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Pericyclic reactions are powerful transformations for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. Their role in biosynthesis is increasingly apparent, and mechanisms by which pericyclases can catalyse reactions are of major interest.sup.1. [4+2] cycloadditions (Diels-Alder reactions) have been widely used in organic synthesis.sup.2 for the formation of six-membered rings and are now well-established in biosynthesis.sup.3-6. [6+4] and other 'higher-order' cycloadditions were predicted.sup.7 in 1965, and are now increasingly common in the laboratory despite challenges arising from the generation of a highly strained ten-membered ring system.sup.8,9. However, although enzyme-catalysed [6+4] cycloadditions have been proposed.sup.10-12, they have not been proven to occur. Here we demonstrate a group of enzymes that catalyse a pericyclic [6+4] cycloaddition, which is a crucial step in the biosynthesis of streptoseomycin-type natural products. This type of pericyclase catalyses [6+4] and [4+2] cycloadditions through a single ambimodal transition state, which is consistent with previous proposals.sup.11,12. The [6+4] product is transformed to a less stable [4+2] adduct via a facile Cope rearrangement, and the [4+2] adduct is converted into the natural product enzymatically. Crystal structures of three pericyclases, computational simulations of potential energies and molecular dynamics, and site-directed mutagenesis establish the mechanism of this transformation. This work shows how enzymes are able to catalyse concerted pericyclic reactions involving ambimodal transition states. Enzymatic catalysis of pericyclic [6+4] cycloaddition reactions to form ten-membered rings is observed during biosynthesis of the macrocyclic antibiotic streptoseomycin, and the mechanism of these transformations is established., Author(s): Bo Zhang [sup.1] , Kai Biao Wang [sup.1] , Wen Wang [sup.1] , Xin Wang [sup.2] , Fang Liu [sup.2] , Jiapeng Zhu [sup.3] , Jing Shi [sup.1] , [...]

A series of six-membered rings bearing cis oriented vicinal carboxylate and sulfinate esters were treated with Grignard reagents with the intention of transforming them to p-carboalkoxy substituted sulfoxides. The expected outcome did not transpire and instead the substrates demonstrated the capacity to accept 3 equiv. of organometallic agent in an uncontrollable manner. As such, the substrates possessing eclipsing carboxylate and sulfinate esters accepted two organic ligands at the carboxylate functionality and one at the sulfinyl group. When isomer mixtures of sterically encumbered sulfinate esters were reacted, a single sulfoxide stereochemistry resulted. A mechanism involving the intermediacy of a sulfurane is proposed to account for the experimental observations. Key words: Grignard reagent, sulfinate ester, sulfoxide, addition reaction, sulfurane. Une serie de cycles a six membres portant des esters carboxyliques et sulfiniques vicinaux ont ete traites avec des reactifs de Grignard dans le but de les transformer en p-carboalkoxy sulfoxydes substitues. Le resultat espere n'a pas ete obtenu et, au lieu de cela, les substrats ont montre une capacite a accepter trois equivalents d'agent organometallique de maniere incontrolable. En tant que tels, les substrats portant des esters carboxyliques et sulfiniques en position eclipsante ont accepte deux ligands organiques au niveau de la fonction carboxylate et un au niveau du groupe sulfinyl. La reaction de melanges isomeriques d'esters sulfiniques steriquement encombres a debouche sur une seule stereochimie du sulfoxyde. Un mecanisme impliquant l'intermediaire d'un sulfurane est propose, qui permet d'expliquer les observations experimentales. [Traduit par la Redaction] Mots-cles : reactif de Grignard, ester sulfinique, sulfoxyde, reaction d'addition, sulfurane., Introduction For some time, sulfur containing functionality have been recognized as substituents that activate alkenes for the Diels-Alder cycloaddition. (1-10) The sulfone and sulfoxide containing adducts so formed can be [...]

