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Lignin is an abundant natural feedstock that offers great potential as a renewable substitute for fossil-based resources. Its polyaromatic structure and unique properties have attracted significant research efforts. The advantages of an enzymatic over chemical or thermal approach to construct or deconstruct lignins are that it operates in mild conditions, requires less energy, and usually uses non-toxic chemicals. Laccase is a widely investigated oxidative enzyme that can catalyze the polymerization and depolymerization of lignin. Its dual nature causes a challenge in controlling the overall direction of lignin-laccase catalysis. In this Review, the factors that affect laccase-catalyzed lignin polymerization were summarized, evaluated, and compared to identify key features that favor lignin polymerization. In addition, a critical assessment of the conditions that enable production of novel lignin hybrids via laccase-catalyzed grafting was presented. To assess the industrial relevance of laccase-assisted lignin valorization, patented applications were surveyed and industrial challenges and opportunities were analyzed. Finally, our perspective in realizing the full potential of laccase in building lignin-based materials for advanced applications was deduced from analysis of the limitations governing laccase-assisted lignin polymerization and grafting.

Chemical functionalisation is one of the most active areas of graphene research, motivated by fundamental science, the opportunities to adjust or supplement intrinsic properties, and the need to assemble materials for a broad array of applications. Historically, the primary consideration has been the degree of functionalisation but there is growing interest in understanding how and where modification occurs. Reactions may proceed preferentially at edges, defects, or on graphitic faces; they may be correlated, uncorrelated, or anti-correlated with previously grafted sites. A detailed collation of existing literature data indicates that steric effects play a strong role in limiting the extent of reaction. However, the pattern of functionalisation may have important effects on the resulting properties. This article addresses the unifying principles of current graphene functionalisation technologies, with emphasis on understanding and controlling the locus of functionalisation.

International audience; In this paper, we show that trans effects in octahedral complexes can primarily be related to differences in the ability, for a given ligand, to cede electron density to the metal cation under the influence of the ligand at the trans position. Using tools from conceptual DFT or from related paradigms, we highlight these effects on a set of representative examples and further provide the basis for a computational trans effect scale. This quantification notably retrieves the experimental trans orienting series.

International audience; In this letter, we propose a straightforward evaluation of atomic electronegativities within the framework of Bader's atoms-in-molecules theory, based on the basin decomposition of the molecular electronic chemical potential derived from the Kohn-Sham equations through the non-interacting kinetic energy. The use of such atomic descriptors for reactivity purposes is then illustrated on the prediction of the electrophilicity of carbon atoms in organic reagents.

Translating local electro/nucleophilicities into the language of reactive sites is an appealing theoretical challenge that could be conducive to strengthen the collaborative dialogue between experimentalists and quantum chemists. The usual schemes for such condensation, relying on atomic charges, may however lead to important information loss, due to a sometimes inappropriate averaging of the reactivity anisotropy. In this article, we present instead an approach based on the dual descriptor Δf, which aims at partitioning real space into nonoverlapping reactive domains that feature a constant Δf sign. This strategy enables not only to identify the nucleo/electrophilic regions inside a molecule but also to quantify meaningful properties (mean value, volume, electron population…). Its interest is then illustrated on two specific chemical problems: the measure of σ-holes in the context of halogen bonds, and of the electrophilicity of organic carbocations, casting the light on the versatility of this method. © 2015 Wiley Periodicals, Inc.

Michael addition (MA) is one of the most well studied chemical transformation in synthetic chemistry. Here, we report the synthesis and crystal structures of a library of 3d/4f coordination clusters (CCs) formulated as [ZnII 2YIII 2L4(solv)X(Z)Y] and study their catalytic properties toward the MA of nitrostyrenes with barbituric acid derivatives. Each CC presents two borderline hard/soft Lewis acidic ZnII centers and two hard Lewis acidic YIII centers in a defect dicubane topology that brings the two different metals into a proximity of ∼3.3 Å. Density functional theory computational studies suggest that these tetrametallic CCs dissociate in solution to give two catalytically active dimers, each containing one 3d and one 4f metal that act cooperatively. The mechanism of catalysis has been corroborated via NMR, electron paramagnetic resonance, and UV-vis. The present work demonstrates for the first time the successful use of 3d/4f CCs as efficient and high diastereoselective catalysts in MA reactions.

