Cascade Synthesis of Pyrrolo[1,2-a]quinolines and Pyrrolo[2,1-a]isoquinolines via Formal [3 + 2]-Cycloaddition of Push-Pull Nitro Heterocycles with Carbonyl-Stabilized Quinolinium/Isoquinolinium Ylides.

Various substituted pyrrolo[1,2-a]quinolines and pyrrolo[2,1-a]isoquinolines were synthesized in good to high yields by the Et3N-mediated reaction of push-pull 3-nitrobenzofurans or 1-Ts-/1-Ms-3-nitroindoles and precursors of carbonyl-stabilized quinolinium and isoquinolinium ylides as 1,3-dipole equivalents. These transformations proceed in a one-pot manner starting with the formal [3 + 2]-cycloaddition stage, which is accompanied by double dearomatization of both quinoline/isoquinoline and benzofuran/indole moieties, followed by ring-opening of cyclic intermediate formed and nitrous acid elimination sequence. [3 + 2]-Cycloadducts were isolated as the final products in cases of impossibility or difficulty of their enolization. The present protocol was successfully extended to 3-nitro-4H-chromene derivatives as push-pull dipolarophile component. Finally, using the method of competing reactions, the reactivity of the starting compounds was compared with each other.

New Calix[4]arene-Fluoresceine Conjugate by Click Approach-Synthesis and Preparation of Photocatalytically Active Solid Lipid Nanoparticles.

New fluorescent systems for photocatalysis, sensors, labeling, etc., are in great demand. Amphiphilic ones are of special interest since they can form functional colloidal systems that can be used in aqueous solutions. A new macrocycle platform for click chemistry and its adduct with o-propargylfluoresceine was synthesized and characterized using modern physical techniques. Nanosized solid lipid nanoparticles (SLNs) from the calixarene-fluoresceine adduct were synthesized through the solvent injection technique and well-characterized in the solution and in solid state using light-scattering and microscopy methods. The maximum fluorescence intensity of the SLNs was found to be in the pH range from 7 to 10. The Förster resonance energy transfer (FRET) efficiency from SLNs to rhodamine 6g was found to be 97.8%. Finally, pure SLNs and the FRET system SLNs-Rh6G were tested in model photocatalytic ipso oxidative hydroxylation of phenylboronic acid under blue LED light. The SLNs-Rh6G system was found to be the best, giving an almost qualitative phenol yield, which was shown by HPLC-UV analysis.

Catalyst-free formal [3 + 2] cycloaddition of stabilized N,N-cyclic azomethine imines to 3-nitrobenzofurans and 3-nitro-4H-chromenes: access to heteroannulated pyrazolo[1,2-a]pyrazoles.

We have studied the [3 + 2]-cycloaddition of various N,N-cyclic azomethine imines to 3-nitrobenzofurans. This process is a rare example of their dearomatization. We have also extended this process to the related 3-nitro-4H-chromenes as dipolarophiles. Both reactions provide access to benzofuro- and chromeno-condensed pyrazolo[1,2-a]pyrazoles with 100% atom economy in a diastereoselective manner under mild eco-friendly conditions. Finally, on the basis of DFT calculations, the mechanistic insights into the mentioned [3 + 2]-cycloadditions and explanations of the experimentally determined limitations of the method are given. Hirshfeld atomic charge values of push-pull heterocycles were suggested as a criterion for a priori assessment of the possibility of their dipolar cycloaddition with N,N-cyclic azomethine imines.