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Cyclopentadienes, 2H-phospholes can act both as dienes and dienophiles. 2H-phospholes can readily deprotonated to give highly aromatic anions and can readily react with transition metal derivatives to give n5-complexes representing a diagonal phosphorus-carbon analogy.

The results presented for the rate acceleration of the Diels-Alder reaction of metal-complexed oligoether quinones with cyclopentadiene have demonstrated a development of self-activated supramolecules. The self-activated supramolecules are expected to have potential utility for catalytic reactions, regio-selective reactions, asymmetric reactions, photonic reactions, and biochemical reactions.

The study of valuable mechanistic insight into the intricacies and complexities of the rearrangement of housane-derived radical cations has been provided. It is demonstrated that structural changes allow manipulation of the conformational effects in the rearrangement of cyclopentane-1,3-diyl radical cations such that either stereochemical memory or Curtin-Hammett behavior is observed.

The rotational orientation of cyclopentadienyl rings, their effect on d-orbital energy levels and splitting in transition metal complexes are described. The possibility of using sterically imposed ligand rotation as a means of spin-state manipulation makes indenyl compounds a potentially rich source of magnetically adjustable molecules.

Reaction paths for ground-state 2-cyclopentenone and 3-cyclopentenone due to the electrophilic addition of O(3P) were investigated.

Research has been conducted on the Diels-Alder reactions of 1,4-benzoquinones with cyclopentadiene. Formation of diastereoisomeric endo-adducts that result from the reaction is discussed.

Subjection of ethyl (Z)-2-carbomethoxyethenesulfinate and ethyl (E)-2-carbomethoxyethenesulfinate to cyclopentadiene is examined. Results indicate their reactivity to Diels-Alder reactions.

Stereoselectivities of Diels-Alder reactions and ionic effects on them are discussed relative to the cyclopentadiene (CP)-methyl acrylate (MA) reaction in aqueous LiCl, NaBr, NaCl, CaCl(sub.2), and LiClO(sub.4) and guanidinium chloride. The variations in endo- and exo-stereoselectivities were studied in salt-solvent reaction media (SSRM) with varying salt concentrations. Endo/exo ratios are sensitive to the ionic concentrations. The scaled particle theory was used to calculate contributions of cavitation and solvation effects.

Research was conducted to examine the effectivity of the hyperconjugative interaction of cyclopentadiene. Cyclopentadienes have demonstrated considerable enhanced cyclic conjugation in comparison with the parent molecule, C5H6. They also exhibit an enhanced diamagnetic susceptibility anisotropy but show no evidence for aromaticity. Interpretations of previous observations on reactivity are based on the observed aromatic stabilization.

Research was conducted to examine the conversion of the enantio- and diastereomerically pure amido acid into enantiomerically pure cyclopentane derivatives. The objective was to show how the combination of a Diels-Alder reaction between cyclopentadiene derivatives and maleic anhydride, followed by desymmetrization and ozonolysis can be applied to an enantio- and diastereocontrolled synthesis of highly substituted cyclopentanes. Results reveal that the method provides a versatile and concise approach to the synthesis of enantiomerically pure tetra- and penta-substituted cyclopentanes in which the cyclopentane substituents are syn to one another.

Research was conducted to examine novel ferrocene-modified hydrogen-bonding structures as rationally designed new artificial nucleobase receptors. For the hydrogen-bonding moiety, diamidopyridine was used while several polynuclear aromatics were chosen for pi-stacking one. Results indicate the dependence of the binding affinity of the receptors to 1-butylthymine on the aromatic structures. The value of the pivot character of the ferrocene for construction of the intermolecular interaction site was also clarified.

The synthesis of the organometallic complexes of Co(I) and Co(III) with the same ligands using either the functionalized cyclopentadiene or its Li15, or Na16 salts is described. Cyclopentadienyllithium or -sodium salts are used as reagents for the introduction of cyclopentadienyl ligands. Results implied that metallocene-type complexes and half-sandwich compounds of cobalt containing the ((dimethylamino)ethyl)cyclopentadienyl ligand can be synthesized easily. It was also observed that protonated Co(III) complexes can be characterized by special solubility in water and polar solvents.