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 stereo-selectivity for 10-link compounds (cis/trans = 70:30), while 11- and 12-links compounds exhibit no particular selectivity. DFT (B3LYP/6-31[G.sup.*]) 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. Key words: Diels-Alder, stereoisomer, DFT, reactivity. Les reactions Diels-Alder intra-moleculaires (IMDA) de trienes attaches peuvent conduire a deux diastereoisomeres distincts, un stereoisomere cis (i.e., endo) et un trans (i.e., exo). L'experience montre une grande cis stereo- selectivite pour les composes a 10 chainons (cis/trans = 70:30) alors que ceux a 11 et 12 chainons ne montrent pas de selectivite particuliere. Des calculs DFT (B3LYP/6-31[G.sup.*]) fournissent un apercu des raisons de cette etrange stereo-selectivite. Le chemin de cyclisation vers le stereo-isomere trans est toujours thermodynamiquement favorise quelle que soit la taille du systeme. La grande stereoselectivite affichee pour le compose a 10 chainons est cinetiquement controlee par une concurrence entre les effets de contrainte de cycle et les effets electroniques a l'etat de transition. Le descripteur dual de reactivite chimique, issu de la DFT conceptuelle pour delineer les effets electroniques, a ete utilise pour eclaircir les mecanismes stabilisants ayant lieu a l'etat de transition. Mots-cles: Diels-Alder, stereoisomere, DFT, reactivite., Introduction Bio-molecules often contain one or several cycles that may or may not involve a hetero-atom. They generally exhibit biologic activities, and it can be desirable to be capable of [...]

The type 2 intramolecular N-acylazo Diels-Alder reaction has provided a regio- and stereoselective synthesis of bicyclic 1,2-diazine systems. The sequence of transformations has presented a route for the regioselective synthesis of medium-ring nitrogen heterocycles and 1,4-diamines.

A two-state mechanism is described for the CpCo-catalyzed [2@@] cyclotrimerization of substituted alkynes that includes all putative intermediates. The feasibility of direct Diels-Alder cycloaddition pathways are established when cobaltacyclopentadienes are exposed to dimethyl butynedioate (DMAD).

Resume : Dans ce travail, nous avons etudie theoriquement les reactions de Diels-Alder a demande inverse d'electrons entre le 4-aza-6-nitrobenzofuroxane 1 et les dienophiles de type 3a-3c. Nous avons discute [...]

A novel and highly diastereoselective method is described for the preparation of polycyclic indole derivatives through the intramolecular imino Diels-Alder reaction of aminoanthraquinone with N-prenylated indole-2-carboxaldehydes in the presence of triphenylphosphonium perchlorate (TPPP). The technique is simple and easy as it initiates from readily available starting substances.

An anionic intramolecular Diels-Alder process is found to be taking place in the base-promoted cycloaddition reactions of 1-aryl-4-oxahepta-1,6-diyne systems in DMSO, though the reaction exhibits temporary disruption of aromaticity. The results show that the described technique is an extremely fast process and hence can be used to produce diversified and substituted products.

A study was conducted to investigate the double Diels-Alder cycloaddition of two tethered isobenzofurans to the fullerene [C.sub.60]. The method helps to easily perform the saturation of two of the three C=C double bonds within a six-membered ring of [C.sub.60] and provides the means of saturating the remaining double bond of a six-membered ring of [C.sub.60] via the side chains of the isobenzofurans with suitably reactive functional groups.

A study was conducted to examine the reactions of 1,3-disubstituted isobenzofurans with the fullerene [C.sub.60] in the context of an approach to open a large orifice on the fullerene framework. The thermal stability of the adducts toward retro-Diels-Alder fragmentation differs greatly in solution from that in the solid state which suggest that they could be stored at room temperature in the solid state for several weeks without significant decomposition but have to be handled within several hours in solution.

Four novel metal/amine catalysts have converted Boc-NOHO to its acylnitroso species at 5 mol % catalyst loading. These reactions have helped in the preparation of polyfunctional hetero Diels-Alder adducts in high yield and from the commercially available materials.

