Gérald Bernardinelli

Absolute structure and absolute configuration

Fundamental notions concerning absolute structure and absolute configuration, and their determination from single-crystal diffraction measurements, are presented and reviewed. A glossary of terms with definitions useful in this field is provided. For absolute structure and its determination, the separate but interacting influences of the structure and the inversion-distinguishing power of an X-ray diffraction experiment with dispersive scatterers are examined. Important experimental and algorithmic details of the current methods used for absolute-structure determination are provided. Characterization of crystals for absolute-structure determination and of molecules for absolute-configuration determination are treated. Attention is given to the analysis of absolute structure and absolute configuration in twinned crystals.

Stereoselective Synthesis of Coordination Compounds: Self-Assembly of a Polymeric Double Helix with Controlled Chirality.

Its information content is infinitely smaller than that of DNA, but its structure (see picture) ressembles the double-stranded helix produced by nature. This self-assembled, configurationally predetermined coordination polymer is built up from enantiopure chiral bipyridine-type ligands and silver ions.

Enantioselective Organocatalytic Conjugate Addition of Aldehydes to Vinyl Sulfones and Vinyl Phosphonates as Challenging Michael Acceptors

Chiral framework: Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to >99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.Chiral amines with a pyrrolidine framework catalyze the enantioselective conjugate addition of a broad range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to >99 % ee. This novel process provides synthetically useful chiral gamma-gem-sulfonyl or phosphonyl aldehydes which can be widely functionalized with retention of the enantiomeric excess. Mechanistic insights including DFT calculations are explored in detail.

Manzamine B and C, two novel alkaloids from the sponge haliclona sp.

Abstract The title compounds were isolated from a marine sponge collected off Okinawa. Their structures were determined by X-ray and shown to be 1-β-carbolines. Manzamine C was the 2-ethyl-N-azacycloundec-6-ene derivative, whereas manzamine B was more complex being the epoxy isomer of the free base of dihydromanzamine A.

Naphthalene Complexes. V. Arene Exchange Reactions in Naphthalenechromium Complexes

Abstract Di-η 6 -naphthalenechromium(0) ( 1 ) reacts at 150°C with benzene to yield (η 6 -naphthalene)(η 6 -benzene)chromium(0) ( 3 ) in 76% yield. In the presence of THF, 1 undergoes Lewis base catalyzed arene exchange at 80°C. Reactions of 1 with substituted arenes yield the mixed sandwich complexes 4 and 6–10 (arene = 1,4-C 6 H 4 Me 2 , 1,3,5-C 6 H 3 Me 3 , C 6 Me 6 , 1,4-C 6 H 4 (OMe) 2 , 1,4-C 6 H 4 F 2 and 1,4-C 10 H 6 Me 2 ). In all but one case (with 1,4-dimethylnaphthalene) exchange of a single naphthalene ligand is observed. In marked contrast to the lability of 1 , dimesitylenechromium(0) ( 5 ) is inert to arene displacement in benzene up to 240°C. The molecular structure of 3 has been determined by X-ray crystallography. The crystal data are as follows: a 7.784(1), b 13.411(2), c 22.772(5) A, Z = 8, space group Pbca . The structure was refined to a R w value of 0.043. The naphthalene ligand in 3 is nearly planar and parallel to the approximately eclipsed benzene ring. Metal atom-ring distances are 1.631(9) and 1.611(4) A for naphthalene and benzene, respectively. Catalyzed and uncatalyzed naphthalene exchanges in the sandwich complex are compared to the analogous reactions with the Cr(CO) 3 complex 2 . Naphthalene exchange in 2 in benzene is 10 3 to 10 4 times faster than arene exchange in other arenetricarbonylchromium compounds. The mild conditions for Lewis base catalyzed naphthalene exchange make 2 a good precursor of other arenetricarbonylchromium compounds. Examples include the Cr(CO) 3 complexes of styrene, benzocyclobutene, 1-ethoxybenzocyclobutene, 1,8-dimethoxy-9,10-dihydroanthracene and 1,4-dimethylnaphthalene.

Chiral toluene-2,α-sultam auxiliaries: Preparation and structure of enantiomerically pure (2R)- and (S)-ethyl-2,1′-sultam ☆

Abstract Crystalline sultams (R)- 2 or (S)- 2 were selectively prepared from prochiral saccharine ( 3 ) in two steps (53% overall yield) via Ru-(R)-BINAP- or Ru-(S)-BINAP catalyzed asymmetric hydrogenation of imine 4 . Alternatively, pure (R)- 2 was synthesized (37% overall yield) from (R)-α-phenethylamine in 4–5 steps involving the ortho-sulfination 6 → 7 and the highly diastereoselective cyclization of sulfinic acid 7 to the sulfinamide 8 . X-ray diffraction analyses of sulfinamide 8 and sultam (R)- 2 are presented.

Completely Stereospecific Self-Assembly of a Circular Helicate

A nanoscale turbine wheel is an apt description of the structure of the enantiomerically pure helicate [Ag6 (L2)6 ]6+ (1), which precipitates as PF6 salt on mixing dissolved AgPF6 with the ligand L2 (a bis-bidentate ligand comprising two condensed α-pinene/bipyridine units linked by a xylylene bridge). The helicate has an outer diameter of about 3 nm and an inner diameter of 0.84 nm, and is a potential model for the study of stereospecific recognition processes.

Venustatriol. A new, anti-viral, triterpene tetracyclic ether from Laurencia venusta

Abstract Venustatriol, a new tetracyclic ether derived from squalene, which has anti-viral activity, has been isolated from the red alga Laurencia venusta . Its structure and absolute configuration were determined by X-ray using the absolute structure parameter x. By comparison of their spectral properties, the absolute configuration of its congener, thyrsiferol, was deduced.

C3 Vanadium(V) Amine Triphenolate Complexes: Vanadium Haloperoxidase Structural and Functional Models

The C 3 vanadium(V) amine triphenolate complex 1f has been characterized as a structural and functional model of vanadium haloperoxidases. The complex catalyzes efficiently sulfoxidations at room temperature using hydrogen peroxide as the terminal oxidant, yielding the corresponding sulfoxides in quantitative yields and high selectivities (catalyst loading down to 0.01%, TONs up to 9900, and TOFs up to 8000 h (-1)) as well as bromination of 1,3,5-trimethoxybenzene (catalyst loading down to 0.05%, TONs up to 1260, and TOFs up to 220 h (-1)).

Asymmetric diels-alder reactions : facile preparation and structure of sulfonamido-isobornyl acrylates

Abstract The crystalline chiral auxiliaries 2 , 3 and 4 were prepared from camphor-10-sulfonyl chlorides in 2 steps. Their readily accessible acrylates underwent efficient asymmetric diels-alder additions to cyclopentadiene, the topicity of which agrees with X-ray evidence.