María E. Ochoa

A new method for the preparation of unsymmetrical 1,4-substituted piperazine derivatives

Abstract Symmetrical and unsymmetrical N , N ′-piperazine derivatives of (−)-norephedrine and o -aminophenol were synthesized stereoselectively in yields >70% by reduction of the corresponding N , N ′-ethylenebisoxazolidine heterocycles. The stereochemistry at the ring fusion carbons was established by NMR spectroscopy and X-ray crystallography.

Crystalline arrays of molecular rotors with TIPS-trityl and phenolic-trityl stators using phenylene, 1,2-difluorophenylene and pyridine rotators

In this work, we describe the synthesis and solid-state characterization of a series of molecular rotors with tri-isopropylsilyloxy-substituted (TIPS) trityl stators axially linked to 1,4-diethynylphenylene, 3,6-diethynyl-1,2-difluorophenylene and 2,5-diethynylpyridine rotators to produce 1,4-bis[(3,3-diphenyl-3-(3′-(tri-isopropylsilyloxy)-phenyl)-prop-1-yn-1-yl)]benzene (1), 1,4-bis[(3,3-diphenyl-3-(3′-(tri-isopropylsilyloxy)-phenyl)-prop-1-yn-1-yl)]-2,3-difluorobenzene (2) and 2,5-bis[(3,3-diphenyl-3-(3′-tri-isopropylsilyloxy)-phenyl)-prop-1-yn-1-yl)]pyridine (3). The subsequent removal of the TIPS protecting group led to their corresponding hydroxyl-substituted trityl derivatives (4) and (5). TIPS- and HO-substituted stators are involved in different inter- and intramolecular interactions (hydrogen bonding, phenyl embraces, C–H–π interactions) that give rise to isomorphic packing motifs that constrained the rotational dynamics in the solid-state to the slow exchange regime.

Synthesis and Evaluation of Molecular Rotors with Large and Bulky tert-Butyldiphenylsilyloxy-Substituted Trityl Stators

The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with tert-butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor 7c with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue 7c-d(4) by solid state (2)H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-d(4) rotator in the kHz regime.

Designed synthesis of “L” shaped 17-halo-aryl-ethynyl steroids

Thirteen steroidal derivatives were synthesized through a Sonogashira cross-coupling reaction which has been found to be an excellent synthetic strategy to introduce halo-aromatic groups into C-17-ethynyl substituted steroidal frameworks. The structural modification was performed on ethynylestradiol, mestranol, norethisterone, ethisterone and 3-ethynyl-3-epi-sarsasapogenin. The solid state study by X-ray diffraction showed that most of them belong to the orthorhombic P212121 space group and the whole family has an “L” conformation, regardless of the nature of the steroid A-ring (3-hydroxy-aromatic or 3-oxo). Due to the presence of several moieties which are susceptible to forming secondary interactions, the crystalline packing is governed by O–H⋯O, C–H⋯O, and C–H⋯π interactions, and only 17α-(4′-iodophenylethynyl)-3-methoxy-estra-1,3,5(10)-trien-17-β-ol (mestranol derivative 3) showed an iodine–iodine interaction (dI⋯I = 4.116 A). The crystalline packing for ethynylestradiol derivatives 1, 2 and 4 showed the formation of holes with diameters greater than 5.2 A suggesting their potential application in host guest chemistry or as porous materials.

One-pot microwave-assisted synthesis of organotin Schiff bases: an optical and electrochemical study towards their effects in organic solar cells

Four organotin compounds bearing Schiff bases were prepared via a multicomponent microwave-assisted reaction among 2-hydroxy-1-naphthaldehyde, 2-aminophenol derivatives and the corresponding diorganotin oxide (R2SnO, R = nBu or Ph), with high yields and a low economic/environmental impact. All of the compounds were fully characterized by NMR (1H, 13C, and 119Sn) spectroscopy, high-resolution mass spectrometry, X-ray diffraction, cyclic voltammetry, UV/Vis spectroscopy, and fluorescence spectroscopy. All of the compounds absorb in the visible region around 480–490 nm, close to the maximum solar emission, with an optical band gap of around 2.3 eV and low fluorescence quantum yields. According to the electrochemical study, they present LUMO values close to that of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM-C60), a typical electron acceptor organic photovoltaic material. Based on this combined optical/electrochemical study and as it allows the preparation of homogeneous spun films, the n-butyltin complex with carboxylic acid was selected for the investigation of its possible photovoltaic properties in organic solar cells. Charge photogeneration was obtained only using this organotin compound as an electron acceptor material with poly(3-hexylthiophene, P3HT) (typical electron donor material) with an open circuit voltage of 300 mV, a short-circuit current density of 0.11 mA cm−2 and an efficiency of 5.2 × 10−3%. Despite the fact that the efficiency is much lower with respect to the reference device P3HT/PCBM-C60, this preliminary result suggests that, after chemical and device processing optimization, tin complexes with Schiff bases could be applied as electron acceptor materials in organic photovoltaic devices.

Centrosymmetric Binuclear Boron Compounds Derived from Dithiooxamides: Synthesis, Characterization, and Their Photophysical Properties

In this paper, we report the synthesis and characterization of new boron compounds derived from dithiooxamides. The compounds were characterized by NMR (1H and 13C), UV-vis, fluorescence spectroscopy, and high resolution mass spectrometry. The crystal structure of the mononuclear boron compound was determined by single-crystal X-ray diffraction analysis. The photophysical properties of the boron compounds were investigated, and we found moderate fluorescence emission (compound 2 ΦF: 4.07% and compound 4 ΦF: 2.89%). We also observed that the mononuclear complex presented greater stability. Compound 4 showed interesting luminescent properties; in solid state, it exhibited an increase in fluorescence by mechanostimuli by changing to a bright red color, and also in solution, it showed a decrease in fluorescence intensity when oxygen and air were supplied to the solution.

Synthesis, Characterization, X-Ray Structure, and Conformation DFT Calculation of a Carbohydrazide Derivative

The synthesis and characterization of a new Carbonic dihydrazide, bis[2-(hydroxyimino)-1-methylpropylidene] is described. The compound was characterized by NMR (1H, 13C), high-resolution mass spectrometry and X-ray diffraction. We observed the ligand with anti-trans conformation in solid state and symmetric (C2) conformer in solution. The relative energies of the conformers were calculated, using the density functional theory (DFT) to determine their relative stability. Both the single-crystal and calculated structures indicate that the asymmetric conformer is the most stable conformer in the absence of solvent.Graphical Abstract

4-[(E)-(4-Fluoro-benzyl-idene)amino]-benzoic acid.

In the title compound, C14H10FNO2, the benzene rings make a dihedral angle of 57.50 (13)°, and the molecule has an E configuration about the C=N bond. In the crystal, molecules are linked via pairs of O—H⋯O hydrogen bonds, forming inversion dimers.