D. S. Yufit

The CF bond as a tool in the conformational control of amides

Abstract The conformation of 2-fluoro- N -(2-fluoroethyl)-propionamide 4 in the solid state indicates the influence of both a β-fluorine-amide gauche effect and an α -fluoroamide effect. The structure reveals the influence of two recently observed stereoelectronic effects associated with the CF bond, which has resulted in the successful prediction of the solid state conformation of amide 4. A gauche relationship (−69.9°) was observed for atoms N(1)C(4)C(5)F and a syn planar (2.0°) relationship was observed for N(1)C(3)C(2)F. The paper demonstrates the predictive power of using the CF bond as a tool in influencing the conformation of amides and peptides.

Palladium-Catalyzed C—F Activation of Polyfluoronitrobenzene Derivatives in Suzuki—Miyaura Coupling Reactions

Highly fluorinated nitrobenzene derivatives are suitable substrates for palladium-catalyzed C-F bond arylation using readily available palladium catalysts under both conventional heating and microwave conditions. Arylation occurs ortho to the nitro group offering a synthetic route to polyfluorinated 2-arylnitrobenzene systems. The regiochemistry of the arylation reactions suggests that there is a significant directing interaction between the nitro group and the incoming nucleophilic palladium catalyst which is facilitated by the presence of several fluorine atoms attached the ring. Investigations into the regioselectivity and reactivity of several tetrafluoro- and trifluoronitrobenzene derivatives provides further evidence for the highly nucleophilic character of the oxidative addition step in contrast to the concerted mechanism of more conventional Suzuki-Miyaura coupling reactions involving aryl iodides and bromides.

Polyhalogenated heterocyclic compounds. Macrocycles from perfluoro-4-isopropylpyridinePart 50. For part 49 see ref. 1.

Perfluoro-4-isopropylpyridine was used as a building block for the two-step synthesis of a variety of macrocyclic systems bearing pyridine sub-units which were characterised by X-ray crystallography. Electrospray mass spectrometry revealed that complexation of either cations and, unusually, anions is possible depending on the structure of the macrocycle.

Triangular W3S74+ and W3S44+ complexes

Abstract Methods for the synthesis of triangular thiohalogenide complexes of tungsten W 3 S 7 X 4 (XCl, Br) proceeding from metallic tungsten or WS 3 have been developed. Ways have been found for converting these polymeric complexes to triangular W 3 S 7 X 6 2− complexes which preserve the architecture of the W 3 (μ 3 -S)(μ 2 -S 2 ) 3 4+ cluster fragment. Heating W 3 S 7 X 4 in a PPh 4 X melt or in concentrated acids HX in the presence of Et 4 NX afforded PPh 4+ and Et 4 N + salts of W 3 S 7 X 6 2− (XCl, Br). The structure of (Ph 4 P) 2 W 3 S 7 Br 6 ( III ) was established by X-ray diffraction analysis. The crystals of III are orthorhombic, a =18.082(2), b =25.834(3), c =27.370(2) A, Z =8, Pbca , R ( R w )=0.049 (0.055). The Et 4 N + salt of W 3 34 S 7 Br 6 2− has been obtained and a calculation of the normal vibrations has been performed for W 3 S 7 Br 6 2− . Interaction of W 3 S 7 Br 4 , with a KNCS melt or an aqueous solution of (NH 4 ) 2 S x involves transformation of the cluster fragment W 3 S 7 4+ to a W 3 S 4 4+ fragment to produce W 3 S 4 (NCS) 9 5− and W 3 S 4 (S 4 ) 3 (NH 3 ) 3 2− complexes. The structure of (NH 4 )(H)(H 2 O) 3 W 3 S 16 (NH 3 ) 3 ( VI ) was established by X-ray diffraction analysis. The crystals of VI are trigonal, a =12.508(1), c =10.112(1) A, Z =2, P 31 c , R ( R w )=0.029 (0.033).

The First Enantiomerically Pure Triangulane (M)‐Trispiro[2.0.0.2.1.1]nonane Is a σ‐[4]Helicene

A remarkably high specific rotation, even at 589 nm, is shown by (M)-1, the first enantiomerically pure unbranched [4]triangulane, although it has no chromophore that would lead to any significant absorption above 200 nm. This outstanding rotatory power is in line with a helical arrangement of its σ bonds, as confirmed by high-level computations. Thus, it is appropriate to call (M)-1 a “σ-[4]helicene”, the first σ-bond analogue of the aromatic [n]helicenes.

Electron distribution and molecular motion in crystalline benzene : an accurate experimental study combining CCD X-ray data on C6H6 with multitemperature neutron-diffraction results on C6D6.