A new type of cross/coupling/cycloaddition cascade is developed and used in the total synthesis of some members of the hydroxylated phenanthridone subclass of the Amaryllidaceae alkaloid family. The alkaloids are assembled by a one-pot Stille/intramolecular Diels-Alder reactioncascade and the resulting cycloadducts are used for the stereocontrolled installation of other functionality present in the C-ring of the target molecules.

Four novel metal/amine catalysts have converted Boc-NOHO to its acylnitroso species at 5 mol % catalyst loading. These reactions have helped in the preparation of polyfunctional hetero Diels-Alder adducts in high yield and from the commercially available materials.

A study evaluates the role of achiral pyrazolidinone templates in conjunction with chiral Lewis acids in room temperature, enantioselective Diels-Alder cycloadditions. Observation of high selectivities are reported in reactions with chiral Lewis acids derived from relatively small chiral ligands, suggesting that pyrazolidinone templates are capable of relaying stereochemical information from the ligand to the reaction center.

The bonding evolution theory (BET) is used to investigate two Diels-Alder (DA) type reactions, that is, normal electron demand (NED) between 1, 3-butadiene (BD) and acrolein (Acr) and inverse electron demand (IED) between 2, 4-pentadienal (PDA) and methyl vinyl ether (MVE). The results have shown that well formed bonding basin V([C.sub.1],[C.sub.6]) is observed only for the PDA...B[H.sub.3]/MVE reaction in the transition structure.

Atomic force microscopy and differential pulse voltammetry were used to characterize the interaction of small highly structured ribozymes with two carbon electrode surfaces. The ribozymes spontaneously self-assemble in two-dimensional networks that cover the entire HOPG surface uniformly. The full-length ribozyme was adsorbed to a lesser extent than a truncated RNA sequence, presumably due to the formation of a more compact overall structure. All four nucleobases composing the ribozyme could be detected by anodic voltammetry on glassy carbon electrodes, and no signals corresponding to free nucleobases were found, indicating the integrity of the ribozyme molecules. [Mg.sup.2+] cations significantly reduced the adsorption of ribozymes to the surfaces, in agreement with the stabilization of this ribozyme's compact, stable, and tightly folded tertiary structure by [Mg.sup.2+] ions that could prevent the hydrophobic bases from interacting with the HOPG surface. Treatment with [Pb.sup.2+] ions, on the other hand, resulted in an increased adsorption of the RNA due to well-known hydrolytic cleavage. The observed dependence of anodic peak currents on different folding states of RNA may provide an attractive method to electrochemically monitor structural changes associated with RNA folding, binding, and catalysis.

The hetero Diels-Alder reaction of vinyl allenes and aldehydes in the presence of a Lewis acid is studied both experimentally and theoretically. Theoretical calculations using the density functional theory indicate that the reaction proceeds through a highly asynchronous polar transition state.

A Diels-Alder strategy is used in a concise total synthesis of xestodecalactone A. Diels-Alder cycloaddition reactions involving 1,3-disubstituted nonequivalent allene dienophiles have resulted with modest chemoselection in difficultly predictable ways.

A ring-closing metathesis (RCM) mediated, pathway to trifluoromethyl-containing piperidines is detailed, which involves the development of a synthetic route to a new (trifluoromethyl)allylating reagent through a Diels-Alder/retro-Diels-Alder strategy. The findings established that RCM represents a viable pathway to several classes of biologically relevant trifluoromethylated piperidine derivatives.

Total synthesis of two new kempane derivatives were achieved with transannular Diels-Alder reaction (TADA) serving as the key step for the stereoselective formation of tricyclic [6.6.5] system. The synthetic approach also reveals that the geometry of the C3 group of such a tricyclic system plays an important role for the formation of the seven membered kempane skeleton.

