The chemistry of vicinal polycarbonyl compounds

Iodosobenzene-mediated direct and efficient oxidation of β-dicarbonyls to vicinal tricarbonyls catalyzed by iron(iii) salts

The direct and efficient oxidation of β-dicarbonyls to vicinal tricarbonyl compounds has been achieved, which was mediated by PhIO and catalyzed by Fe(NO₃)₃·9H₂O under mild and environmentally friendly conditions.

A domino reaction of tetrahalo-7,7-dimethoxybicyclo[2.2.1]heptenyl alcohols leading to indenones and a de novo synthesis of ninhydrin derivatives

An acid mediated synthesis of indenones and a de novo synthesis of ninhydrin derivatives.

Photodissociation dynamics of enolic 1,2-cyclohexanedione at 266, 248, and 193 nm: mechanism and nascent state product distribution of OH

The photodissociation dynamics of 1,2-cyclohexanedione (CHD), which exists in enolic form in gas phase, is studied using pulsed laser photolysis (LP)-laser induced fluorescence (LIF) "pump-and-probe" technique at room temperature. The nascent state distribution of the OH radical, formed after initial photoexcitation of the molecule to it is (π, π*) and Rydberg states, is determined. The initial (π, π*) and Rydberg states are prepared by excitation with the fourth harmonic output of Nd:YAG (266 nm)/KrF (248 nm) and ArF (193 nm) lasers, respectively. The ro-vibrational distribution of the nascent OH photofragment is measured in collision-free conditions using LIF. The OH fragments are formed in the vibrationally cold state at all the above wavelengths of excitation but differ in rotational state distributions. At 266 nm photolysis, the rotational population of OH shows a curvature in Boltzmann plot, which is fairly described by two types of Boltzmann-like distributions characterized by rotational temperatures of 3100 ± 100 and 900 ± 80 K. However, at 248 nm photolysis, the rotational distribution is described by a single rotational temperature of 950 ± 80 K. The spin-orbit and Λ-doublets ratios of OH fragments formed in the dissociation process are also measured. The average translational energy in the center-of-mass coordinate, partitioned into the photofragment pairs of the OH formation channels, is determined to be 12.5 ± 3.0, 12.7 ± 3.0, and 12.0 ± 3.0 kcal/mol at 266, 248, and 193 nm excitation, respectively. The energy partitioning into various degrees of freedom of products is interpreted with the help of different models, namely, statistical, impulsive, and hybrid models. To understand the nature of the dissociative potential energy surface involved in the OH formation channel, detailed ab initio calculations are performed using configuration interaction-singles (CIS) method. It is proposed that at 266 nm photolysis, the OH fragment is formed from two different excited state structures, one with a strong H bonding, similar to that in the ground state, and another without effective H bonding, whereas, at 248 nm photodissociation, it seems that the OH formation occurs mainly from the excited state, which lacks effective H-bonding. At 193 nm excitation, the initially prepared population in the Rydberg state crosses over to a nearby σ* repulsive state along the C-O bond, from where the dissociation takes place. The exit barrier for the OH dissociation channel is estimated to be 14 kcal/mol. The existence of dynamical constraint due to strong hydrogen bond in the ground state is effectively present in the dissociation process at 266 and somewhat deficient at 248 nm photolysis.

Regioselective aliphatic carbon-carbon bond cleavage by a model system of relevance to iron-containing acireductone dioxygenase

Mononuclear Fe(II) complexes ([(6-Ph(2)TPA)Fe(PhC(O)C(R)C(O)Ph)]X (3-X: R = OH, X = ClO(4) or OTf; 4: R = H, X = ClO(4))) supported by the 6-Ph(2)TPA chelate ligand (6-Ph(2)TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-(2-pyridylmethyl)amine) and containing a β-diketonate ligand bound via a six-membered chelate ring have been synthesized. The complexes have all been characterized by (1)H NMR, UV-vis, and infrared spectroscopy and variably by elemental analysis, mass spectrometry, and X-ray crystallography. Treatment of dry CH(3)CN solutions of 3-OTf with O(2) leads to oxidative cleavage of the C(1)-C(2) and C(2)-C(3) bonds of the acireductone via a dioxygenase reaction, leading to formation of carbon monoxide and 2 equiv of benzoic acid as well as two other products not derived from dioxygenase reactivity: 2-oxo-2-phenylethylbenzoate and benzil. Treatment of CH(3)CN/H(2)O solutions of 3-X with O(2) leads to the formation of an additional product, benzoylformic acid, indicative of the operation of a new reaction pathway in which only the C(1)-C(2) bond is cleaved. Mechanistic studies show that the change in regioselectivity is due to the hydration of a vicinal triketone intermediate in the presence of both an iron center and water. This is the first structural and functional model of relevance to iron-containing acireductone dioxygenase (Fe-ARD'), an enzyme in the methionine salvage pathway that catalyzes the regiospecific oxidation of 1,2-dihydroxy-3-oxo-(S)-methylthiopentene to form 2-oxo-4-methylthiobutyrate. Importantly, this model system is found to control the regioselectivity of aliphatic carbon-carbon bond cleavage by changes involving an intermediate in the reaction pathway, rather than by the binding mode of the substrate, as had been proposed in studies of acireductone enzymes.

Divergent stereocontrol of acid catalyzed intramolecular aldol reactions of 2,3,7-triketoesters: synthesis of highly functionalized cyclopentanones

The intramolecular acid catalyzed aldol cyclization of 2,3,7-triketoesters formed from ζ-keto-α-diazo-β-ketoesters provides highly functionalized cyclopentanones with good diastereoselectivity in high overall yields via kinetically controlled and stereodivergent catalytic processes. Lewis acid catalysis gives high selectivity for the 1,2-anti tetrasubstituted cyclopentanones, whereas Brønsted acid catalysis produces the corresponding 1,2-syn diastereomer.

