Regio- and Stereoselective Synthesis of Spiropyrrolizidines and Piperazines through Azomethine Ylide Cycloaddition Reaction.

A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused piperazines through a stepwise [3 + 3] cycloaddition pathway is observed. The stereochemistry of these N-heterocycles has been confirmed by several X-ray diffraction studies. Some of these compounds exhibit extensive hydrogen bonding in the crystalline state. To enlighten the observed regio- and stereoselectivity of the [3 + 2] cycloaddition, calculations using the DFT approach at the B3LYP/6-31G(d,p) level were carried out. It was found that this reaction is under kinetic control.

New insights into the thermal stability of the smectic C phase.

Subtle differences in the molecular structure of mesogens can lead to very different experimental polymorphisms. The smectic C (SmC) phase can actually be exhibited by one isomer and not the other, or the range of temperature can be completely different. Unveiling the deep connection between atomic structure and the very existence of the SmC phase will lead to the design of new performing liquid crystalline materials for ferroelectric or nonlinear optical applications. Our approach is based on running molecular dynamics simulation from an initial SmC arrangement of molecules. When the temperature is increased, the molecules automatically adjust in a more favorable organization. Such modification in the imposed initial self-assembly is governed by values of the nonbonded energies. Thanks to the combined use of simulation and experimental phase diagrams, we have unveiled part of the deep connection between atomic structure and the very existence of the SmC phase. The actual display of the SmC mesophase stems from a subtle balance between short-range interactions, which reveal arrangement of molecules within a smectic layer, and long-range interactions, which disclose organization of layers.

Dissociative adsorption of hydrogen fluoride onto amorphous solid water.

Adsorption of hydrogen fluoride (HF) onto amorphous solid water films at 50 K is reported to yield a strong absorbance continuum in their reflection-absorption infrared spectra (RAIRS). This and other complex features observed in the RAIRS spectra of stratified binary composite HF:H(2)O nanoscopic films deposited onto Pt(111) are interpreted quantitatively using a classical optics model. Comparison with experimental data allows us to determine that the absorbance continuum is due to absorption within the film (as opposed to trivial optical effects) and that the extent of intermixing and uptake is mostly limited to the first few molecular layers. Furthermore, extensive isotope scrambling is demonstrated by the observation of similar Zundel continua upon codeposition of neat HF, or DF, and H(2)O vapors onto Pt(111) at 50 K. These observations are consistent with those expected from extensive ionic dissociation of HF upon dissolution within, and adsorption onto, ASW at 50 K.