Full details of a systematic exploration of the intramolecular [4@]/[3@] cycloaddition cascade of 1,2,4-oxadiazoles are disclosed in which the scope and utility of the reaction are defined. Conducted largely with the concurrent development of a synthetic approach to vindoline and relative to the intermoelcular reaction cascade, the studies extend the alkenes and oxadiazoles that participate in the reaction.

A detailed investigation was conducted on the mechanism of enantioselective, hydrazide-catalyzed Diels-Alder cycloaddition. Mechanistic studies using NMR showed the occurrence of a retro Diels-Alder reaction during the catalytic cycle, suggesting a thermodynamic component in the reaction.

A mild, thermal Alder-ene reaction of enalles is developed. The allenic double bond acts as the 'ene' and generates a carbon-carbon bond to an unactivated olefinic 'enophile' in DMF at 120 degree Celsius to give [n.3.0]bicyclic systems (n = 3 -5) in good yields.

The results on the experimental and computational studies of the hydrogen-bond-promoted enantioselective hetero-Diels-Alder reaction of Danishefsky's diene with benzaldehyde are reported. The results indicate that carbonyl group of benzaldehyde is activated by forming an intermolecular hydrogen bond with one of the hydroxyl groups of the alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanol molecule.

The preparation of the symmetrical heptacyclic core of the spiro 6-6-5-5 ritterazines is reported. It is expected that the key Diels-Alder/Wittig/diene cyclozirconation approach illustrated, supported by ZINDO calculations, would be a general strategy for the stereocontrolled construction of polycarbacyclic target structures.

An efficient and rapid synthesis of fluoroalkylated enones, bearing various fluoroalkyl moieties is described. It is concluded that beta-fluoroalkylated enones constitute efficient dienophiles for Diels-Alder cycloadditions and that the presence of the fluorinated moiety both increased the reactivity of these compounds and implied modification of the stereoselectivity.

A highly efficient strategy is developed for the rapid asymmetric synthesis of gem-dimethyl and spirocyclopropyl norbornyl carboxylic acids. The key transformation involved the unprecedented asymmetric Diels-Alder reaction of highly reaction beta,beta-cyclopropyl-alpha,beta-unsaturated N-acyloxazolidinoones with cyclopentadiene affording the adducts in high yield and de.

14β-Fluorosteroids 3 and 4 were synthesized to give a new class of unnatural cardenolides. The total synthesis of racemic 14β-fluorosteroids was accomplished using a highly diastereoselective transannular Diels--Alder reaction on a trans-cis-cis macrocyclic triene. The α-fluoro analog 4 provided a comparable inhibitory activity to natural digitoxigenin 1. Key words: fluorosteroid, bioisostere, cardiovascular diseases, transannular Diels--Alder reaction (TADA), macrocyclization. Les 14β-fluorosteroides 3 et 4 ont ete synthetises en vue d'obtenir une nouvelle classe de cardenolides nonnaturels. La synthese totale racemique des 14β-fluorosteroides a ete accomplie en utilisant la reaction diastereoselective de Diels--Alder transannulaire a partir d'un triune macrocyclique trans-cis-cis. L'α fluoro-analogue 4 donne une activite inhibitrice comparable a la digitoxigenine 1. Mots cles : fluorosteroide, bioisostere, maladies cardiovasculaires, reaction de Diels-Alder transannulaire (DATA), macrocyclisation., Introduction The (+)-digitoxigenin 1 is derived from the biologically active trisaccharide digitoxin 2, which is extracted from the Digitalis purpura plant (1) (Fig. 1). These cardenolide steroids belong to the [...]

A gas phase study of substituent effects on the stereochemistry of both intermolecular Diels-Alder (IMDA) reactions of 9-E- and 9-Z-substituted pentadienyl acrylates and intermolecular Diels-Alder (DA) reactions between butadiene and monosubstituted alkenes and 3-substituted acrylates is reported. Cis/trans selectivity for IMDA reactions involving 9-E-substituted pentadienyl acrylates generally follows the normal pattern found for corresponding intermolecular Diels-Alder reactions.

