Planar chiral palladacycle precatalysts for asymmetric synthesis

Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of HPAr2/base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a bidentate Phosferrox/Pd(0) complex. A series of these complexes were generated in situ and applied successfully as catalysts for asymmetric allylic alkylation

Deuterium as a Stereochemically Invisible Blocking Group for Chiral Ligand Synthesis

Highly diastereoselective lithiation (s-BuLi/TMEDA ix Et2O, -78 degrees C, 2 h) of (5)-2-ferroceny1-4-(substituted)-oxazolines followed by addition of MeOH-d(4) gave up to 95% D incorporation. Subsequent application of alternative lithiation conditions (n-BuLi in THF, -78 degrees C, 2 h), followed by addition of an electrophile, resulted in a reversal of diastereoselectivity controlled primarily by the high k(H)/k(D) value for lithiation (isomer ratio typically between 10:1 and 20:1)

Application of Transmetalation to the Synthesis of Planar Chiral and Chiral-at-Metal Iridacycles

Diastereoselective lithiation of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline followed by addition of HgCl2 resulted in the formation by transmetallation of an (S,Sp)-configured mercury substituted complex. Addition to this of [Cp*IrCl2]2 and tetrabutylammonium chloride resulted in a second transmetallation reaction and formation of an (S,Sp,RIr)-configured chloride-substituted half-sandwich iridacycle as exclusively a single diastereoisomer. By reversing the lithiation diastereoselectivity by use of a deuterium blocking group an alternative (S,Rp,SIr)-configured iridacycle was synthesised similarly. Use of (R)-Ugi’s amine as substrate in the lithiation/double transmetallation sequence gave a (R,Sp,SIr)-configured half-sandwich iridacycle, complexes of this type being previously unavailable by direct cycloiridation. Lithium to gold transmetallation was also demonstrated with the synthesis of an (S,Sp)-configured Au(I) ferrocenyloxazoline derivative. Use of the (S,Rp,SIr)-iridacycle as a catalyst for the formation of a chiral product by reductive amination with azeotropic HCO2H/NEt3 resulted in a racemate

Enantiopure planar chiral and chiral-at-metal iridacycles derived from bulky cobalt sandwich complexes

Reaction of (η5-(S)-2-(4-methylethyl)oxazolinylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt with [IrCp*Cl2]2 in acetonitrile with KPF6 and KOt-Bu resulted in S,Sp,SIr and S,Rp,RIr configured acetonitrile and Cp* coordinated cationic iridacycles (d.r. up to 4.8 : 1 – kinetic control), the planar chiral configuration dictating the configuration of the pseudo-tetrahedral iridium-based stereogenic centre. Addition of water to the cycloiridation reaction resulted in an increase in yield (up to 78%) at the cost of diastereoselectivity. Use of the corresponding substrate containing a t-Bu rather than an i-Pr substituted oxazoline gave exclusively the S,Sp,SIr diastereoisomer, and under the same conditions (S)-2-ferrocenyl- 4-(1,1-dimethylethyl)oxazoline cycloiridated to give only the S,Sp,SIr diastereoisomer. Substitution reactions of the title complexes at iridium proceeded with retention of configuration, a computational study revealing the proposed coordinatively unsaturated intermediate of a dissociative mechanism to display a relatively weak Co-Ir interaction, and a pronounced steric effect as the basis of stereocontrol

Application of a ferrocene-based palladacycle precatalyst to enantioselective aryl-aryl Kumada coupling

The palladium catalysed reaction of 1-iodo-2-methylnaphthalene and 2-methyl-1-naphthylmagnesium bromide gave quantitatively an ( S a )-configured cross-coupled product in 80% e.e. using ( R , S p )-PPFA as a ligand. N , N -Dimethylaminomethylferrocene was cyclopalladated (Na 2 PdCl 4 , ( S )-Ac-Phe-OH, 93% e.e., as determined by 1 H NMR as a result of self-induced non-equivalence), and the resulting ( S p )-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 ( S p )-configured product in up to 71% e.e

Stereoselective Synthesis of All Possible Phosferrox Ligand Diastereoisomers Displaying Three Elements of Chirality:Stereochemical Optimization for Asymmetric Catalysis