The first example of migration of a hypervalent phosphorus fragment is presented with the reaction of iron phosphorane complexes Cp(CO)2Fe(P(OC6H4Y)(OC6H4Z)) with lithium diisopropylamide and MeI to yield (eta5-C5H4P(OC6H4Y)(OC6H4Z))(CO)2FeMe. A proton abstraction on the Cp ring by LDA initiates the reaction, after which the phosphorane fragment migrates to the Cp ring to (eta5-C5H4P(OC6H4Y)(OC6H4Z))(CO)2Fe-. The latter is then converted into (eta5-C5H4P(OC6H4Y)(OC6H4Z))(CO)2FeR by treating it with alkyl halide.

The Diels-Alder reactions of cyclopentadiene with menthyl acrylate catalyzed by AlCl3 and with acrolein catalyzed by menthoxyaluminum dichloride are described. The low screening effect of the menthyl group is explained by citing the weak steric hindrance of the most stable stacked conformations. A reaction model for the menthoxy-aluminum dichloride-catalyzed cycloaddition between cyclopentadiene and acrolein is then proposed.

Research was conducted to examine the heteroatom derivatives of cyclopentadienylaluminum and to determine the x-ray crystal structure of (eta5-C5H5)(2,6-t-Bu-4-Me-C6HO)2Al. The cyclopentadienylaluminum aryloxide derivatives were prepared via the alcoholysis of tricyclopentadienylaluminum with 2,6-di-tertf-butyl-4-methylphenol. Ab initio calculations on model compounds suggest that the pentahapto geometry of the cyclopentadienyl ring is due to the electron-withdrawing nature of the aryloxide ligands which allows greater pi-interaction between the aluminum center and the cyclopentadienyl ligand.

Investigations of the novel hetero Diels-Alder reactions between D-mannose-derived halonitroso compouns and cyclopentadiene were conducted. Results demonstrate that the diastereoselectivity of the hetero Diels-Alder reaction between D-mannose-derived halonitroso compound and cyclopentadiene was lower than what was originally expected based on related studies with cyclohexadiene.

Research was conducted to examine facial selectivities in the Diels-Alder reactions of five-substituted 1,3-cyclopentadienes with various dienophiles using ab initio calculations. The examination leads to an explanation of the facial selectivity in the reactions of cyclopentadienes that is consistent with all the experimental evidence. Results demonstrate that calculations at the HF/6-31G* level can be reliably used in probing facial selectivity.

Chemical research using Mossbauer spectral analysis shows that dynamic reorientation of cyclopentadienyl(arene)iron(II) salts of [CpPePhH]+ and [CpFePhMe]+ can be stopped when 0.85 and 1.36 GPa of pressure is applied. Extrapolated quadrupole splitting values at 10(super -4) GPa at room temperature are used to design a simple theoretical model of [CpFePhH]+ cation reorientation.

The key class of organometallic compounds is composed of eta5-cyclopentadienyl transition-metal derivatives. Cyclopentadienes with amino-functionalized side-chains with their lithium and sodium salts can be used for preparing orgamometallic rhodium complexes. Solubility may be a key issue, and this has led to interest in complexes with an ammonio or amino group born on a pendant arm. The basic amino group can facilitate the synthesis of rhodium derivatives of a functionalized cyclopentadienyl.

The Diels-Alder reaction between 2-phenylcyclopentadiene and alpha(methylthio)acrylonitrile has been investigated. Ab initio molecular orbital calculations showed four asynchronous transition structures on the potential energy surface. These correspond to the formation of para/endo, para/exo, meta/endo and meta/exo adducts.

The cyclopentadienyl trifluoroacetates are designated to undergo solvolysis which gives reaction products of elimination, substitution, substitution with allylic and skeletal rearrangement. This study provides the first kinetic data of cyclopentadienyl cation formation which show a strong dependence on solvent polarity. The reactivity of cyclopentadienyl trifluoroacetates is less than those of fluorenyl and indenyl derivatives by a factor of 10 and the big difference maybe due to antiaromaticity.

