Halide Anion Triggered Reactions of Michael Acceptors with Tropylium Ion

Tropylium bromide undergoes noncatalyzed, regioselective additions to a large variety of Michael acceptors. In this way, acrylic esters are converted into β-bromo-α-cycloheptatrienylpropionic esters. The reactions are interpreted as nucleophilic attack of bromide ions at the electron-deficient olefins and the approach of the tropylium ion to the incipient carbanion. Quantum chemical calculations were performed to elucidate the analogy to the amine- or phosphine-catalyzed Rauhut–Currier reactions. Subsequent synthetic transformations of the bromo-cycloheptatrienylated adducts are reported.     

Halide Anion Triggered Reactions of Michael Acceptors with Tropylium Ion

Tropylium bromide undergoes noncatalyzed, regioselective additions to a large variety of Michael acceptors. In this way, acrylic esters are converted into β‐bromo‐α‐cycloheptatrienylpropionic esters. The reactions are interpreted as nucleophilic attack of bromide ions at the electron‐deficient olefins and the approach of the tropylium ion to the incipient carbanion. Quantum chemical calculations were performed to elucidate the analogy to the amine‐ or phosphine‐catalyzed Rauhut–Currier reactions. Subsequent synthetic transformations of the bromo‐cycloheptatrienylated adducts are reported.     

Synthesis of 5-oxo-5H-chromeno[3,4-c]pyridine-1-carbonitriles and features of their NMR spectra

Two different methods leading to 5-oxo-5H-chromeno[3,4-c]pyridine-1-carbonitriles were investigated. Reactions of 3-aminocrotonirile with substituted salicylaldehydes provided 5-oxo-5H-chromeno[3,4-c]pyridine-1-carbonitriles with the same substituent on positions 2 and 4 of the system. The reaction of 3-aminocrotonirile with variety of substituted 3-acetylcoumarins lead to 5-oxo-5H-chromeno[3,4-c]pyridine-1-carbonitriles with different substituents on positions 2 and 4. The structures of the products were confirmed by spectroscopic methods. The presence of nitrile moiety in the structures with fixed geometry caused the highly downfield shift of the aromatic proton at position 10 in ¹H NMR spectrum. The electronic factor of the substituents caused variation of this downfield shift.     

First synthesis of 4-(arylsulfonyl)phenols by regioselective [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with 2-arylsulfonyl-3-ethoxy-2-en-1-ones

The formal [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with readily available 2-arylsulfonyl-3-ethoxy-2-en-1-ones resulted in regioselective formation of 4-(arylsulfonyl)phenols.     

Regioselective synthesis of functionalized 4-nitro- and 4-amino-phenols based on formal [3+3] cyclocondensations of 3-ethoxy-2-nitro-2-en-1-ones with 1,3-bis(silyloxy)-1,3-butadienes

Functionalized 4-nitro- and 4-aminophenols were regioselectively prepared based on [3+3] cyclizations of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-ethoxy-2-nitro-2-en-1-ones.     

6-Chlorothieno[2,3-<Emphasis Type="Italic">e</Emphasis>]-1,4,2-dithiazine-3(2<Emphasis Type="Italic">H</Emphasis>)-thione-1,1-dioxide,Ammonium Salt Sesquihydrate: Synthesis,Crystal Structure and Density Functional Calculations

Abstract  

The title compound crystallizes in the monoclinic space group C2/c space group, with unit cell dimensions of a = 15.6684(3) ?, b = 7.3974(2) ?, c = 21.2669(5) ?; β = 106.7770(10)° (Z = 8). In the title compound, NH₄ ⁺·C₅HClNO₂S₄ ^–·1.5 H₂O, the 1,4,2-dithiazine ring adopts a distorted half-chair conformation. The structure displays several cooperative intermolecular N/O–H···N/O/S hydrogen-bonding interactions, giving rise to a two-dimensional layers packing motif. The layers are built up from seven component entities formed via extensive intermolecular N/O–H···N/O/S hydrogen bonds involving 6-chlorothieno[2,3-e]-1,4,2-dithiazine-3(2H)-thione-1,1-dioxide anions, ammonium cations and water molecules. The geometry of the title compound was fully optimized using a Density functional B3LYP/6-31G(d) and B3LYP/6-31+G(d) methods and the results were consistent with experimental values. The binding energy and associated basis set superposition as well as the thermodynamic quantities were calculated.     

