Reactivity Of Furan Research Articles

Equipping Coiled-Coil Peptide Dimers With Furan Warheads Reveals Novel Cross-Link Partners.

Using a coiled-coil peptide dimer as a model system to explore furan reactivity, we describe novel cross-link partners of furan warheads for site-specific cross-linking. We demonstrate that replacement of weak interhelical ionic contacts with a furan moiety and its potential cross-link partner affords covalently connected coiled-coil motifs upon furan activation. We describe for the first time the reaction of the activated furan warhead with cysteine and tyrosine, besides the previously reported lysine, thus enhancing the versatility of the furan cross-link methodology by the possibility to target different amino acids. The present in vitro validation of “furan-armed” α-helices provides further grounds for exploiting furan technology in the development of furan-modified ligands/proteins to target proteins in a covalent way through various amino acid side chains.

Reactions of Three Lactones with Cl, OD, and O3: Atmospheric Impact and Trends in Furan Reactivity

Lactones, cyclic esters of hydroxycarboxylic acids, are interesting biofuel candidates as they can be made from cellulosic biomass and have favorable physical and chemical properties for distribution and use. The reactions of γ-valerolactone (GVL), γ-crotonolactone (2(5H)-F), and α-methyl-γ-crotonolactone (3M-2(5H)-F) with Cl, OD, and O3 were investigated in a static chamber at 700 Torr and 298 ± 2 K. The relative rate method was used to determine kGVL+Cl = (4.56 ± 0.51) × 10-11, kGVL+OD = (2.94 ± 0.41) × 10-11, k2(5H)-F+Cl = (2.94 ± 0.41) × 10-11, k2(5H)-F+OD = (4.06 ± 0.073) × 10-12, k3M-2(5H)-F+Cl = (16.1 ± 1.8) × 10-11, and k3M-2(5H)-F+OD = (12.6 ± 0.52) × 10-12, all rate coefficients in units of cm3 molecule-1 s-1. An absolute rate method was used to determine k2(5H)-F+O3 = (6.73 ± 0.18) × 10-20 and k3M-2(5H)-F+O3 = (5.42 ± 1.23) × 10-19 in units of cm3 molecule-1 s-1. Products were identified for reactions of the lactones with Cl. In the presence of O2 the products are formic acid (HCOOH), formyl chloride (CHClO), and phosgene (CCl2O), and also maleic anhydride (C2H2(CO)2O) for 2(5H)-F. In addition both reactions produced a number of unidentified products that likely belong to molecules with the ring-structure intact. A review of literature data for reactions of other furans show that the reactivity of the lactones are generally lower compared to that of corresponding compounds without the carbonyl group.

Synthesis, characterization, and reactivity of furan- and thiophene-functionalized bis(N-heterocyclic carbene) complexes of iron(II).

The synthesis of iron(II) complexes bearing new heteroatom-functionalized methylene-bridged bis(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (2a) and tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenethiophene)methane]iron(II) hexafluorophosphate (2b) were obtained by aminolysis of [Fe{N(SiMe3)2}2(THF)] with furan- and thiophene-functionalized bis(imidazolium) salts 1a and 1b in acetonitrile. The SC-XRD structures of 2a and 2b show coordination of the bis(carbene) ligand in a bidentate fashion instead of a possible tetradentate coordination. The four other coordination sites of these distorted octahedral complexes are occupied by acetonitrile ligands. Crystallization of 2a in an acetone solution by the slow diffusion of Et2O led to the formation of cis-diacetonitriledi[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (3a) with two bis(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds 2a and 2b are the first reported iron(II) carbene complexes with four coordination sites occupied by solvent molecules, and it was demonstrated that those solvent ligands can undergo ligand-exchange reactions.

Synthesis of a highly functionalized core of verrillin.

An efficient stereoselective synthesis of furanoverrillin (5), a highly functionalized core of verrillin (1), is reported. The synthetic strategy is based on constructing bicyclic lactone 17 prior to the 10-membered ring macrocyclization. The effect of the C4 methyl group on the furan reactivity is also discussed.

ChemInform Abstract: Microwave‐Assisted Furan Cycloadditions: Quantum‐Chemical Reactivity Assessment

AbstractReview: 40 refs.

A comparison of the benzo[b]furan and benzo[c]furan reactivity in diels-alder reactions through an AM1 computational study

The aromaticity of benzo[c]furan was evaluated based on the uniformity of the CC bond distances and their deviation from the ideal aromatic CC bond distance. The AM1 computed values were compared to those of furan and benzo[b]furan. The goal was to determine the relative stability and reactivity of benzo[b]furan. The reactivity of benzo[c]furan as a diene for the Diels-Alder reaction was estimated through its HOMO energy and activation barriers using several dienophiles.

