First Synthesis of Caerulomycin C

The first synthesis of caerulomycin C (1), an antibiotic produced by Streptomyces caeruleus, is reported. This molecule, which exhibits a 2,3,4,6-tetrasubstituted pyridine structure, was prepared from 3,4-dimethoxypyridine in a five-step sequence. The methodology involves metalation, transmetalation, aromatic cross-coupling, and halogen migration reactions.     

Iron carbonyl complexes of 2,3,5,6-tetrakis(methylene)-7-oxabicyclo[2.2.1]heptane. Crystal and molecular structure of (C10H10O)Fe(CO)3 and (C9H10CO)Fe2(CO)6

The reaction of 2,3,5,6-tetrakis(methylene)-7-oxabicyclo[2.2.1]heptane (I) with iron carbonyls in various solvents yields the (η⁴-1,3-diene)Fe(CO)₃ isomers (II: exo; III: endo) and the bimetallic isomers bis[(η⁴-1,3-diene)Fe(CO)₃] (IV: bis(exo); V: endo,exo). In weakly coordinating solvents, a parallel rearrangement of I occurs through CO bond cleavage of the allylic ether by Fe₂(CO)₉ yielding an unsaturated ketone (VI) bonded to two Fe(CO)₃ groups through a trimethylenemethane and a 1,3-diene system, respectively. The geometries of III and VI have been ascertained by X-ray crystal structure determinations.     

Synthesis of Cationic 2,4-Dimethylpenta-2,4-dienylruthenium Complexes. Crystal Structure of Carbonyl(η4-cyclohexa-1,3-diene)-(η5-2,4-dimethylpenta-2,4-dienyl)ruthenium Tetrafluoroborate

The complex [Ru(η⁵-C₇H₁₁)₂H]BF₄ (C₇H₁₁ = 2,4-dimethylpenta-2,4-dienyl) is highly reactive towards two- and six-electron ligands. e.g. giving with CO complex [RuCO(η⁴-C₇H₁₂)(η⁵-C₇H₁₁)]BF₄. The 2,4-dimethylpenta-1,3-diene ligand (C₇H₁₂) of the latter complex is readily displaced giving, e.g. with excess cyclohexa-1,3-diene (C₆H₈) complex [RuCO(η⁴-C₆H₈)(η⁵-C₇H₁₁)]BF₄. These reactions provide a convenient entry into monopentadienylruthenium chemistry.     

Synthesis,crystal and molecular structure of the 3:2 complex between europium nitrate and the A-isomer of dicyclohexyln-18-crown-6: Conformational study of the ligand

The crystal and molecular Structure of bis[dinitrato-(2,5,8,15,18,21-hexaoxatricyclo[20.4.0.0^9,14]hexa-consane)europium(III)]pentakis(nitrato) europiate(III) ([Eu(NO₃)₂·L_A]₂[Eu(NO₃)₅]) has been determined from single-crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P2₁/c (ITC No. 14): a = 13.614(3)Å, b = 21.697(4)Å, c = 22.591(5)Å, β = 107.15(2)°, Z = 4. The structure was refined to a final R value of 0.055 (R_w = 0.055). The asymmetric unit contains three independent ions with approximate C₂ symmetry: [Eu(NO₃)₅]^2? and two distinct [Eu(NO₃)₂.L_a]⁺ cations with the macrocyclic ligand in the cis-syn-cis-conformation (A-isomer). The Eu(III) ions are 10-coordinated with the following mean bond lengths: Eu? O(nitrate) = 2.46(3)Å in the anion and the two cations, Eu? O(ether) = 2.55(9)Å in both cations. For the uncomplexed A-and B-isomers, as well as for their complexes with various metal ions, a conformational analysis has been made on the six O-atoms of the ligand which can be considererd as a fluxional ring. In the presently reported europium complex cations, the oxygen-ring conformation is almost a perfect boat with the metal ions lying in the least-sqiares plane of the O-atoms (deviation: 0.02–0.05Å). The same conformation prevails in all the complexes containing the A-isomer(exception: dimethylthallium complex) and in most of the complexes with the B-isomer. For this isomer, a chair conformation is found in the uncomplexed ligand, in the sodium complex, and in the complex with dimethylthallium. The occurrence of these conformations is discussed with respect to the crystallographic symmetry of the complexes and the relative mean M? O and O? O distances.     