In this work, the dual-descriptor is studied in matrix form f(2) (r, r') and both coordinates condensed to atoms, resulting in atomic and diatomic (or where applicable, bond) condensed single values. This double partitioning method of the dual-descriptor matrix is proposed within the Hirshfeld-I atoms-in-molecule framework although it is easily extended to other atoms-in-molecules methods. Diagonalizing the resulting atomic and bond dual-descriptor matrices gives eigenvalues and eigenvectors describing the reactivity of atoms and bonds. The dual-descriptor function is the diagonal element of the underlying matrix. The extra information contained in the atom and bond resolution is highlighted and the effect of choosing either the fragment of molecular response or response of molecular fragment approach is quantified., Facultad de Ciencias Exactas, Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Pierre Mignon and Philippe Chaumont are acknowledged for helpful discussions.; International audience; A joint experimental and theoretical study has been carried out on reversible addition-fragmentation chain transfer polymerisation (RAFT). We have performed density functional theory calculations at the (Perdew-Burke-Ernzerhof) PBE/triple zeta plus polarisation level to analyse the RAFT mechanisms corresponding to these compounds. Global and local reactivity indices have been calculated to investigate the effect of the addition of methyl, cyanomethyl and styryl radicals on the double bond C=S of thionoester compounds producing an adduct radical. This mechanism is shown to be difficult when the cyanomethyl is used contrarily to the methyl and styryl radicals, in agreement with experimental results. The activation barrier of fragmentation of adduct radicals does not correlate well with the length of fragmented bond (O-C-alpha). The bond topological analysis of radical adduct predicts that the distance between the oxygen and a critical point (O-CP) in the fragment bond is a good parameter to estimate the activation energy of the fragmentation mechanism. It is shown that the nature of the free radicals is more selective than that of the thionoester compounds. With an overall large agreement with experiments, these theoretical results afford an explanation of the efficiency for the RAFT mechanism.

In this paper, we show that the ambiphilic properties of some organic ligands in organometallic complexes may be retrieved readily from simple calculations in the framework of conceptual density functional theory (C-DFT): namely, the dual descriptor (DD) and the molecular electrostatic potential (MEP) of the ligands afford a rather straightforward interpretation of experimental trends such as the bonding geometry and the electronic properties of complexes in terms of σ-, π- and back-bonding. The studied ligands were chosen to be representative of the wide variety organometallic chemistry offers, ranging from neutral to charged systems and from diatomic to polyatomic molecules. The present approach is general since all relevant parameters are retrieved from the electron density, obtained either from a DFT or post-Hartree-Fock calculation. It is believed to be helpful for organometallic chemists, since it allows a deep understanding and may be used as a predictive tool of the coordinating properties of ligands.

Bond Fukui functions and matrices are introduced for ab initio levels of theory using a Mulliken atoms in molecules model. It is shown how these indices may be obtained from first-order density matrix derivatives without need for going to second-order density matrices as in a previous work. The importance of taking into account the nonorthogonality of the basis in ab initio calculations is shown, contrasting the present results with previous work based on Huckel theory. It is shown how the extension of Fukui functions to Fukui matrices allows getting more insight into the nature of bond Fukui functions. All presently introduced indices respect the necessary normalization conditions and include the classical single atom condensed Fukui functions. © 2013 Wiley Periodicals, Inc.

We describe the use of conceptual DFT based quantum chemical molecular fields for three-dimensional quantitative structure–activity relations (3D QSARs) and compare this new approach with the use of the default molecular property fields. The use of the new molecular fields in 3D QSAR is investigated by an application in the field of drug discovery, in which the antituberculotic activity of salicylamide derivatives is investigated. It is shown that conceptual DFT molecular fields have an added value to the default considered CoMFA fields.

We present explicit formulas for arbitrary-order derivatives of the energy, grand potential, electron density, and higher-order response functions with respect to the number of electrons, and the chemical potential for any smooth and differentiable model of the energy versus the number of electrons. The resulting expressions for global reactivity descriptors (hyperhardnesses and hypersoftnesses), local reactivity descriptors (hyperFukui functions and local hypersoftnesses), and nonlocal response functions are easy to evaluate computationally. Specifically, the explicit formulas for global/local/nonlocal hypersoftnesses of arbitrary order are derived using Bell polynomials. Explicit expressions for global and local hypersoftness indicators up to fifth order are presented.

