Structure and Conformation of Novel BODIPY Ugi Adducts.

Two novel BODIPY-Ugi (boron dipyrromethene) adducts exhibit peculiar room temperature (T=20 °C) H-1 NMR spectra in that several protons located at the aromatic aniline-type ring are lost in the baseline. This observation revealed the existence of a dynamic conformational process where rotation around the C-N bond is hindered. Variable-temperature H-1 and C-13 NMR spectroscopic analysis confirmed this conclusion; that is, low-temperature spectra show distinct signals for all four aromatic protons below coalescence, whereas average signals are recorded above coalescence (T=+120 °C). Particularly interesting was the rather large difference in chemical shifts for the ortho protons below coalescence, Δδ=1.45 ppm, which was explained based on DFT computational analysis. Indeed, the calculated lowest-energy gas-phase conformation of the BODIPY Ugi adducts locates one half of the aniline-type ring in the shielding anisotropic cone of the bridge phenyl ring in the BODIPY segment. This is in contrast to the solid-state conformation established by X-ray diffraction analysis that shows a nearly parallel arrangement of the aromatic rings, probably induced by crystal packing forces.

Novel Methodologies for Chemical Activation in Organic Synthesis under Solvent-Free Reaction Conditions.

One central challenge for XXI century chemists is the development of sustainable processes that do not represent a risk either to humanity or to the environment. In this regard, the search for more efficient and clean alternatives to achieve the chemical activation of molecules involved in chemical transformations has played a prominent role in recent years. The use of microwave or UV-Vis light irradiation, and mechanochemical activation is already widespread in many laboratories. Nevertheless, an additional condition to achieve "green" processes comes from the point of view of so-called atom economy. The removal of solvents from chemical reactions generally leads to cleaner, more efficient and more economical processes. This review presents several illustrative applications of the use of sustainable protocols in the synthesis of organic compounds under solvent-free reaction conditions.