The facial selectivity of Diels-Alder reactions in series of 1,3-cyclopentadiene derivatives have been examined using different dienophiles. Chlorine, bromine and iodine atoms were planenonsymmetric atoms pitted against hydrogen or methyl at C-5 of the 1,3-cyclopentadiene derivatives. The results showed no correlation between selectivity and reactivity. In the reactions with 4-phenyl-1,2,4-triazoline-3,5-dione as the dienophile, filled repulsion with the halogen substituent was found to influence selectivity in the reactions.

Hydrophobic and hydrogen-bonding effects on the kinetics of Diels-Alder reactions in aqueous solution were investigated. To this end, the reactions of cyclopentadiene (CP) with methyl vinyl ketone (MVK) and with a dienophile, isoprene, were analyzed via Monte Carlo statistical simulations employing a quantum mechanical and molecular mechanical potential. The results, which showed the absence of hydrogen bonding between reactant and solvent in the reaction between CP and isoprene, demonstrated the equal role played by hydrophobic and hydrogen bonding effects in the transition state stabilization in the reaction between CP and MVK.

A new synthetic route to 1,6-anydrohexopyranose-cyclopentadiene adducts is reported. It is based on the Lewis acid-catalyzed rearrangement of a D-glucose-derived alkene, 1,2:5,6-di-O-isopropylidene-3-deoxy-alpha-D-erythro-hex-3-enofuranose, acyclic dienophile and subsequent cycloaddition with cyclopentadiene. Alkenes which lack a diene group, however, reduce to the enone isolevoglucosenone.

The Diels-Alder reactions of (S)S-4a,5,8,8a-tetrahydro-5,8-methane-2-(p-tolysulfinyl)-1,4-napthoquinones with cyclopentadiene are studied to determine the controlling action of the sulfinyl group on the pi-facial diastereo- and endo exo selectivities of sulfinyl dienophiles. The endo/exo selectivity and reactivity are indeed influenced by the sulfinyl group with the formation of either exo-anti-endo or endo-anti-endo bisadducts, depending on the conditions employed.

The structure and asymmetric Diels-Alder reaction of allene-1,3-dicarboxylates with cyclopentadiene were determined towards pi-face selective reactions due to the axial asymmetry of the allene moiety. The reactions afforded endo adducts formed by the easy access of the diene and the dienophile. The favorable approach is indeed provided by the axial asymmetry of the allene moiety and the secondary optical interaction.

Endo/exo and diastereofacial selectivities are observed during the Diels-Alder reactions of chiral butenolides with cyclopentadiene. A basis set with polarization functions is applied to obtain an ideal selectivity. Low energy barrier is involved in the generation of endo adducts compared to the exo products. The sterically favorable anti products are diastereoselectively formed with respect to the syn adducts. The butenolides reacting are crotonolactone and beta-angelica.

A new pathway to 1,5-di-tert-butyl-1,3-cyclopentadiene is introduced. The new procedure starts with the preparation of 1,2-di-tert-butylcyclopentene via the reaction of olefin 2,2,8,8-tetramethylnonane-3,7-dione under McMurry coupling conditions. The olefin is epoxidized to 1,2-di-tert-butylcyclopentenen oxide which is converted to the final product via direct dehydration. The endo-selective Diels-Alder dimerization of the final product is also discussed.

Ab initio calculations concerning the chemistry and activation energy of the Diels-Alder and Staudinger reactions between ketene and cyclopentadiene were carried out. According to the results, which were in good agreement with experimental observations, the Diels-Alder reaction occurs simultaneously unlike the Staudinger reaction which occurs sequentially. The cycloadditions were also found to be exothermic, kinetically controlled reactions that produce cyclobutanone exclusively.

The cyclization of 1,3-cis-5-hexatriene to 1,3-cyclohexadiene is accelerated by the complexation of Lithium cation. These electrostatic accelerations are due to higher electrostatic stabilization of the transition structure than the ground state. The electrostatic acceleration effect of the 1,5-hydrogen shift in cyclopentadiene is also generated by the complexation of Na+, Mg2+, HBe+ and Be2+. The acceleration is maximum with Be2+ and minimum with Na+.