International audience; By means of the Spin-Polarized Conceptual Density Functional Theory (SP-CDFT), three 2,6-bis(imino) pyridine catalysts based on iron(II), used for polymerization of ethylene, were studied. The catalysts differed by the substituent group, bearing either -H, -NO2 or -OCH3. To date, catalytic activity, a purely experimental parameter measuring the mass of polyethylene produced per millimole of iron per time and pressure unit at a fixed temperature, has not been explained in terms of local hyper-softness. The latter is a purely theoretical parameter designed for quantifying electronic effects; it is measured using the metal atom responsible for the coordination process with the monomer (ethylene). Because steric effects are not relevant in these kinds of catalysts and only electronic effects drive the catalytic process, an interesting link is found between catalytic activity and the local hyper-softness condensed on the iron atom by means of four functionals (B3LYP, BP86, B97D, and VSXC). This work demonstrates that the use of local hyper-softness, predicted by the SP-CDFT, is a suitable parameter for explaining order relationships among catalytic activity values, thus quantifying the electronic influence of the substituent group inducing this difference; the use of only net electric charges does not lead to clear conclusions. This finding can aid in estimating catalytic activities leading to a more rational design of new catalysts via computational chemistry.

Radiative transitions between the three lowest-lying electronic states of molecular oxygen have long provided a model to study how collision-dependent perturbations influence forbidden processes. In an isolated oxygen molecule, transitions between the O-2(X-3 Sigma(-)(g)), O-2(a(1)Delta(g), and O-2(b(1)Sigma(+)(g)) states are forbidden as electric-dipole processes. For oxygen dissolved in organic solvents, the probabilities of radiative transitions between these states increase appreciably. Attempts to interpret solvent-dependent changes in the radiative rate constants have principally relied on O-2(b(1)Sigma(+)(g)) and O-2(a(1)Delta(g)) emission experiments. However, the dominant nonradiative deactivation channels of O-2(b(1)Sigma(+)(g)) make it difficult to quantify solvent effects on the O-2(b(1)Sigma(+)(g)) -> O-2(a(1)Delta(g)) radiative process. Thus, an appreciable amount of important information has heretofore not been available. In the present study, we examined the effect of 17 common organic solvents on the O-2(a(1)Delta(g)) -> O-2(b(1)Sigma(+)(g)) absorption transition at similar to 5200 cm(-1) (i.e., similar to 1925 nm). The solvent-dependent absorption coefficients at the band maximum, em, range from 5 to 50 M-1 cm(-1) and correlate reasonably well with the solvent refractive index; emax is largest in solvents with the largest refractive index. This observation is consistent with a model in which oxygen is perturbed to a greater extent by solvents with a large electronic polarizability. Through the Strickler-Berg equation, we also used these absorption data to obtain the radiative rate constant for the O-2(b(1)Sigma(+)(g)) -> O-2(a(1)Delta(g)) transition, and the results are consistent with a model in which the O-2(a(1)Delta(g)) -> O-2(X-3 Sigma(-)(g)) transition is said to steal intensity from the O-2(b(1)Sigma(+)(g)) -> O-2(a(1)Delta(g)) transition.

The nature of rate-retarding effects of cationic micelles on the water-catalyzed hydrolyses of a series of para-substituted 1-benzoyl-1,2,4-triazoles (1a-f) and 1-benzoyl-3-phenyl-1,2,4-triazole (2) has been studied using kinetic methods. A comparison is drawn between medium effects in the micellar Stern region and in model solutions for the micellar Stern region. Simple model solutions involving concentrated aqueous solutions of a small ionic molecule resembling the surfactant headgroup, as reported before,1 were improved. New model solutions for alkyltrimethylammonium bromide micelles contain both tetramethylammonium bromide (TMAB), mimicking micellar headgroups, and 1-propanol, mimicking hydrophobic tails. The rate-retarding effect of micelles on the hydrolysis of 1a-f and 2 is caused by the high concentration of headgroups as well as by hydrophobic tails in the Stern region where 1a-f and 2 bind to the micelle. Individual contributions of these interactions are quantified. Rate-retarding effects found for different probes, with different sensitivities for interactions as they occur when the probe binds to the micellar Stern region, as well as the micellar Stern region’s micropolarity as reported by the ET(30) probe, are satisfactorily reproduced by new model solutions containing both TMAB and 1-propanol.

