of which were amorphous solids, were stable up to 291 °C and 307 °C, respectively. Compounds 7a and 7b show three distinctive absorption bands: high and mid energy bands due to locally excited (LE) transitions and low energy bands due to intramolecular charge transfer (ICT) transitions. In dichloromethane solutions compounds 7a and 7b gave emission maxima at 561 nm and 482 nm with quantum efficiencies of 5.4% and 97.4% ± 10%, respectively. At positive potential, compounds 7a and 7b gave two different oxidation peaks, respectively: quasi-reversible at 0.55 V and 0.71 V, and reversible at 0.84 V and 0.99 V. At negative potentials, compounds 7a and 7b only exhibited an irreversible reduction peak at −1.86 V and −1.93 V, respectively

Dye-sensitized solar cells: Investigation of D-A-π-A organic sensitizers based on [1,2,5]selenadiazolo[3,4-c]pyridine

The authors gratefully acknowledge financial support from the Russian Science Foundation (grant no. 15-13-10022). Wenjun Wu thanks the Scientific Committee of Shanghai (14ZR1409700) for financial support. The authors thank the Leverhulme Trust for an International Network grant.We report two series of D-A-π-A metal-free organic sensitizers for dye-sensitized solar cells (DSSCs) based on triphenylamine and N-hexyl-carbazole as electronic donors, respectively. Through varying auxiliary acceptors and π-spacers, several significant consequences on cell efficiency were identified: (i) a broadened UV-Vis absorption spectrum and low-lying LUMO level with [1,2,5]selenadiazolo [3,4-c] pyridine as auxiliary acceptor; (ii) compensation for the absorption valley around 400 nm in the UV-vis spectra by the introduction of a thiophene unit into the π-bridge; (iii) effective improvement of the power conversion efficiency (PCE) by means of cosensitization, leading to dye OKT-1 , 3.10% PCE, increased to 4.19% with squaraine dye SQ2 as co-sensitizer. The design criteria identified have opened the door for further optimization of this new dye family.PostprintPeer reviewe

Towards sustainable, solution-processed organic field-effect transistors using cashew gum as the gate dielectric

To realize low-cost, environmentally friendly electronic devices and circuits, there is currently a strong trend to explore plant-based dielectric materials because they can be responsibly sourced from agricultural or forest vegetation, are generally water-soluble, and possess good electrical insulator properties. In this contribution, organic field-effect transistors (OFETs) using a biopolymer dielectric obtained from exudates of Anacardium occidentale Linn. trees, namely, cashew gum (CG), are reported. To characterise the physical and dielectric properties of the gum, thin films and metal-insulator-metal (MIM) capacitors were prepared and characterized. To evaluate the material’s performance in OFETs, bottom-gate top-contact (BGTC) p-channel poly [3,6-di(2-thien-5-yl)-2,5-di(2-octyldodecyl)-pyrrolo (3,4-c)pyrrole-1,4-dione) thieno (3,2-b) thiophene]:polymethyl methacrylate (DPPTTT:PMMA) transistors were engineered and studied. The fabricated MIM capacitors display a comparatively high areal capacitance of 260 nF/cm2 at 1 kHz for 130 nm thick films. As a result, the solution-processed DPPTTT:PMMA OFETs favourably operate at 3 V with the average saturation field-effect mobility equal to 0.20 cm2/Vs., threshold voltage around −1.4 V, subthreshold swing in the region of 250 mV/dec, and ON/OFF current ratio well above 103. As such, cashew gum emerges as a promising dielectric for sustainable manufacturing of solution-processed organic FETs

A Review on Solution-Processed Organic Phototransistors and Their Recent Developments

Today, more disciplines are intercepting each other, giving rise to “cross-disciplinary” research. Technological advancements in material science and device structure and production have paved the way towards development of new classes of multi-purpose sensory devices. Organic phototransistors (OPTs) are photo-activated sensors based on organic field-effect transistors that convert incident light signals into electrical signals. The organic semiconductor (OSC) layer and three-electrode structure of an OPT offer great advantages for light detection compared to conventional photodetectors and photodiodes, due to their signal amplification and noise reduction characteristics. Solution processing of the active layer enables mass production of OPT devices at significantly reduced cost. The chemical structure of OSCs can be modified accordingly to fulfil detection at various wavelengths for different purposes. Organic phototransistors have attracted substantial interest in a variety of fields, namely biomedical, medical diagnostics, healthcare, energy, security, and environmental monitoring. Lightweight and mechanically flexible and wearable OPTs are suitable alternatives not only at clinical levels but also for point-of-care and home-assisted usage. In this review, we aim to explain different types, working mechanism and figures of merit of organic phototransistors and highlight the recent advances from the literature on development and implementation of OPTs for a broad range of research and real-life applications