22 research outputs found
Enantioselective palladium and isothiourea dual catalysis
No full textThis thesis details the development of dual catalytic processes involving achiral palladium and enantiopure isothiourea catalysts for the synthesis of enantioenriched and highly functionalised products. Taking inspiration from related literature examples demonstrating the compatibility of palladium and isothiourea catalysis, the extension of existing methodologies as well as the development of novel processes were investigated.
Based on the relay catalytic allylic amination/[2,3]-rearrangement protocol, previously developed in our group for the synthesis of enantioenriched α-amino ester derivatives, the scope and limitations of this process were probed. Initial studies aimed at identifying functional groups that could be tolerated in the relay catalysis. Electron-withdrawing amide substituents proved most promising and were explored in more depth to furnish enantioenriched α-amino ester derivatives featuring a 1,4-dicarbonyl motif.
As processes reported so far had focused on ammonium enolates as reaction partners, the range of reactivity modes accessible by isothiourea catalysis had not been fully exploited in dual catalytic methodologies. As such, the development of a cooperative palladium and isothiourea catalysis process employing α,β-unsaturated acyl ammonium intermediates was explored. This process furnishes enantioenriched cyclopentane products with up to four contiguous stereogenic centres with high stereoselectivity (up to 99:1 dr, up to 97:3 er). The scope and limitations of this process were probed, with subsequent derivatisation reactions demonstrating the synthetic utility of the products. In addition, a range of control experiments provided insight into the mechanism of this cooperative palladium and isothiourea catalysis
Ligandendesign für die asymmetrische Transferhydrierung in Wasser
No full textThe present thesis focuses on the synthesis of new chiral ionic ligands designed to fulfill the requirements for the application in asymmetric transfer hydrogenations. Based on a chiral amino alcohol and a chiral diamine structural motive, highly coordinating chiral ionic ligands with bidentate structural motive were obtained. By introducing an ionic head group, the solubility of the designed ligands could be adapted via the choice of anion. Moreover, different substitution patterns for diamine based chiral ionic ligands were exploited. The newly designed ligands were successfully applied in transition metal catalyzed asymmetric transfer hydrogenation in aqueous medium. By taking advantage of the tunable properties of the designed ligands, their positive effect on asymmetric transfer hydrogenation could be demonstrated
α,β-Unsaturated acyl ammonium species as reactive intermediates in organocatalysis : an update
No full textAuthors acknowledge The University of St Andrews (JB) and the EaSICAT Centre for Doctoral Training (MTW) for funding.α,β-Unsaturated acyl ammonium species are versatile intermediates that have been applied in a variety of transformations including Michael additions, domino reactions and cycloadditions. Many of these transformations are promoted by chiral Lewis base catalysts, enabling the rapid generation of molecular complexity with high stereochemical control. This review highlights recent developments in the generation and application of α,β-unsaturated acyl ammonium intermediates reported since a previous review of this area in 2016. Particular emphasis will be placed on reports providing mechanistic insight into catalytic transformations and observed selectivities. A perspective on current challenges and potential future developments in the field of α,β-unsaturated acyl ammonium catalysis is also provided.Peer reviewe
Synthesis of Benzothiophene and Benzoselenophene Fused Compounds and Their Application as OFET Materials
No full text
Coordinating chiral ionic liquids for asymmetric transfer hydrogenation reactions in water
No full textExploring the scope of tandem palladium and isothiourea relay catalysis for the synthesis of α-amino acid derivatives
No full textFunding: This research was funded by the School of Chemistry, University of St Andrews. A.D.S. thanks the Royal Society for a Wolfson Research Merit Award.The scope and limitations of a tandem N-allylation/[2,3]-rearrangementprotocol are investigated through the incorporation of a variety of functionalgroups within an allylic phosphate precursor. This method uses readilyaccessible N,N-dimethylglycine aryl esters and functionalizedallylic phosphates, forming quaternary ammonium salts in situ in the presence of a palladium catalyst. Subsequentenantioselective [2,3]-sigmatropic rearrangement, promoted by the chiralisothiourea tetramisole, generates α-amino acid derivatives with two contiguousstereocenters. The incorporation of electron withdrawing ester and amide groupsgave the best results, furnishing the desired products in moderate to goodyields (29-70%), with low diastereocontrol (typically 60:40 dr) but highenantioselectivity (up to 90:10 er). These results indicate that substrate-catalystinteractions in the proposed transition state are sensitive to the substitutionpattern of the substrates.Peer reviewe
Cooperative palladium/isothiourea catalyzed enantioselective formal (3+2) cycloaddition of vinylcyclopropanes and α,β-unsaturated esters
No full textThe research leading to these results has received funding from the University of St Andrews (JB) and the EaSI-CAT centre for Doctoral Training (AJN).A protocol for the enantioselective synthesis of substituted vinylcyclopentanes has been realised using cooperative palladium and isothiourea catalysis. Treatment of vinylcyclopropanes with Pd(PPh3)4 generates a zwitterionic π-allyl palladium intermediate that intercepts a catalytically generated α,β-unsaturated acyl ammonium species prepared from the corresponding α,β-unsaturated para-nitrophenyl ester and the isothiourea (R)-BTM. Intermolecular formal (3+2) cycloaddition between these reactive intermediates generates functionalised cyclopentanes in generally good yields and excellent diastereo- and enantiocontrol (up to >95 : 5 dr, 97 : 3 er), with the use of LiCl as an additive proving essential for optimal stereocontrol. To the best of our knowledge a dual transition metal/organocatalytic process involving α,β-unsaturated acyl ammonium intermediates has not been demonstrated previously.Peer reviewe
Asymmetric Transfer Hydrogenation in Thermomorphic Microemulsions Based on Ionic Liquids
No full textIon-Tagged Chiral Ligands for Asymmetric Transfer Hydrogenations in Aqueous Medium
No full textWe report the design and synthesis of novel ion-tagged chiral ligands for asymmetric transfer hydrogenation (ATH) in aqueous medium. Based on (R,R)-1,2-diphenylethylene diamine (DPEN) as structural motif, a straightforward three-step protocol was developed that gave access to novel chiral ligands with carbamate-substructure and pyridinium headgroup. The careful optimization of steric and electronic properties in combination with the adaption of solubility via choice of the anion gave a set of chiral and water-soluble ligands for use in ruthenium-catalyzed asymmetric transfer hydrogenations in aqueous medium. Eventually, a pool of aliphatic and aromatic ketones as well as two imine substrates were reduced with excellent isolated yields up to 95% and enantioselectivities >90% ee under environmentally benign conditions in the absence of additional surfactants