The nature of rate-retarding effects of cationic micelles on the water-catalyzed hydrolyses of a series of para-substituted 1-benzoyl-1,2,4-triazoles (1a-f) and 1-benzoyl-3-phenyl-1,2,4-triazole (2) has been studied using kinetic methods. A comparison is drawn between medium effects in the micellar Stern region and in model solutions for the micellar Stern region. Simple model solutions involving concentrated aqueous solutions of a small ionic molecule resembling the surfactant headgroup, as reported before,1 were improved. New model solutions for alkyltrimethylammonium bromide micelles contain both tetramethylammonium bromide (TMAB), mimicking micellar headgroups, and 1-propanol, mimicking hydrophobic tails. The rate-retarding effect of micelles on the hydrolysis of 1a-f and 2 is caused by the high concentration of headgroups as well as by hydrophobic tails in the Stern region where 1a-f and 2 bind to the micelle. Individual contributions of these interactions are quantified. Rate-retarding effects found for different probes, with different sensitivities for interactions as they occur when the probe binds to the micellar Stern region, as well as the micellar Stern region’s micropolarity as reported by the ET(30) probe, are satisfactorily reproduced by new model solutions containing both TMAB and 1-propanol.

International audience; The 5-methylcytosine derivative 5-hydroxymethylcytosine (5hmCyt), which is generated via enzymatic oxidation, is sometimes referred to as the sixth nucleobase due to its widespread presence in the DNA of brain and embryonic stem cells. In this study, we used density functional based methods and reactivity indices from conceptual DFT to explore the mechanism and key features of the hydrolytic deamination of 5hmCyt. The data obtained are used to compare and contrast this deamination reaction with those of other cytosine derivatives. The deamination process for 5hmCyt is similar to the corresponding processes for other unsaturated derivatives in that the amino form is the reactive one and water addition is the rate-limiting step. However, several differences due to the rotameric asymmetry of the current system are also noted.

International audience; Intra-molecular Diels-Alder (IMDA) reactions of tethered trienes can furnish two distinct diastereoisomeric products, the cis (i.e., endo) stereoisomer and the trans (i.e., exo) stereoisomer. Experimental evidence shows a quite high cis stereoselectivity for 10-link compounds (cis/trans = 70: 30), while 11- and 12-links compounds exhibit no particular selectivity. DFT (B3LYP/6-31G*) computations provide useful insights into the origins of this amazing stereo-selectivity. The cyclization path towards trans stereo-isomer is always thermodynamically favored, whatever the size of the system. The high cis stereo-selectivity displayed by the 10-link system is kinetically controlled by a tug-of-war between ring strain and electronic effects in the transition structure. The dual descriptor of chemical reactivity, a conceptual DFT based descriptor designed to delineate electronic effects, has been used to unravel the stabilizing processes that take place at the TSs.

This article explores the extent to which insights gleaned from detailed studies of molecular photodissociations in the gas phase (i.e. under isolated molecule conditions) can inform our understanding of the corresponding photofragmentation processes in solution. Systems selected for comparison include a thiophenol (p-methylthiophenol), a thioanisole (p-methylthioanisole) and phenol, in vacuum and in cyclohexane solution. UV excitation in the gas phase results in RX-Y (X = O, S; Y = H, CH3) bond fission in all cases, but over timescales that vary by similar to 4 orders of magnitude - all of which behaviours can be rationalised on the basis of the relevant bound and dissociative excited state potential energy surfaces (PESs) accessed by UV photoexcitation, and of the conical intersections that facilitate radiationless transfer between these PESs. Time-resolved UV pump-broadband UV/visible probe and/or UV pump-broadband IR probe studies of the corresponding systems in cyclohexane solution reveal additional processes that are unique to the condensed phase. Thus, for example, the data clearly reveal evidence of (i) vibrational relaxation of the photoexcited molecules prior to their dissociation and of the radical fragments formed upon X-Y bond fission, and (ii) geminate recombination of the RX and Y products (leading to reformation of the ground state parent and/or isomeric adducts). Nonetheless, the data also show that, in each case, the characteristics (and the timescale) of the initial bond fission process that occurs under isolated molecule conditions are barely changed by the presence of a weakly interacting solvent like cyclohexane. These condensed phase studies are then extended to an ether analogue of phenol (allyl phenyl ether), wherein UV photo-induced RO-allyl bond fission constitutes the first step of a photo-Claisen rearrangement.