The electronic properties of the benzene molecule, for example its quadrupole moment and the electric field gradients (EFGs) at the H nuclei, are of fundamental importance in theoretical and experimental chemistry. With this in mind, single-crystal X-ray diffraction data on C(6)H(6) were collected with a charge-coupled device detector at T approximately 110 K. As accurate modelling of the thermal motion in the crystal was regarded as vital, especially for the hydrogen atoms, anisotropic-displacement parameters (ADPs) for the C and H atoms in C(6)H(6) were derived in a straightforward fashion from analysis of the temperature dependence of ADPs for the C and D atoms in C(6)D(6) at 15 K and 123 K obtained by neutron diffraction. Agreement between C-atom ADPs derived from thermal-motion analysis of neutron data and those obtained from multipole refinement by using the X-ray data is extraordinarily good; this gives confidence in the modelling of vibrational motion for the H atoms. The molecular quadrupole moment derived from the total charge density of the molecule in the crystal is (-29.7+/-2.4)x10(-40) C m(2), in excellent agreement with measurements made in the gas phase and in solution. The average deuterium nuclear quadrupole coupling constant (DQCC) derived from EFG tensors at H atoms is 182+/-17 kHz, also in excellent agreement with independent measurements. The strategy employed in this work may be of more general applicability for future accurate electron density studies.

Synthesis, structure, vibrational spectra and chemical properties of the triangular molybdenum and tungsten complexes M3(μ3-S)(μ2-SSe)3X62− (M = Mo, W; X = Cl, Br)

Abstract Salts containing M3(μ3-S)(μ2-S2)3X62− (M = Mo, W; X = Cl, Br) anions interact with SePPh3 upon heating in acetonitrile to form SPPh3 and M3(μ3-S)(μ2-SSe)3X62−. The stereochemisty of this reaction has been studied. In the reaction of SePPh3 with Mo3(μ3-34S)(μ2-34Sa32Se)3X62− replacement of the equatorial sulfur atoms takes place, and 32SPPh3 and Mo3(μ3-34S)(μ2-34SaSee)3X62− are produced. The structure of (PPh3Et)2Mo3(μ3-S)(μ2-SSe)3Cl6 (I) was established by X-ray diffraction analysis. The crystals of I are triclinic, space group P 1 (a = 13.547(2), b = 13.755(2), c = 15.736(3) A; α = 101.79(1), β = 97.71(1), γ = 110.49(1)°, Z = 2). A total of 5721 independent reflections has been collected on an automated diffractometer, and the structure was solved to R = 0.051 (Rw = 0.062). The selenium atoms are essentially in the plane of the Mo3 triangle. The SSe distances are 2.157(5)–2.163(4) A. Complex I is the first compound containing a SSe ligand that has been structurally characterized. IR and Raman spectra of M3S4Se3X62− have been studied. For Mo3S4Se3Cl62− an analysis of the normal vibrations has been performed. The force constant of the SSe bond in complex I is 2.3 mdyn/ A. Heating of (Et4N)2Mo3S4Se3Br6 under vacuum at 450 °C gave rise to MoSSe.

Continuous gas/liquid–liquid/liquid flow synthesis of 4-fluoropyrazole derivatives by selective direct fluorination

Summary 4-Fluoropyrazole systems may be prepared by a single, sequential telescoped two-step continuous gas/liquid–liquid/liquid flow process from diketone, fluorine gas and hydrazine starting materials.

Das erste enantiomerenreine Triangulan: (M)-Trispiro[2.0.0.2.1.1]nonan ist ein σ-[4]Helicen

Eine auserordentlich hohe spezifische optische Drehung selbst bei 589 nm kennzeichnet (M)-1, das erste enantiomerenreine, unverzweigte [4]Triangulan, obwohl es keinen Chromophor enthalt, der zu einer nennenswerten Absorption oberhalb von 200 nm fuhren wurde. Diese hohe spezifische Drehung hat mit der helicalen Anordnung der σ-Bindungen zu tun, was durch Rechnungen auf hohem Niveau bestatigt wird. Damit erscheint es gerechtfertigt, das [4]Triangulan in Analogie zu den aromatischen π-[n]Helicenen als σ-[4]Helicen zu bezeichnen.

3‐Azabicyclo[3.1.0]hex‐1‐ylamines by Ti‐Mediated Intramolecular Reductive Cyclopropanation of α‐(N‐Allylamino)‐Substituted N,N‐Dialkylcarboxamides and Carbonitriles

A variety of tris- and monoprotected derivatives with the 1-amino-3-azabicyclo[3.1.0]hexane and 1-amino-3-azabicyclo[4.1.0]heptane skeleton 10 have been synthesized by intramolecular reductive cyclopropanation of α-(N-allylamino)-substituted N,N-dialkylcarboxamides 6, 8, and 9. Starting from derivatives of the naturally occurring amino acid serine (4a, 4b), the enantiomerically pure compounds 10a and 10b were obtained with endo/exo ratios of 2.5:1 (a) and 2:1 (b), in 26 and 30% overall yields, respectively. The unprotected bicyclic amines 11aa, 11ab, 11ba, and 11ad have been prepared by palladium-catalyzed hydrogenative deprotection of 10aa, 10ab, 10ba and 10ad, respectively, under acidic conditions, in 91, 95, 96, and 99% yields, respectively. X-ray crystal structure analyses of 10aa and 10ad in each case found an equatorial position of the N-benzyl group on the heterocycle and a common boat conformation for the 3-azabicyclo[3.1.0]hexane and 3-azabicyclo[4.1.0]heptane skeletons as a whole. One-step preparations of the bicyclic diamines 11ac (41% yield) and 14a (48% yield) have been performed by application of the Kulinkovich−de Meijere procedure to the nitriles 12a and 12b. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)