One-Pot Synthesis of α-Acyloxycarboxamidobarbiturates from Alloxans, Carboxylic Acids, and Isocyanides

A simple, efficient, and high yielding one-pot protocol for the synthesis of novel highly substituted α-acyloxycarbox-amidobarbiturates has been developed by a three-component reaction of alloxans, various carboxylic acids, and alkyl or aryl isocyanides in acetonitrile at room temperature.

An efficient methodology to substituted furans via oxidation of functionalized α-diazo-β-ketoacetates

DMDO oxidation of functionalized α-diazo-β-ketoacetates, formed by zinc triflate catalyzed Mukaiyama-aldol condensation of methyl diazoacetoacetate with aldehydes, occurred in quantitative yield to form dihydrofuranols that undergo acid catalyzed dehydration under mild conditions to generate 3-methoxyfuran-2-carboxylates in good yield.

Controlling the bonding and band gaps of solid carbon monoxide with pressure

We use a combination of a searching method and first-principles electronic structure calculations to predict novel structures of carbon monoxide (CO) which are energetically more stable than the known structures. The most stable forms of CO at zero pressure consist of metallic polycarbonyl chains with single and double bonds, rather than the familiar triply bonded insulating CO molecules. At pressures >2  GPa the most stable phases are semiconducting and insulating singly bonded three-dimensional framework and layered structures. We also find a molecular Pbcm structure which is more stable than the R3c structure proposed previously for the observed ϵ phase.

From furan to molecular stairs: syntheses, structural properties, and theoretical investigations of oligocyclic oligoacetals

The synthesis of oligocyclic oligoacetals using five-membered rings as repetitive unit is described. Furan was used as the starting material, which is converted by a three-step procedure consisting of twofold cyclopropanation, reduction, and oxidative ring enlargement into a tricyclic bis(enol ether). A repetition of this synthetic procedure leads to the formation of extended oligoacetal systems. Insights into the structures were gained by X-ray crystallographic investigations and revealed helical arrangements of the subunits in the solid-state. DFT (B3LYP) calculations have been carried out to elucidate the transition state of the ring enlargement and the flexibility of the annelated oligocyclic systems. Strain energies and topologies of potential cyclically condensed oligoacetals are predicted.

Multicomponent Tandem Synthesis of Oxospirobicyclic Butenolidobarbiturates

Novel oxospirobicyclic γ-butenolides containing barbiturate moiety have been synthesised by the Michael-addition of primary amines to dialkyl acetylenedicarboxylates followed by aldol-like reaction with alloxan derivatives, and then γ-lactonisation. Subsequent 1,4-addition of water and elimination of the amine group completes the sequence. This tandem reaction sequence represents a rapid and unprecedented route to the described biologically interesting molecules.

O2-dependent aliphatic carbon-carbon bond cleavage reactivity in a Ni(II) enolate complex having a hydrogen bond donor microenvironment; comparison with a hydrophobic analogue

A mononuclear Ni(II) complex having an acireductone type ligand, and supported by the bnpapa (N,N-bis((6-neopentylamino-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) ligand, [(bnpapa)Ni(PhC(O)C(OH)C(O)Ph)]ClO(4) (14), has been prepared and characterized by elemental analysis, (1)H NMR, FTIR, and UV-vis. To gain insight into the (1)H NMR features of 14, the air stable analogue complexes [(bnpapa)Ni(CH(3)C(O)CHC(O)CH(3))]ClO(4) (16) and [(bnpapa)Ni(ONHC(O)CH(3))]ClO(4) (17) were prepared and characterized by X-ray crystallography, (1)H NMR, FTIR, UV-vis, mass spectrometry, and solution conductivity measurements. Compounds 16 and 17 are 1:1 electrolyte species in CH(3)CN. (1)H and (2)H NMR studies of 14, 16, and 17 and deuterated analogues revealed that the complexes having six-membered chelate rings for the exogenous ligand (14 and 16) do not have a plane of symmetry within the solvated cation and thus exhibit more complicated (1)H NMR spectra. Compound 17, as well as other simple Ni(II) complexes of the bnpapa ligand (e.g., [(bnpapa)Ni(ClO(4))(CH(3)CN)]ClO(4) (18) and [(bnpapaNi)(2)(mu-Cl)(2)](ClO(4))(2) (19)), exhibit (1)H NMR spectra consistent with the presence of a plane of symmetry within the cation. Treatment of [(bnpapa)Ni(PhC(O)C(OH)C(O)Ph)]ClO(4) (14) with O(2) results in aliphatic carbon-carbon bond cleavage within the acireductone-type ligand and the formation of [(bnpapa)Ni(O(2)CPh)]ClO(4) (9), benzoic acid, benzil, and CO. Use of (18)O(2) in the reaction gives high levels of incorporation (>80%) of one labeled oxygen atom into 9 and benzoic acid. The product mixture and level of (18)O incorporation in this reaction is different than that exhibited by the analogue supported the hydrophobic 6-Ph(2)TPA ligand, [(6-Ph(2)TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO(4) (2). We propose that this difference is due to variations in the reactivity of bnpapa- and 6-Ph(2)TPA-ligated Ni(II) complexes with triketone and/or peroxide species produced in the reaction pathway.

Iron-mediated cleavage of C-C bonds in vicinal tricarbonyl compounds in water

Three of a kind: Vicinal tricarbonyl compounds undergo C-C cleavage mediated by ferric ions (see scheme). The observed cleavage of ninhydrin and dehydroascorbic acid has relevance for amino acid detection and the metabolism of vitamin C.