Paul A. Gugger

Facile interconversions between diastereomers of chloro-bridged palladium(II) dimers of orthometallated (±)-dimethyl[1-(1-naphthyl)ethyl]amine

Abstract The important chloro-bridged dipalladium(II) resolving agents (R,R)- and (S,S)-cis-di-μ-chlorobis[1-[1-(dimethylamino)-ethyl]-2-naphthalenyl-C,N]dipalladium, (R,R)- and (S,S)-cis-1, undergo facile rearrangements into unequal mixtures of cis and trans diastereomers upon dissolution in chloroform or dichloromethane, although concentration of the solution in each case affords in high yield the pure cis diastereomer of the dinuclear metal complex as the corresponding mono-solvate in a typical second-order asymmetric transformation. When equimolar solutions of (R,R)-cis- and (S,S)-cis-1 CH2Cl2 in dichloromethane are mixed together, however, an equilibrium is rapidly established between the cis and trans diastereomers of the (R ∗ ,R ∗ )-(±) and ( R ∗ ,S ∗ ) forms of 1 and from which solution configurationally homogeneous (R ∗ ,S ∗ )-trans- 1 · CH 2 Cl 2 crystallizes in high yield by second-order asymmetric transformation. The crystal and molecular structures of (R,R)-cis- 1 · CH 2 Cl 2 and (R ∗ ,S ∗ )-trans- 1 · CH 2 Cl 2 have been determined. The optical purities of the individual enantiomers of (R ∗ ,R ∗ )-(±)- 1 · CH 2 Cl 2 have been determined by reaction with (1R,2S,5R)-menthyldiphenylphosphine or (1S, 2S, 5R)-neomenthyldiphenylphosphine in chloroform-d1 and analysis of the 31P1H NMR spectra of the resulting solutions of the corresponding bridge-split palladium(II)-phosphine epimers.

Configurationally homogeneous diastereomers of a linear hexa(tertiary phosphine): Enantioselective self-assembly of a double-stranded parallel helicate of the type (P)-(Cu 3 (hexaphos) 2 )(PF 6 ) 3

Three configurationally homogeneous diastereomers of the linear hexa(tertiary phosphine) Ph2PCH2CH2P(Ph)CH2CH2P(Ph)CH2CH2P(Ph)CH2CH2P(Ph)CH2CH2PPh2 (hexaphos) have been isolated in enantiomerically pure form, namely (R,S,S,R)-, (R,S,S,S)-, and (S,S,S,S)-hexaphos. The strongly helicating (R,S,S,R)-(−) form of the ligand combines with copper(I) ions to generate by stereoselective self-assembly the P enantiomer of a parallel helicate of the type [Cu3(hexaphos)2](PF6)3, which has been characterized by x-ray crystallography. Theoretical modeling of the cation indicates that it is the relationship between the helicities of the two 10-membered rings containing the three copper ions, each of which has the twist-boat–chair–boat conformation, and the configurations of the three chiral, tetrahedral copper stereocenters of P configuration that determines the stereochemistry of the parallel and double α-helix conformers of the double-stranded trinuclear metal helicate.

Enantioselective synthesis of a conformationally rigid, sterically encumbered, 2-arsino-7-phosphanorbornene.

Convenient access to the enantiomerically pure, conformationally rigid, ligand [5-(dicyclohexylarsino)-2,3-dimethyl-7-phenyl-7phosphabicyclo[2.2.1]hept-2-ene has been established by intramolecular [4 + 2]-Diels–Alder cycloaddition between dicyclohexylvinylarsine and 3,4-dimethyl-1-phenylphosphole using chiral organopalladium(II) complexes containing orthometallated (S)-1--(dimethylamino)ethylnaphthalene or (R)-2--(dimethylamino)ethylnaphthalene as the reaction templates. The ligand was displaced from the palladium complex with cyanide and reacted with [( 6 -arene)RuCl2]2 and NH4PF6 to form diastereomeric [( 6 -arene)Ru(PAs)Cl]PF6 complexes, chiral at ruthenium. New complexes have been characterized by elemental analyses, electrochemistry, and electronic, circular dichroism, 1 H-, 1 H{ 31 P}-, 13 C{ 1 H}- and 31 P{ 1 H}-NMR spectroscopies, and in several cases, by X-ray crystallography.

Phenylphosphonate Transport by Helicobacter pylori

Background:  Helicobacter pylori can utilize phenylphosphonate as a sole source of phosphorus, and it is able to transport the phosphonate N‐phosphonoacetyl‐L‐aspartate. However, H. pylori does not have any genes homologous to those of the known pathways for phosphonate degradation in bacteria, indicating that it must have novel pathways for the transport and metabolism of phosphonates.

Enantioselective biotransformation of ethyl-n-propylarsinic acid by the mould Scopulariopsis brevicaulis: asymmetric synthesis of (R)-ethylmethyl-n-propylarsine

The mould Scopulariopsis brevicaulis, when growing on bread containing ethyl-n-propylarsinic acid, produces R-ethylmethyl-n-propylarsine of 60% optical purity.