Halogen bonds between the trifluoromethyl halides CF3Cl, CF3Br and CF3I, and dimethyl ether, dimethyl sulfide, trimethylamine and trimethyl phosphine were investigated using Pearson's hard and soft acids and bases (HSAB) concept with conceptual DFT reactivity indices, the Ziegler-Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework and the non-covalent interaction (NCI) index. It is found that the relative importance of electrostatic and orbital (charge transfer) interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. Dual-descriptor plots indicate an orbital sigma hole on the halogen similar to the electrostatic s hole manifested in the molecular electrostatic potential. The predicted high halogen-bond-acceptor affinity of N-heterocyclic carbenes was evidenced in the highest complexation energy for the hitherto unknown CF3I center dot NHC complex. The dominant NOCV orbital represents an electron-density deformation according to a n ->sigma*-type interaction. The characteristic signal found in the reduced density gradient versus electron-density diagram corresponds to the non-covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory. The unexpected C-X bond strengthening observed in several cases was rationalised within the molecular orbital framework.

Excited-state properties, although extremely useful, are hardly accessible. One indirect way would be to derive them from relationships to ground-state properties which are usually more readily available. Herewith, we present quantitative correlations between triplet excited-state (T-1) properties (bond dissociation energy, D-0(T1), homolytic activation energy, E-a(T1), and rate constant, k(r)) and the ground-state bond dissociation energy (D-0), taking as an example the photodissociation of the C-Si bond of simple substituted allylsilanes CH2=CHC((RR2)-R-1)-SiH3 (R-1 and R-2 = H, Me, and Et). By applying the complete-active-space self-consistent field CASSCF(6,6) and CASPT2(6,6) quantum chemical methodologies, we have found that the consecutive introduction of Me/Et groups has little effect on the geometry and energy of the T-1 state; however, it reduces the magnitudes of D-0, D-0(T1) and E-a(T1). Moreover, these energetic parameters have been plotted giving good linear correlations: D-0(T1) = alpha(1) + beta(1) . D-0, E-a(T1) = alpha(2) + beta(2) . D-0(T1), and E-a(T1) = alpha(3) + beta(3) . D-0 (alpha and beta being constants), while k(r) correlates very well to E-a(T1). The key factor behind these useful correlations is the validity of the Evans-Polanyi-Semenov relation (second equation) and its extended form (third equation) applied for excited systems. Additionally, the unexpectedly high values obtained for E-a(T1) demonstrate a new application of the principle of nonperfect synchronization (PNS) in excited-state chemistry issues. Journal of Physical Chemistry A

The Fukui matrix is introduced as the derivative of the one-electron reduced density matrix with respect to a change in the number of electrons under constant external potential. The Fukui matrix extends the Fukui function concept: the diagonal of the Fukui matrix is the Fukui function. Diagonalizing the Fukui matrix gives a set of eigenvectors, the Fukui orbitals, and accompanying eigenvalues. At the level of theory used, there is always one dominant eigenvector, with an eigenvalue equal to 1. The remaining eigenvalues are either zero or come in pairs with eigenvalues of the same magnitude but opposite sign. Analysis of the frontier molecular orbital coefficient in the eigenvector with eigenvalue 1 gives information on the quality of the frontier molecular orbital picture. The occurrence of negative Fukui functions can be easily interpreted in terms of the nodal character of the dominant eigenvector versus the characteristics of the remaining eigenvectors and eigenvalues.

The concept of bond ionicity, obtained via a valence bond analysis, is invoked in the interpretation of the catalytic activity of supported vanadium oxides, in analogy with previous work conducted within the framework of conceptual DFT. For a set of model clusters representing the vanadium oxide supported on SiO(2), Al(2)O(3), TiO(2), ZrO(2), the ionic character of the vanadium-oxygen bond, involved in the dissociative adsorption of methanol on the catalyst, wasquantified. Detailed scrutiny shows that this ionicity increases from the Al through the Zr support, in agreement with the increasing catalytic activity through this series; the case of the Si supported oxide is found to be an exception however, giving rise to the most ionic V-O bond of the different compounds studied. This finding is confirmed by calculations on smaller clusters focusing on detail in the pi back bonding. (C) 2011 Elsevier B. V. All rights reserved.

Based on the so-called Hirshfeld atom in the molecule scheme, a new AIM method is presented. The method is similar to the Hirshfeld-I scheme, with the AIM weight function being constructed by minimizing the information loss upon formation of the molecule, but now requiring explicitly that the promolecular densities integrate to the same number of electrons as the AIM densities. This new weight function leads to a new iterative AIM scheme, and the resulting operative scheme is examined and discussed. The final results indicate that the newly proposed method does not perform as well as the Hirshfeld-I method.