The Diels-Alder dimerizations of several substituted cyclopentadienes were investigated within a theoretical and an experimental framework. Specifically, ab initio calculations and geometrical modeling were conducted at the 6-31G(d) SCF level on the cyclopentadiene monomer, endo dimer, endo transition state, exo dimer, exo transition state and the spiro(2.4)hepta-4,6-diene monomer and other compounds. The Diels-Alder dimer with two adducts formed rapidly after preparation of 1-oxaspiro(2.4)hepta-4,6-diene. Similar results were obtained when two substituted spiroheptadienes were used to replace 1-oxaspiro(2.4)hepta-4,6-diene.

Diels-Alder addition of 3-butenoyls-1,3-oxazolin-2-one to cyclopentadiene subjected to catalytic amounts of dichloro-Ti complexes of alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOLs) is investigated. The investigation reveals that the Ti-BINOLate- and Ti-TADDOLate mediated reactions of electrophiles having nucleophiles is identical to the reactions associated with the nucleophilic organometallic additions to carbonyl groups.

Several complexes of the type (Cp/Cp*Ru(oligothiophene))PF6, where Cp is eta-5-cyclopentadienyl and Cp* is eta-5-pentamethylcyclopentadienyl, result from reactions between (Cp/Cp*Ru(CH3CN)3)PF6 and the corresponding oligothiophenes. There is an upward and a downward shift in the bound and unbound ring resonances, respectively, when Ru binds to an oligothiophene's thiophene ring. The electronic structure of oligothiophene is affected by Ru to a great extent due to increased inter-ring conjugations.

Diels-Alder addition reaction of cyclopentadiene and 1,4-diacetoxy-2-butyne in the absence of a catalyst and at slightly elevated temperature and pressure leads to the formation of 2,3-bis(acetoxymethyl)bicyclo (2.2.1)hepta-2,5-diene, a polyfunctional bicyclic compound. The ability of this compound to serve as a substrate in several reactions is confirmed by subjecting it to palladium-catalyzed elimination, which yields the corresponding vinylic acetate.

Reaction between sulfur transfer reagents RSphth and CpRu(PPh3)(CO)SH produces CpRu(PPh3)(CO)SSR complexes having disulfanido ligands. Reaction of disulfur transfer reagents RSSphth with CpRu((PPh)3)(CO)SH produces complexes CpRu(PPh3)(CO)SSR having trisulfinado ligands. X-ray diffraction studies help determine the structures of both types of complexes. The complexes do not undergo facile desulfurization.

Analysis of the Diels-Alder (DA) reaction between cyclopentadiene and 5-substituted-1,4-naphthoquinones and methyl vinyl ketone in water reveals a high reaction rate due to simultaneous hydrophobic destabilization of initial state and stabilization of activated complex by hydrogen bonding to the dienophile. Analysis of substituent effects on reaction rate in different solvents shows that polarity of activated complex in water is the same as that in other solvents.

Ab initio calculations of the reactions of ethyne with cyclopentadiene and ethyne with 1H-, 2H- and 3H-phosphole help determine activation energies of the reactions. The calculated activation energy, geometry and electron distribution suggest a concerted (4+2) cycloaddition pathway for all the reactions. The studies support the mechanism proposed by Mathey for reactions between substituted 1H-phosphole and alkynes.

An analysis of the thermal rearrangements of five 5-alkyl-1,2,3,4,5-pentakis(methoxy carbonyl)-cyclopentadienes in methanol reveals that four cyclopentadiene systems dissociate into ion pairs due to C-C bond heterolysis. Benzyl cyclopentadiene rearranges through a concerted mechanism that involves methoxycarbonyl migration. The other four cyclopentadienes contain benzhydryl, methoxymethyl, 1-adamantyl and p-methoxybenzyl alkyl groups respectively.