The reaction rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthrance in CO(sub 2) + ethanol and CO(sub 2) + hexane mixed solvents of different compositions were determined by in situ UV/vis spectroscopy at 318.15 K and different pressures. The result states that at the same temperature the reaction can not be conducted in pure supercritical CO(sub 2) in the highly compressible region due to the solubility limitation of 9-hydroxymethylanthrance in supercritical CO(sub 2) at the lower pressures, while the reaction can be carried out in the highly compressible mixed solvents, and reaction rate is effective by pressure.

The two complementary procedures for the 'one-pot' synthesis of highly substituted pyridines, one using microwave irradiation as the key technological advance and the second approach based on tethered imine-enamine (TIE) methodology is described. Both routes do not need discrete aromatization step and offer significant advantages over the classical methods giving a wide variety of tri-, tetra-, and penta-substituted pyridines in high optimized yields.

An anionic cyclization strategy developed in our laboratory was used to produce a versatile and convergent synthesis of an advanced tetracyclic intermediate for the construction of ouabagenin and closely related analogs. Key words: organic chemistry, synthesis, cycloaddition, polycyclization, Michael reaction, Diels-Alder reaction, steroids, oubain, ouabagenin, natural products. L'utilisation d'une reaction de cyclisation anionique developpee dans nos laboratoires a permis d'elaborer une route convergente et versatile d'un intermediaire tetracyclique pour la synthese de la ouabagenine et ses derives. Mots cles : chimie organique, synthese, cycloaddition, polycyclisation, reaction Michael, reaction Diels-Alder, steroides, ouabaine, ouabagenine, produits naturels.

D-Isoascorbic acid was converted to the tetraenone 12 to examine its behaviour in the intramolecular Diels-Alder reaction with pendant dienes in a diene-transmissive environment. These studies were directed toward the synthesis of the hydrindenone nucleus via a tether-controlled Diels-Alder reaction. It was anticipated that this would lead to a diene-transmissive strategy for steroids such as Desogestrel[R]. In contrast to out previous studies with decalins, the dominant isomer (150 [degrees]C) was the bicyclo[3.3.1]nonadieneone adduct 23, and none of fused adduct 27 was detected. These products were accompanied by two minor hydrindenone adducts 24 and 25. The isomer ratio was dependent on the temperature of the reaction. Key words: Diels-Alder, hydrindane, pentadienylation, intramolecular cycloaddition, bicyclo[3.3.1]nonenone. L'acide D-isoascorbique a ete transforme en tetraenone 12 dans le but d'etudier son comportement dans la reaction intramoleculaire de Diels-Alder avec des dienes pendants, dans un environnement permettant une transmission. Ces etudes ont ete dirigees vers la synthese du noyau hydrindenone via une reaction de Diels-Alder controlee par une laisse. Il etait prevu que cette methode permettrait de developper une strategie dienique permettant une transmission pour realiser la synthese de steroides tel le Desogestrel[R]. Par opposition aux etudes anterieures realisees dans ce laboratoire avec des decalines, l'isomere dominant (150 [degrees]C) est l'adduit bicyclo[3.3.1]nonadienone 23 et on n'a pas detecte la presence du produit condense 27. Ces produits etaient accompagnes de deux adduits hydrindenones mineurs, 24 et 25. Le rapport des isomeres varie avec la temperature de la reaction. Mots cles: Diels-Alder, hydrindane, pentadienylation, cycloaddition intramoleculaire, bicyclo[3.3.1 ]nonenone. [Traduit par la Redaction]

The intramolecular inverse-electron-demand Diels-Alder reaction between imidazoles and 1,2,4-triazines linked by a trimethylene tether from the imidazole N1 position to the triazine C3 proceed in excellent yields to produce 1,2,3,4-tetrahydro-1,5-naphthyridines. The reaction to produce the tetrahydro-1,5-naphthyridines can also be promoted with microwave irradiation.