Prediction of solid solution formation in a family of diastereomeric salts. A molecular modeling study

The possibility of solid solution behavior of diastereomeric salts, containing multiple resolving agents of the same family (Dutch Resolution), is predicted by molecular modeling. Super-cells containing different ratios of resolving agents in the diastereomeric salt are constructed and optimized, and their lattice energy is computed. The energy difference between these "simulated solid solutions" and the native structures is related in an understandable fashion to the probability of solid solution formation. This procedure is applied to a family of diastereomeric salts of ephedrine and cyclic phosphoric acids, for which the ternary diagrams have been determined experimentally at 25 degrees C in ethanol. Good agreement between experimental and computational results indicates that this relatively simple and fast method could predict the stable character of solid solution behavior in binary systems.     

Crystal and Molecular Structure of Tricarbonyl-[(1R*, 4S*, 4aS*, 9aR*)-1,4-epoxy-2, 3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene]iron

The thermal cyclodimerization of 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene assisted by Fe₂ (CO)₉ gives the title complex 1 , a precursor for the synthesis of antitumoral anthracyclinones. The crystal structure of 1 has been determined by X-ray diffraction: a = 11.188 (1); c = 26.968 (3) Å; space group tetragonal, P4₁2₁2, Z = 8; R = 0.041; R_W = 0.033. The tricarbonyliron group is in the exo-position and the coordination polyhedron is tetragonal pyramidal. The NMR coupling constants are well-related to the observed dihedral angles between the non-aromatic protons and now give a reliable criterion for assigning the stereochemistry of the metal in d⁸-complexes of 2,3-dimethylidene-7-oxanorbornane derivatives.     

Remarkable diastereoselectivity in the addition of allylic and unsaturated diorganozinc reagents to beta-(N,N-dialkylamino)-aldehydes

1,3-Anti amino alcohols 5(a)-18(a) are obtained with high diastereoselectivity by use of diorganozinc reagents in additions to amino aldehydes 2a and 2b. The corresponding Grignard reagents exhibit low to modest diastereoselectivity. The highly diastereoselective zinc-based method makes available a wide range of 4,4-disubstituted cyclohexenone derivatives containing contiguous stereocenters.     

Pyranophane transannular diels-alder approach to (+)-chatancin: a biomimetic asymmetric total synthesis

An asymmetric total synthesis of (+)-chatancin was achieved via a transannular Diels-Alder (TADA) reaction of an in situ generated macrocyclic pyranophane pseudobase. The presented route constitutes the second of two proposed biosynthetic pathways that involves a TADA reaction. It links this diterpene biogenetically to the cembranoids. A set of TADA selection rules that rationalize the formation of (+)-chatancin from a dynamic equilibrium of four 2-hydroxy-2H-pyrane bicycles and their 16 potential TADA transition states are also outlined. Beyond the TADA reaction, highlights of the synthetic work include the assembly of a chiral acyclic macrocyclization substrate from (S)-citronellol and an efficient macrocyclization via a beta-ketosulfoxyde/enone Michael addition.     

Influence of solid solution formation on polarity: molecular modeling investigation of the system 4-chloro-4'-nitrostilbene/4,4'-dinitrostilbene

Growth-induced polarity formation in solid solutions composed of dipolar 4-chloro-4'-nitrostilbene molecules and nonpolar 4,4'-dinitrostilbene molecules was investigated by means of two molecular modeling procedures. Calculation of the mixing energy in the bulk structures predicted solid solution formation within the whole composition range. Computation of the interaction energies present at growing surfaces allowed the distribution coefficient as well as the fraction of dipoles in either the up or down orientation to be calculated by a mean-field model. Miscibility and polarity were found to vary for the faces (hkl) investigated, leading to crystals composed of sectors with different compositions and polarities. The present study highlights the fact that a solid solution crystal may not be a homogeneous entity and that surface effects arising during slow growth can have an impact on solid state properties.     

Synthesis of Carbon–Nitrogen–Phosphorous Materials with an Unprecedented High Amount of Phosphorous toward an Efficient Fire‐Retardant Material

Phosphorus incorporation into carbon can greatly modify its chemical, electronic, and thermal stability properties. To date this has been limited to low levels of phosphorus. Now a simple, large‐scale synthesis of carbon–nitrogen–phosphorus (CNP) materials is reported with tunable elemental composition, leading to excellent thermal stability to oxidation and fire‐retardant properties. The synthesis consists of using monomers that are liquid at high temperatures as the reaction precursors. The molten‐state stage leads to good monomer miscibility and enhanced reactivity at high temperatures and formation of CNP materials with up to 32 wt % phosphorus incorporation. The CNP composition and fire‐retardant properties can be tuned by modifying the starting monomers ratio and the final calcination temperature. The CNP materials demonstrate great resistance to oxidation and excellent fire‐retardant properties, with up to 90 % of the materials preserved upon heating to 800 °C in air.