Papers by Christopher J. Richards
Organic & Biomolecular Chemistry
The synthesis of β-aryl α,β-unsaturated lactones and lactams in high enantiomeric excess is descr... more The synthesis of β-aryl α,β-unsaturated lactones and lactams in high enantiomeric excess is described, and the key copper-catalysed reduction methodology with the parent Josiphos ligand is applied to the asymmetric synthesis of lucidulactone A.
European Journal of Organic Chemistry, 2021
Starting from (R)‐Ugi's amine, diastereoselective lithiation followed by Ar'PCl2 and then... more Starting from (R)‐Ugi's amine, diastereoselective lithiation followed by Ar'PCl2 and then Ar’’MgBr led to the generation, as single diastereoisomers, of (R,Sp,Sphos) [Ar’=Ph, Ar’’=o‐Tol] and (R,Sp,Rphos) [Ar’=o‐Tol, Ar’’=Ph] PPFA ligand derivatives. Amine substitution of both with HPCy2 gave P‐stereogenic Josiphos ligands, and then addition of CuCl, the corresponding copper(I) complexes. The latter were also generated by using borane P and N protecting groups and in situ Cu(I) complexation, avoiding the isolation of air‐sensitive phosphine intermediates. This protection methodology was also applied to the synthesis of Josiphos/CuCl complexes derived from PCl3. In addition, related bulky cobalt‐sandwich complex‐based derivatives were also obtained. Preliminary investigation revealed isolated CuCl complexes as competent catalyst precursors for enantioselective conjugate addition reactions.
European Journal of Inorganic Chemistry, 2022
The palladium catalysed reaction of 1-iodo-2methylnaphthalene and 2-methyl-1-naphthylmagnesium br... more The palladium catalysed reaction of 1-iodo-2methylnaphthalene and 2-methyl-1-naphthylmagnesium bromide gave quantitatively an (Sa)-configured cross-coupled product in 80% e.e. using (R,Sp)-PPFA as a ligand. N,N-Dimethylaminomethylferrocene was cyclopalladated (Na2PdCl4, (S)-Ac-Phe-OH, 93% e.e., as determined by 1 H NMR as a result of selfinduced non-equivalence), and the resulting (Sp)-configured dimeric palladacycle was employed as a precatalyst for this cross-coupling reaction (5 mol%). Addition to the palladacycle of diphenylphosphine and subsequent base-promoted bidentate ligand synthesis and palladium capture gave an in situ generated catalyst resulting in an (Sp)-configured product in up to 71% e.e.
The Journal of Organic Chemistry, 2020
An expeditious route to planar chiral sulfur-based scaffolds has been achieved in two operational... more An expeditious route to planar chiral sulfur-based scaffolds has been achieved in two operational steps from cheap and commercial [2.2]paracyclophane hydrocarbon. The sulfur atom was introduced in a specific benzylic position of the [2.2]paracyclophane according to a reductive sulfanylation reaction, which proceeds under two complementary reaction conditions with either the BF3•OEt2/Et3SiH or TFA/BH3. THF combinations. The study was completed by the development on a highly efficient resolution approach by HPLC.
European Journal of Inorganic Chemistry, 2016
Ferrocenyl (Fc) and phenyl (Ph) containing imines FcCH=NCH(R)Ph and FcCH(R)N=CHPh (R = H and Me) ... more Ferrocenyl (Fc) and phenyl (Ph) containing imines FcCH=NCH(R)Ph and FcCH(R)N=CHPh (R = H and Me) were cycloiridated using [Cp*IrCl2]2 with NaOAc in CH2Cl2. All resulted in the formation of neutral chloride ligated half‐sandwich iridacycles as a result of ortho‐phenyl and not alpha‐ferrocenyl C–H activation. The complexes derived from FcCH=NCH(R)Ph (R = H, Me) were obtained as a mixture of E and Z imine isomers, and with R = Me the product obtained from the (S)‐imine was isolated by recrystallisation as a single diastereoisomer. The configuration was determined by an X‐ray crystal structure analysis as SC,RIr,E.
Organic & Biomolecular Chemistry
Kinetic resolutions resulting in a new stereogenic centre were used to establish that in double a... more Kinetic resolutions resulting in a new stereogenic centre were used to establish that in double asymmetric synthesis the faster reaction is more selective. The relative rate is estimated by a model using substrate (x) and catalyst (y) selectivities.
During the last years, planar chiral [2.2]paracyclophane (PCP) derivatives have attracted conside... more During the last years, planar chiral [2.2]paracyclophane (PCP) derivatives have attracted considerable interest due to their unusual structural and electronic properties and were successfully applied in a diverse array of chemical disciplines, including polymer science, advanced materials and catalysis.
Journal of the American Chemical Society, 2003
COP-Cl catalyzes the rearrangement of (E)-allylic trichloroacetimidates to provide transposed all... more COP-Cl catalyzes the rearrangement of (E)-allylic trichloroacetimidates to provide transposed allylic trichloroacetamides of high enantiopurity, a transformation that underlies the first truly practical method for transforming prochiral allylic alcohols to enantioenriched allylic amines and congeners. The high functional group compatibility of this asymmetric rearrangement and the demonstrated broad utility in synthesis of the allylic trichloroacetimidate to allylic trichloroacetamide conversion are singular features of this new catalytic asymmetric reaction.