A new and clean method that yields free S2O by a hetero retro-Diels-Alder reaction is presented. The computational rationalization of the chemical properties of S2O and its disproportionation to SO2 and S3 is described.

Strategies for the construction of cyclic molecules containing variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems) are described. These routes employ a multi-component coupling protocol that utilizes sequential magnesium-mediated carbometallation of propargyl alcohols and intramolecular Diels-Alder reactions (IMDA). The cycloaddition generates the key eight-membered taxane ring as a single diastereomer, induced by preferential Lewis acid (diethylaluminum chloride or boron trifluoride etherate) complexation with the cross-ring oxygens. Both the electronic nature of the dienophile and the neighbouring group non-bonded interactions contribute to the success of these cycloadditions. Key words: magnesium chelate, Lewis acid, intramolecular Diels-Alder, cycloaddition.

The extension of our strategies for the construction of cyclic molecules containing variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems) for the synthesis of the tricyclo[9.3.1.0 (3,8)]pentadecenone (ABC taxane ring system) and bicyclo[2.2.2]octanones are described. These routes employ a multi-component coupling protocol that employs sequential magnesium-mediated carbometallation of allyl-substituted propargyl alcohols followed by diastereoselective Lewis acid catalyzed intramolecular Diels-Alder reactions (IMDA). Subsequent ring-closing metathesis (RCM) afforded the ABC taxane core structure. Enone accelerated [3,3] sigmatropic rearrangements (Cope rearrangements) generated the bicyclo[2.2.2]octanone nucleus. In the presence of a Lewis acid, the dienophile precursor underwent a tandem reaction via the adduct directly to the bicyclo[2.2.2]octanones. This is the first example of a novel enone accelerated carbocycle Cope rearrangement and provides direct access to bicyclo[2.2.2]octanones by a new route that compliments the traditional cyclohexadiene cycloaddition approach. Key words: magnesium chelate, Lewis acid, taxanes, Diels-Alder, sigmatropic rearrangement, oxy-Cope, ring-closing metathesis, bicyclo[2.2.2]octanone.

N-Benzoyl- and N-arylsulfonyl-p-benzoquinone-mono-imine ketals (QIKs) undergo smooth Diels-Alder cycloadditions with typical 1,3-butadienes to yield the expected endo adducts. Treatment with catalytic acid rapidly converts the adducts to dihydronaphthalenes. The N-benzoyl derivatives require high pressures for cycloadditions while the N-tosyl and N-nosyl derivatives proceed under thermal (ambient pressure) conditions. In all cases the cycloadditions are completely regioselective. Key words: Diels-Alder, quinone imine ketal, hyperbaric chemistry.

A general and streamlined method for the construction of benzannulated bi- and polycyclic frameworks is developed and its scope and limitations are explored. On the basis of the photonlization of substituted benzaldehydes and subsequent Diels-Alder trapping of the generated hydroxy-o-quinodimethanes, this method is optimized to set the stage for the total synthesis of several naturally occurring members of the hamigeran class.

3-Ferrocenyl-2,4,5-tri-([beta]-naphthyl)cyclopentadienone undergoes a Diels--Alder reaction with di-([beta]-naphthyl)acetylene to yield, after elimination of carbon monoxide, ferrocenyl-penta-([beta]-naphthyl)benzene (4). [sup.1]H and [sup.13]C variable-temperature NMR studies on 4 reveal the existence of multiple diastereoisomers at low temperature. These data are interpreted in terms of slowed rotation of the naphthyl groups, and are supported by the X-ray crystal structure of 4, which exhibits disorder at three of the naphthyl sites. Key words: sterically crowded molecules, hindered rotations, crystallography, NMR.

