Theoretical conformational study of six-membered cyclic allyl epoxides

Accurate “ab initio” calculations (MP2 method) were performed to outline the conformational profile of a number of six-membered cyclic allyl epoxides differing either in the nature of the cycle fragment (Y) bound to the unsaturation, or in the substitution at the endocyclic carbon bound to the epoxy ring and bridging the epoxy ring with the Y fragment. In particular, we calculated structures 4 (Y=CH₂), 5 (Y=O), 6 (Y=NH), 7 (Y=S), 8 (Y=CF₂), 9 (Y=NH₂ ⁺), 10 (Y=CO), 11 (Y=BH) and 12 (Y=NCOOH), where the fragment of the endocyclic carbon bridging “Y” and the epoxy fragment is either non-substituted (4a – 12a) or bears a methyl side chain trans (4b–12b) or cis (4c–12c) to the epoxidic oxygen. Saturated analogs (Y=O and Y=CH₂) were also computed to test the method and to evaluate the conformational profile in the absence of the unsaturation. Minimum energy conformations were found which differ in the relative position of the Y group and the epoxy oxygen, with respect to a plane containing the epoxy ring carbons and the adjacent saturated endocyclic carbon: they may be on the same side (conformer A) or on opposite sides (conformer B). Conformers A are generally more stable. The conjugation effect of Y with the double bond lowers the barrier between the two conformers to the extent that in a few cases only conformer A is associated with a minimum of energy. On the basis of the elongation of the allylic oxirane C–O bond, we postulated the order of reactivity of epoxides 4–12 in the oxirane ring-opening process, and a mechanism based on the more reactive conformer A. A comparison was also made between MP2 and DFT calculation methods.     

Diketopyrrolopyrrole Bis-Phosphonate Conjugate: A New Fluorescent Probe for In Vitro Bone Imaging

The synthesis of a conjugate molecule between an unusual red-fluorescent diketopyrrolopyrrole (DPP) unit and a bis-phosphonate (BP) precursor by a click-chemistry strategy to target bone tissue and monitor the interaction is reported. After thorough investigation, conjugation through a triazole unit between a γ-azido rather than a β-azido BP and an alkyne-functionalized DPP fluorophore group turned out to be the winning strategy. Visualization of the DPP-BP conjugate on osteoclasts and specific antiresorption activity were successfully demonstrated.     

Millimeter-wave investigation, simplified interpretation of the fourfold rotational spectrum, and dynamics of the internal motions of acetaldehyde-argon

The rotational spectra of the acetaldehyde-argon van der Waals complex have been measured by free jet absorption millimeter-wave spectroscopy in the frequency range 60-78 GHz. Each rotational transition is split into four hyperfine component lines, which is evidence of the occurring of two different internal motions. The splittings have been interpreted in terms of a coupled Hamiltonian that precisely determines the separation of energy levels due to the tunneling of the rare gas atom between two equivalent minima, while the information on the barrier to internal rotation of the methyl group is obtained from the pattern of the component A-E lines due to this motion. The interaction of the rare gas atom with the acetaldehyde moiety is reflected in a reduction of the V₃ barrier to internal rotation in going from the molecule to the weakly bound complex of about 20%. The barrier to the Ar tunnelling has been estimated to be 26 cm⁻¹.     

Intertorsional Interactions Revealing Absolute Configurations: The V6 Internal Rotation Heavy‐Top Case of Benzotrifluoride

The microwave spectroscopic signatures of multiple torsional states of the CF₃ internal rotation in benzotrifluoride (α,α,α‐trifluorotoluene) are reported. Individual rotational transitions are observed in a total of eight different torsional states, a quite challenging task for heavy tops even with Fourier transform microwave techniques. Accidental mixings of m=0 and m=3 torsional states as well as m=1 and m=2 torsional states, which can complicate the assignment of the spectra severely, are observed. These accidental mixings are probably systematic for molecules with heavy tops exhibiting an almost free internal rotation, and give an opportunity to determine the sign in the (1/2) V₆ (1±cos6τ) potential function hindering internal rotation and in consequence the orientation of the CF₃ top versus C₆H₅ frame. A recently developed torsion–rotation program reproduces all line positions within an experimental accuracy of about 2.0 kHz. The V₆ barrier is determined to be 3.229949(32) cm^?1. The corresponding torsional spacings are determined with the seven‐digit accuracy underlying the supersonic‐jet Fourier transform microwave technique.     

Stereoselective uncatalyzed synthesis of 2,3-unsaturated-4-n-substituted-beta-O-glycosides by means of a new D-galactal-derived N-(mesyl)-aziridine

The reaction of the new D-galactal-derived allylic aziridine 1beta with O-nucleophiles (alcohols and monosaccharides) affords, in a high to complete beta-stereoselectivity, the corresponding 2,3-unsaturated-beta-O-glycosides bearing a beta-N-functionality at C4.     

Mechanism of oxidative addition of benzonitriles to DI(1,4-bis(diethylphosphino)butane)nickel(0)

A kinetic study of the oxidative addition of RC₆H₄CN (R = H, m-CN, p-CN) to Ni(DEPB)₂ (DEPB = 1,4-bis(diethylphosphino)butane) suggests a template mechanism leading to the fission of one C---CN bond. The reaction products are trans-planar cyano-organonickel(II) complexes, Ni₂(μ-DEPB)₂(RC₆H₄)₂(CN)₂ and Ni(η¹- DEPB)(RC₆H₄)(CN), in equilibrium. through exchange of DEPB.