The pentaisopropylcyclopentadienyl radical (1) was characterized using EPR/ENDOR, proton NMR spectroscopy and mass spectrometry. Yellow-green crystals of 1, which is extremely air sensitive under formation of tetraisopropylcyclopentadienone, result from the chemical or electrochemical oxidation of pentaisopropylcyclopentadienylsodium. Pentaisopropylcyclopentadienyl chloride (5) or bromide and antimony pentachloride provide the pentaisopropylcyclopentadienyl cation 5.

Different organometallic products can by synthesized by synthons, molybdenum compounds consisting of only halides and a solitary cyclopentadienyl ring, CpMoXn. A compound is prepared in the form of CpMoCl3 by oxidating CpMoCl2 by PhICl2, attenuating CpMoCl4 by TiCl3, or by conproptionating CpMoCl2 and CpMoCl4. CpMoX3 materials are most suitably synthesized by a decarboxylation process due to the possible rapidity in synthesis of CpMoCl3 when CpMoCl3(CO)2 is subjected to a process of decarboxylation.

The chemistry of pyrroles and phosphole are examined computationally. The analytical examination of 2H- and 3H-pyrroles reveal interconversion, which is proved by the close energy levels of the two, with an obstacle of 26.3 kcal mol (-1). A low barrier of 16.0 kcal mol (-1) is observed in the process of transforming 1H-phosphole to a 2H-phosphole. The conformation and electron density diffusions of various transition states, through which the (1,5) hydrogen translocation of cyclopentadiene, pyrrole, and phosphole take place, resemble one another. A concerted (1,5) hydrogen shift is observed as the common mechanism for all the migrations by this deduction.

A technique for coupling cyclopentadienyl groups to the napthalene nucleus was developed, using the reaction of cyclopentadienylcopper dimethyl sulfide with 1,8-diiodonapthalene. The Diels-Alder adduct is produced from the coupling of two such peri positions on the napthalene from the initial 1-iodo-8-(5-cyclopentadienyl)-napthalene. The Diels-Alder adduct is formed by the break down of 1-(1-cyclopentadienyl)-8-(5-cyclopentadienyl) napthalene which is formed by the 1, 8-di(5-cyclopentadienyl)-napthalne, experiencing a single sigmatropic hydrogen shift.

A newly suggested quantum chemical approach for ab initio computations of dynamic electron correlation influences in molecular systems aimed to theoretically examine the lowest valence and Rydberg excited states of cyclopentadiene, furan and pyrrole. These valence excited singlet states and the 1a2 leads to 3s, 3p and 3d Rydberg states for cyclopentadiene and furan were included. The valence excited states 1A (sub 1) (super +) (7.89, 7.46, 7.74 eV) and 1B2 (5.27, 5.92, 6.04 eV) induced the two primary characteristics in the spectra. The results are consistent with experimental findings but vary dramatically from earlier theoretical predictions.

The reaction of the electrophilic Cp*Ru+ fragment with steroids results in C-O, C-H and C-C bond activation that leads to aromatization of the A-ring and elimintion of CH4, H2 and H2O or of CH4. With testosterone and progesterone, the reactions proceed via a hydridocyclohexadienyl intermediate while those with cholesterol and dehydroisoandrosterone go through a triene intermediate. Trapping of the triene with sodium methoxide leads to MeO addition at C6. With prednisolone, excess Cp*Ry+ causes fragmentation of the steroid.

Ab initio calculations are reported for the reactions of cyclopentadiene with five dienophiles. Geometry optimizations were made with a 6-31G* basis set and correlation energies were computed to the MP3 level. Results showed that these calculations may be used in the prediction of relative reactivities for typical Diels-Alder reactions. However, a constant discrepancy of 8 cal/mol.K for computed and observed entropies of activation suggest that the transition-state structures are too product-like at this level. The results for isoprene and methyl vinyl ketone reflect a greater reactivity for the s-cis forms of conjugated dienophiles.

An experiment which aims to simulate nature's way of synthesizing pure enatiomers which uses well-defined enzymes is discussed. The enzymes pick up racemic or prochiral substrates which are eventually converted into pure enantiomers by highly diastereoselective methods. It is recognized that the Diels-Alder cycloadditions play a vital role in the enantioselective synthesis of homochiral 4pi-systems.