A series of monolayer-protected clusters (MPCs) modified with a photoreactive [4-(11-mercaptoundecyl)phenyl](2-methylphenyl)methanone (1) moiety have been prepared where 1 is co-absorbed to the MPC surface with dodecanethiol, octadecanethiol, or 11-mercaptoundecanoic acid methyl ester. Upon irradiation the MPC-anchored 1 reacts efficiently through its triplet excited states, yielding 1,4-biradicals that collapse to synthetically useful, long-lived photodienol intermediates, which can be efficiently trapped in Diels-Alder type chemistry by dienophiles--namely, dimethyl acetylenediearboxylate (DMAD). In all cases the Diels-Alder trapping of the dienol occurred efficiently resulting in > 60% conversion to the Diels-Alder adduct. This indicates that the local environment surrounding 1 did not influence its ability to react via the Diels-Alder reaction; however, the reaction could not be taken to completion. The inability to react completely is attributed to 1 binding to distinct sites on the MPC core; there are edge, vertice, and terrace sites. Selective population of these specific sites and the subsequent irradiations show that MPCs with 1 anchored predominantly at edge and verfice sites results in an extent of reaction of 85 [+ or -]3%, whereas selectively populating the terrace sites results in an extent of reaction of 36 [+ or -] 2%. These results suggest that 1 anchored to edge and vertice sites is more reactive to the Diels-Alder reaction than that involving terrace sites. Key words: monolayer protected cluster, site selective reactivity, Diels-Alder, photochemistry.

The structure of Copper(II) complex formed within the course of a stereoselective Diels-Alder reaction was investigated by EXAFS, CW-EPR at X- and W-band, HYSCORE, pulsed ENDOR, and UV-vis spectroscopy. The experimental techniques indicate that the chiral bis(sulfoximine) ligand (S,S)-1 and the dienophile forma tetragonally distorted complex in CH2Cl2.

The exo and endo Diels-Alder adducts of p-methoxycarbonylbenzyl trans-1, 3-butadiene-1-carbamate and N, N-dimethylacrylamide is synthesized, and the absolute configurations of resolved enantiomers are determined. The Diels-Alder reactions are one of the most powerful carbon-carbon bond-forming processes in organic chemistry.

Several tetracyclic molecules were prepared by diene-transmissive Diels-Alder cycloadditions. Control over the stereochemical outcome of the cycloaddition was achieved and the structural features of the precursors affecting the stereochemistry is discussed. Useful information was gathered concerning the factors governing this stereocontrol, which will be indispensable for the future of this strategy. Key words: quassinoid, anticancer agent, diene-transmissive Diels-Alder cycloaddition, oxadiene, hetero Diels-Alder.

Research has been conducted on Diels-Alder reactions of phosphaethene with isoprene and 1,3-butadiene. Reaction results have revealed asynchronous transition structures and that the DFT activation energies of these reactions are low.

Research has been conducted on the Diels-Alder adducts between benzoquinones and cyclopentadienes. The reduction of these adducts to the corresponding diols has been carried out and the results demonstrate that the treatment of these diols with acid has produced a skeletal rearrangement reaction.

Research has been conducted on the phosphonoacrolein. The synthesis of the compound performed via the acidic treatment of beta-ethoxy-alpha-(methoxymethyl)vinylphosphonate is described.

Research has been conducted on the Diels-Alder reactions. The kinetics of cyclopentadiene, sorbyltrimethylammonium bromine and sorbyl alcohol reactions with N-substituted maleimides carried out in micellar media has been investigated and the details are reported.

Research has been conducted on anhydrolycorinone. The synthesis of this compound carried out via sequential intramolecular Doels-Alder reactions of the substituted 2-amino-1,3,4-oxadiazole is described.

Research has been conducted on the Diels-Alder reactions. The study of the di-2-azulenylacetylene with tetraphenylcyclopentadienone carried out via autoxidation of the azylenylbenzene derivative to produce 7,8,9,10-tetraphenyldiazuleno[2,1-a:1,2-c]naphthalene is presented.