Regioselective synthesis of amino- and nitroarenes based on [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes

Functionalized amino- and nitro-substituted biaryls and dibenzo[b,d]pyrid-6-ones (6(5H)-phenanthridinones) were prepared by [3+3]cyclocondensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with nitro-substituted 1-aryl-1-silyloxy-1-en-3-ones and subsequent hydrogenation. 4-Nitro- and 4-aminophenols were prepared based on formal [3+3] cyclizations of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-ethoxy-2-nitro-2-en-1-ones.     

Solid-phase synthesis of the cyclic peptide portion of chlorofusin, an inhibitor of p53-MDM2 interactions

The first solid-phase synthesis of the chlorofusin peptide is described. The synthesis involved side-chain immobilization of N(alpha)-Fmoc-Asp-ODmab. Synthesis of the linear peptide, initially incorporating racemic Ade8 and unsubstituted ornithine in place of the chromophore-bearing residue, was followed by cyclization on resin and peptide release to give a mixture of diastereomers. Resynthesis identified (by HPLC) the second isomer as analogous to the natural product. Initial biological assays, using an immunofluorescence method, suggest that the compounds are not cytotoxic but do not inhibit the p53/mdm2 interaction. [structure: see text]     

Guest‐, Light‐ and Thermally‐Modulated Spin Crossover in [FeII2] Supramolecular Helicates

A new bis(pyrazolylpyridine) ligand (H₂L) has been prepared to form functional [Fe₂(H₂L)₃]⁴⁺ metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe₂(H₂L)₃]X(PF₆)₂?xCH₃OH ( 1 , x=5.7 and X=Cl; 2 , x=4 and X=Br), X@[Fe₂(H₂L)₃]X(PF₆)₂?yCH₃OH?H₂O ( 1 a , y=3 and X=Cl; 2 a , y=1 and X=Br) and X@[Fe₂(H₂L)₃](I₃)₂?3 Et₂O ( 1 b , X=Cl; 2 b , X=Br). Their structure and functional properties are described in detail by single‐crystal X‐ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2 , respectively, by a single‐crystal‐to‐single‐crystal mechanism. The three possible magnetic states, [LS–LS], [LS–HS], and [HS–HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe^II centers. The nature of the guest (Cl^? vs. Br^?) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS–HS] or [HS–HS] states are generated through irradiation. All helicates (X@[Fe₂(H₂L)₃])³⁺ persist in solution.     

Combining valproate and bipyridyl ligands to construct a 0D core‐shell Zn5(μ3‐OH)2 cluster and a 2D layered coordination network with a [Zn3(μ3‐OH)]2 SBU

Starting from the proposed zinc carboxylate cluster tetrakis(μ‐2‐propylpentanoato)dizinc(II), Zn₂(μ₂‐valp)₄ ( I ), of valproic acid, a branched short‐chain fatty acid, and bipyridine ligands, two new mixed‐ligand coordination compounds, namely, bis(2,2′‐bipyridine)di‐μ₃‐hydroxido‐hexakis(μ‐2‐propylpentanoato)bis(2‐propylpentanoato)pentazinc(II), [Zn₅(C₈H₁₅O₂)₈(OH)₂(C₁₀H₈N₂)₂] ( II ), and poly[[bis(μ‐4,4′‐bipyridine)di‐μ₃‐hydroxido‐octakis(μ‐2‐propylpentanoato)bis(2‐propylpentanoato)hexazinc(II)] dimethylformamide disolvate], {[Zn₆(C₈H₁₅O₂)₁₀(OH)₂(C₁₀H₈N₂)₂]·2C₃H₇NO}_n ( III ), were synthesized. Compound II is a core‐shell‐type zero‐dimensional discrete Zn₅(μ₃‐OH)₂ metal–organic cluster with Zn ions in double‐triangle arrangements that share one Zn ion coincident with an inversion centre. The cluster contains three crystallographically non‐equivalent Zn ions exhibiting three different coordination geometries (tetrahedral, square pyramidal and octahedral). The cluster cores are well separated and embedded in a protective shell of the aliphatic branched short chains of valproate. As a result, there is no specific interaction between the discrete clusters. Conversely, compound III , a 2D layered coordination network with a secondary building unit (SBU), is formed by Zn₆(μ₃‐OH)₂ clusters exhibiting a chair‐like hexagonal arrangement. This SBU is formed from two Zn₃(μ₃‐OH) trimers related by inversion symmetry and connected by two syn–anti bridging carboxylate groups. Each SBU is connected by four 4,4′‐bipyridine ligands producing a 6³‐hcb net topology. 2D coordination layers are sandwiched within layers of dimethylformamide molecules that do not interact strongly with the network due to the hydrophobic protection provided by the valproate ligands.