Starting from (η-acetylcyclopentadienyl)(η-tetraphenylcyclobutadiene)cobalt(I), highly enantiosel... more Starting from (η-acetylcyclopentadienyl)(η-tetraphenylcyclobutadiene)cobalt(I), highly enantioselective (99% ee) (S)-CBS catalysed ketone reduction followed by stereospecific alcohol-azide exchange, azide reduction and dimethyllation gave (R)-(η-α-N,Ndimethylaminoethylcyclopentadienyl)(η-tetraphenylcyclobutadiene) cobalt(I) (Arthurs’ amine). This underwent highly diastereoselective cyclopalladation to give di-μ-acetate-bis-(R)-[(η-(Sp)-2-(α-N,Ndimethylaminoethyl)cyclopentadienyl, 1-C, N)(η-tetraphenylcyclobutadiene)cobalt(I)]dipalladium, and highly diastereo-selective lithiation to give (R)-(η-(Sp)-1-(α-N,N-dimethylaminoethyl)-2(diphenylphosphino)cyclopentadienyl)(η-tetraphenylcyclobutadiene)cobalt(I) (PPCA) following the addition as electrophile of chlorodiphenylphosphine. This PN-ligand was converted into (R)-(η(Sp)-1-(α-dicyclohexylphosphinoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η-tetraphenylcyclobutadiene)cobalt(I), a PP-ligand (Rossiphos), by stereospecific amine-phosphi...
Synlett
Starting from (S,S)-1,1′-bis(4-isopropyloxazolin-2-yl)ferrocene, all possible 2-trimethylsilyl- a... more Starting from (S,S)-1,1′-bis(4-isopropyloxazolin-2-yl)ferrocene, all possible 2-trimethylsilyl- and 2,2′-di(trimethylsilyl)-substituted diastereoisomers, potential bisoxazoline ligands for use in asymmetric catalysis, were synthesised by selective lithiation followed by addition of trimethylsilyl chloride. Access to the (S,S,R p,R p)-diastereoisomer was achieved following diastereoselective introduction of two deuterium-blocking groups and utilisation of the high k H/k D value for lithiation, methodology that was also applied to the synthesis of a related 2,2′-di(diphenylmethanol)bisoxazoline ligand.
Organic & Biomolecular Chemistry
The first demonstration of a chiral palladacycle precatalyst in Pd(0) mediated asymmetric synthes... more The first demonstration of a chiral palladacycle precatalyst in Pd(0) mediated asymmetric synthesis is achieved by a novel ligand synthesis/palladium capture procedure.
The Journal of Organic Chemistry
European Journal of Inorganic Chemistry
The Friedel-Crafts acetylation of pentaphenylferrocene has been revisited using 1.1 equivalents o... more The Friedel-Crafts acetylation of pentaphenylferrocene has been revisited using 1.1 equivalents of AcCl/AlCl3 in CH2Cl2 at room temperature leading to the synthesis of 1-acetyl-1',2',3',4',5'pentaphenylferrocene (78% yield). Increased quantities of reagents and longer reaction times resulted in acetylation of the phenyl groups exclusively at the para-position, this methodology culminating in the synthesis of 1-acetyl-1',2',3',4',5'-penta(paraacetylphenyl)ferrocene (32% for a two step process). Subsequent asymmetric reduction of all six ketone functionalities with BH3.SMe2 catalysed by 60 mol % (S)-CBS proceeded in 81% yield to give (R,R,R,R,R,R)-1-(α-hydroxyethyl)-1',2',3',4',5'-penta(para-(αhydroxyethyl)phenyl)ferrocene, a highly functionalised enantiopure building block for the synthesis of ligands and materials.
Proceedings of The 4th International Electronic Conference on Synthetic Organic Chemistry
Attachment of a chiral imidazole or chiral oxazoline to either (h 5-cyclopentadienyl)(h 4tetraphe... more Attachment of a chiral imidazole or chiral oxazoline to either (h 5-cyclopentadienyl)(h 4tetraphenylcyclobutadiene)cobalt or pentaphenylferrocene results in the heterocycle mimicking an environment of planar chirality. This chiral relay effect is demonstrated by both highly diastereoselective palladation and application of the oxazoline complexes as ligands in asymmetric catalysis.
Organometallics
S4 1. Experimental procedures General information Experiments are depicted in the order they are ... more S4 1. Experimental procedures General information Experiments are depicted in the order they are presented in the accompanying manuscript. Diethyl ether and THF were distilled over sodium and benzophenone ketyl. Acetonitrile and dichloromethane were dried by distillation from calcium hydride. Methanol was dried over 4 Å molecular sieves. All cycloiridation reactions and reactions involving the use of dry solvents were carried out under an inert atmosphere of either nitrogen or argon. Silica gel (60 Å pore size, 40-63 µm technical grade) and neutral aluminium oxide (Brockmann I, 50-200 µm) were used for chromatography. All starting materials not commercially available are specifically referenced. All protons and carbons were assigned using 2D NMR techniques including HSQC, HMBC, NOESY and COESY. Carbons denoted with a prime (e.g. C 2') indicate the most deshielded carbon when there are two carbons with the same number on the structure. Carbons denoted with two superscripts (e.g. C 2/3) indicate where two environments cannot be distinguished from one another. Use was made of 1 H and 13 C NMR spectroscopy to confirm compound purity in addition to identity, and copies of these spectra are included below.
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Papers by Christopher J. Richards