All four possible diastereoisomers of phosphinofer- rocenyloxazoline (Phosferrox type) ligands containing three elements of chirality were synthesized as single enantiomers. The S-c configured oxazoline moiety (R = Me, i-Pr) was used to control the generation of planar chirality by lithiation, with the alternative diastereoisomer formed by use of a deuterium blocking group. In each case subsequent addition of PhPCl2 followed by o-TolMgBr resulted in a single P-stereogenic diastereoisomer (S-c,S-p,S-phos and S-c,S-p,R-phos,R- respectively). The alternative diastereoisomers were formed selectively by addition of o-TolPCl(2) followed by PhMgBr ((S-c,S-p,R-phos and S-c,S-p,S-phos,S- respectively). Preliminary application of these four ligand diastereoisomers, together with (S-c,S-p) and (S-c,R-p) Phosferrox PPh2, to palladium catalyzed allylic alkylation of trans-1,3-diphenylallyl acetate revealed a stepwise increase/decrease in ee, with the configuration of the matched/matched diastereoisomer as S-c,S-p,S-phos (97% ee)

Ferrocenyloxazoline-Derived Planar Chiral Palladacycles: C–H Activation, Transmetalation, and Reversal of Diastereoselectivity

Reinvestigation of the palladation of (S)-2-ferrocenyl-4-(methylethyl)oxazoline with Pd(OAc)2 in CH2Cl2 was found to proceed with a dr of 3.6:1 in favor of the resulting S,Sp palladacycle. A similar 4:1 dr was obtained using Na2PdCl4 in MeOH. As an alternative approach, highly diastereoselective lithiation (dr >100:1) and transmetalation were investigated. Addition of PdX2(COD) (X = Cl, Br) to (S,Rp)-2-lithio-1-(2′-(4′-methylethyl)oxazolinyl)ferrocene resulted in double halide substitution and formation of cis-(S,S,Sp,Sp)-bis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]palladium(II) (42% from X = Cl, 50% from X = Br). Selective monoprotodepalladation with HCl gave an S,Sp palladacycle containing a removable ferrocenyloxazoline ligand. Addition of PdCl2(MeCN)2 to mercuracycles in acetonitrile, themselves generated from Li–Hg transmetalation, followed by a brine wash gave (S,Sp)-di-μ-chlorobis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]dipalladium(II) as a single diastereoisomer in high yield. The alternative S,Rp diastereoisomer was obtained in the same way by use of a deuterium blocking group to reverse lithiation diastereoselectivity

Copper(I) complexes of P-stereogenic Josiphos and related ligands

Starting from (R)-Ugi's amine, diastereoselective lithiation followed by Ar'PCl 2 and then Ar’’MgBr led to the generation, as single diastereoisomers, of (R,S p,S phos) [Ar’=Ph, Ar’’=o-Tol] and (R,S p,R phos) [Ar’=o-Tol, Ar’’=Ph] PPFA ligand derivatives. Amine substitution of both with HPCy 2 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 PCl 3. 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

Metallocene to metallocene conversion. Synthesis of an oxazoline-substituted pentamethyliridocenium cation from a ferrocenyloxazoline

Reaction of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline with [(CpIrCl2)-Ir-star](2) in benzonitrile with KPF6 and NaOH gave (eta(5)-(S)-2-(4-(1-methylethyl))oxazolinylcyclopentadienyl)(eta(5)-pentamethylcyclopentadienyl)-iridium(III) hexafluorophosphate (68%). This transformation of an iron-based into an iridium-based metallocene proceeds via the rearrangement, with loss of cyclopentadienyliron, of an intermediate cationic ferrocenyliridacycle

What is Donald Trump?:Forms of 'Celebrity' in Celebrity Politics

It is widely assumed that Donald Trump is a ‘celebrity politician’, and that he has cashed in his success on the reality show The Apprentice to secure political credibility and attention. In this respect he fits what Matthew Wood et al (2016) have labelled the ‘superstar celebrity politician’. This characterisation is the latest in a number of refinements to the definition and understanding of the celebrity politician. While this is a helpful move, I want to suggest that it might overlook one key dimension of the phenomenon. Definitions of the celebrity politician tend to focus on the source of their ‘celebrity’ – how they became famous, rather than on how they act out their celebrity role. This latter dimension features in media coverage, where journalists and commentators borrow from showbusiness to describe politics, but is less often analysed in the political science literature. It matters because, I want to suggest, celebrity politicians like Trump act as stars, whether of reality television, rock music or film. They do not just resemble stars; they are them. This is evident in how they are represented, how they perform and how their ‘fans’ respond to them. It is also symptomatic of wider changes in the conduct and form of the contemporary, mediatised political realm