We applied the internal photoemission technique to the direct observation of deep levels together with barrier heights and band discontinuities at different semiconductor heterostructure interfaces. Its performances and capabilities are superior to those of established techniques: the energy resolution is excellent and it can be applied to "real" device interfaces under bias. The technique was successfully tested for the Pd/n-GaAs and Pd/a-Si:H Schottky barriers as well as for the a-Ge/n-GaAs and a-Ge/p-GaP heterojunctions. We found a Pd/n-GaAs Schottky barrier height of 0.78 eV and an a-Ge/n-GaAs valence band discontinuity of 0.42 eV; in both cases the Fermi level was "pinned" at an averaged value of 0.76+/-0.03 eV above the top of the GaAs valence band. Furthermore we directly measured a feature at 1.09 eV, due to Pd-induced empty states approximately 1.1 eV above the valence band. The Pd/n-GaAs Schottky barrier also exhibits a feature at 1.36 eV, explained by transitions from the valence band to a localized state, made possible by the band bending. In the case of a-Ge/n-GaP we found a DELTA-E(V) = 0.88 +/- 0.05 eV and a DELTA-E(C) = 0.68 +/- 0.05 eV. Finally, in the Pd/a-Si:H Schottky barrier, we demonstrated the contribution of resonant tunneling through localized states of the conduction band.

Using O 1s x-ray photoelectron and Mg KL23L23 Auger spectroscopy, we demonstrate that monolayer MgO(100)/Ag(100) exposed at 300 K to H2O vapor pressure of 10(-8) Torr is strongly hydrated up to 0.8 H2O per MgO formula unit, half of the water molecules being dissociatively adsorbed at the fourfold coordinated surface oxide sites. These dramatic hydrolysis and molecular adsorption phenomena are strikingly different from those observed at perfect bulklike MgO(100) surfaces, and provide strong experimental support to the concept of unprecedented interactions and properties at oxide-metal interfaces.

The nature of rate-retarding effects of cationic micelles on the water-catalyzed hydrolyses of a series of para-substituted 1-benzoyl-1,2,4-triazoles (1a-f) and 1-benzoyl-3-phenyl-1,2,4-triazole (2) has been studied using kinetic methods. A comparison is drawn between medium effects in the micellar Stern region and in model solutions for the micellar Stern region. Simple model solutions involving concentrated aqueous solutions of a small ionic molecule resembling the surfactant headgroup, as reported before,1 were improved. New model solutions for alkyltrimethylammonium bromide micelles contain both tetramethylammonium bromide (TMAB), mimicking micellar headgroups, and 1-propanol, mimicking hydrophobic tails. The rate-retarding effect of micelles on the hydrolysis of 1a-f and 2 is caused by the high concentration of headgroups as well as by hydrophobic tails in the Stern region where 1a-f and 2 bind to the micelle. Individual contributions of these interactions are quantified. Rate-retarding effects found for different probes, with different sensitivities for interactions as they occur when the probe binds to the micellar Stern region, as well as the micellar Stern region’s micropolarity as reported by the ET(30) probe, are satisfactorily reproduced by new model solutions containing both TMAB and 1-propanol.

Hetero Diels-Alder reaction of oxadienes with 3,4-epoxy-2-methyleneoxolanes gave the corresponding 3,4-epoxy-1,6-dioxaspiro[4,5]-dec-7-enes with high stereoselectivity. Good yields of adducts were obtained in the presence of mild Lewis acis, such as zinc or stannous chloride. The spiroketal adducts have been transformed chemio- and stereospecifically by either hydrogenation, hydride reduction or acid catalyzed isomerization. The stereochemical outcome of the cycloadditions has been investigated. The spiroketal adducts always result from an oxadiene addition anti relative to the allylic epoxy substituent. When the oxadiene is substituted suitably as in crotonaldehyde, we demonstrated that the cycloaddition is totally endo selective relative to the enol ether function. Ab initio calculations suggested that 3,4-epoxy-2-methyleneoxolane and 3,4-epoxy-3-methyl-2-methyleneoxolane adopt envelopw conformations with the oxygen atom of the oxolane moiety pointing toward the epoxide ring. No significant distortion from planarity was calculated for the exocyclic double bond of these dienophiles.