Chemisorption and reactivity of furan on Pd{111}

XPS, HREELS, ARUPS and Δø data show that furan chemisorbs non-dissociatively on Pd{111} at 175 K, the molecular plane being significantly tilted with respect to the surface normal. Bonding involves both the oxygen lone pair and significant π interaction with the substrate. The degree of decomposition that accompanies molecular desorption is a strong function of coverage: ∼40% of the adsorbate desorbs molecularly from the saturated monolayer. Decomposition occurs via decarbonylation to yield CO a and H a followed by desorption rate limited loss of H 2 and CO. It seems probable that an adsorbed C 3H 3 species formed during this process undergoes subsequent stepwise dehydrogenation ultimately yielding H 2 and C a.

Allene and fluoroallenes as dienophiles in Diels–Alder reactions: an AM1 and PM3 study

Transition structures and energetics of Diels–Alder reactions of allene with cyclopentadiene and hexachlorocyclopentadiene, and fluoroallenes with cyclopentadiene and furan have been investigated using semiempirical MO methods at AM1 and PM3 levels. Allene and fluoroallenes react through an asynchronous transition structure in which the terminal carbon atom involved in the reaction pyramidalizes and the central carbon atom triangulates and this deformation accounts for almost half the reaction barrier. Allene is found to be a less reactive dienophile compared to ethylene, contrary to expectations, and its reactivity enhances with fluorine substitution up to 1,1-difluoroallene and declines on further substitution of fluorine. Tetrachloroallene is found to be less reactive than allene itself. The reactivity of furan in such cumulene reactions is found to be almost the same as that of cyclopentadiene. While PM3 predictions in certain cases are not reliable AM1 reaction barriers explain reasonably the reactivities and stereochemical preferences of the above reactions.

Organic reactions with rhodium carbonyl cluster catalysts

Rhodium carbonyl clusters have been found to catalyze two types of reactions: (1) Carbon-hydrogen bond activation of aromatic compounds and (2) Cross-hydrocarbonylation of acetylenes and olefins.(1) Under pressure of carbon monoxide (20 to 30 atm) and at higher temperatures (180 to 220 °C), rhodium carbonyl clusters Rh4(CO)12 and Rh6(CO)16 catalyze the addition of a C-H bond of benzene to unsaturated compounds such as diphenylketene, isocyanates and acetylenes to give phenylated compounds such as diphenylacetophenone, benzamides and phenylated olefins, respectively. Five-membered heterocycles such as furan, thiophene, and AT-methylpyrrole also react similarly with diphenylacetylene to give 2-furyl-, 2-thienyl- and 2-(N-methylpyrrolyl)-olefins, respectively.Among these, the reactivity of furan is the highest and is about 200 times that of benzene. In the reactions of arene with olefins, aryl-substituted olefins are obtained instead of simple addition products. For example, the reaction of benzene with ethylene gives styrene directly. The hydrogen generated in these reactions is used for the hydrocarbonylation or the hydrogenation of the starting olefins, yielding ketones or saturated compounds. The reaction of furan with olefins gives furyl olefins similarly. In the reactions of secondary amines such as indole, carbazole, and diphenylamine, the N-H bond participates in preference to the C-H bond, giving Nvinyl compounds. Regioselectivities in the reactions of substituted benzenes suggest the protophilic nature in the stage of C-H bond activation. The following mechanism is proposed: (1) initial oxidative addition of an aromatic C-H bond to the rhodium catalyst to give aryl- and hydride-rhodium species, (2) insertion of unsaturated compounds into the aryl-rhodium bond, and (3) reductive elimination with the hydride or β-hydrogen elimination affording the corresponding aryl-substituted compounds.(2) The cross-hydrocarbonylations of acetylenes and ethylene with carbon monoxide are found to give 5-ethyl-2(5H)-furanones when hydrogendonating solvents are used, and to give α, β-unsaturated ethyl ketones when molecular hydrogen is introduced into the reaction system. Since it is consistent with the regioselectivity in the reactions of unsymmetrical acetylenes, a β-acylvinyl rhodium intermediate is proposed as a common key intermediate for these two products. The convenient syntheses of 5-alkoxy2(5H)-furanones from acetylenes, carbon monoxide and alcohols are attained by adding a basic alkali metal salt such as NaOAc or Na2CO3 as a cocatalyst.