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Synthesis of novel tetrakis-(N-pyrrolyl)methane was carried out. Reaction mechanism was discussed and structure of novel product was determined by X-ray crystallography. The structural motif C(NR2)4 is rare in chemistry. The formation, NMR spectroscopic characteristics, and X-ray structure are reported for a structurally interesting member of this family, namely tetrakis-(N-pyrrolyl)methane.

The reaction of ninhydrin with ester-activated cyclobutene epoxide (CE-1) containing the fused 1, 4- dimethoxynaphthalene (DMN) chromophore, gave adducts formed by 1, 3-dipolar cycloaddition at the central (C2)-CO (major) and the outer (C1, 3)-CO (minor) positions. Conversion of the minor adduct to quinoxalines (QIN) by reaction with o-phenylenediamines at the a-dione moiety, albeit in poor yield, led to spiro-DMN-1, 4s-QIN dyad in which the plane of the chromophore was orthogonally orientated yet angled to the plane of the DMN chromophore. Reaction of ninhydrin with o-phenylenediamines yielded the corresponding 11-oxoindeno[1, 2-b]quinoxalines which were coupled with CE-BLOCKs to form spiro adducts by reaction at the carbonyl site ; the product from CE-1 was identical with that formed above. Another class of spiro-fused dyads was produced by reaction of ninhydrin with a primary amine followed by cycloaddition of CE-BLOCKs at the carbonyl site, where the amine was available to deliver one chromophore and the CE-BLOCK another.

A new class of container molecules is described and the first steps in producing protypes are reported. Central to the approach is the formation of polynorbornanes with cyclobutene-1, 2-difurfuryl esters at the terminus or similar functionality at the bridgehead of a central norbornane subunit. The synthesis of the furfuryl starting materials is described as well as their anthracenyl counterparts. Conversion to the container systems involved the intermolecular linking of the furfuryl or anthracene by treatment with dimethyl acetylene dicarboxylate (DMAD) in a Diels–Alder (DA) protocol under thermal or high-pressure (HP) conditions. In practice, no intermolecular linking occurred between the norbornane substrates and only products from DA 1:1-addition with DMAD were produced. Intramolecular addition of one of the furfuryl units onto the cyclobutene p-bond was detected under HP conditions, and this intermolecular product was capable of isolation and characterization by working at room temperature or below, but reverted to starting material above room temperature. When conducted in the presence of DMAD, a single 1:1-adduct was obtained in which one furfuryl moiety was intramolecularly cyclized and the other present as the DMAD adduct ; again this product underwent retro-DA reaction at 40 C. Similar intermolecular cyclization was observed with the bis-anthracenyl esters. The stereoselectivity of the intermolecular attack of the furfuryl diene with the dienophilic cyclobutene gave a single adduct by endo-face attack in which the oxa-bridge is endo-positioned. Quantum chemical DFT calculations (B3LYP) predict that the formation of the endo-isomer is kinetically favored and that relief of ring strain enhances the rate of retro-Diels–Alder in the tethered system.

Norbornadiene cycloadducts have been reacted with 3, 6-di(2-pyridyl)-s-tetrazine to produce pyridazines 14, 16, 18 (diene protected alkenes), following dehydrogenation (DDQ) of the intermediate dihydropyridazines. The title 3, 6-di(2-pyridyl)-pyridazinonorbornadiene 3 was produced under flash vacuum pyrolysis conditions by ejection of anthracene from 14 (590 oC), isobenzofuran 16 (630 oC) or isoindole 18 (580 oC) establishing isoindole > anthracene > isobenzofuran dienofugacity order. Calculations of the respective retro Diels-alder activation energies at the B3LYP/6-31G* level of theory correctly predicted the experimentally found isobenzofuran> anthracene>isoindole order. Cavity bis-3, 6-di(2-pyridyl)-pyridazine (dppn) and chevron-shaped bis-dppn ligands were prepared from 3 by coupling at the norbornene pi-bond.

Donor-acceptor interactions within fullerene-porphyrin architectures are important for multi-component model systems designed for transmission and process of solar energy. Most of these supramolecular photocurrent-generating devices are based on covalently linked components using fullerenes and porphyrins. The alternative approach is the use of self-assembled supramolecular donor-acceptor (D-A) model systems obtained by metal complexation. . , Here we report computational study of a novel bis-porphyrin-fullerene supramolecular complex 1@C60add designed for photovoltaic devices using quantum-chemical calculations. The study of the electronic properties of the excited states of 1@C60add complex indicates electron transfer from porphyrin to fullerene moiety. In continuation, porphyrin-fullerene supramolecular system 1@C60add was synthetized by self-assembly of bisporphyrin component 1 and C60add and its photophysical properties studied, showing large fluorescence quenching by fullerene moiety.

A computational study of a series of space separated bis-porphyrin “ molecular tweezers” 1 using the AM1 method has been conducted (Figure 1).[1, 2] It was found that bis-porphyrin systems possessing polycyclic spacers are significantly less rigid than previously thought.[3, 4] Variation of the metal-metal separation distance does not cause a significant energy change thus enabling these molecules to easily adjust to the optimal bonding distance required for complexation of various pyridyl ligands. Binding energies for a series of guests were estimated and indicated that the preferred complexation occurs within the cavity of these molecular tweezers (selective binding). With a help of molecular design, bis-porphyrin 1, having a more flexible framework incorporating two “ molecular hinges” was synthetised. Its complexation with several bis-pyridyl guests was studied by NMR and UV spectroscopy.

A computational study of a series of space separated bis-porphyrin “ molecular tweezers” using the AM1 method has been conducted. It was found that bis-porphyrin systems possessing polycyclic spacers are significantly less rigid than previously thought. Variation of the metal-metal separation distance does not cause a significant energy change thus enabling these molecules to easily adjust to the optimal bonding distance required for complexation of various pyridyl ligands. Binding energies for a series of guests were estimated and indicated that the preferred complexation occurs within the cavity of these molecular tweezers (selective binding). By molecular design, bis-porphyrin 1, having a more flexible framework incorporating two “ molecular hinges” was synthetised. Its complexation with bis-pyridyl guests was studied by NMR and UV spectroscopy.

Dimethyl-3, 3a, 3b, 4, 6a, 7a-hexahydro-3, 4, 7-metheno-7H-cyclopenta[a] pentalene-7, 8-dicarboxylate (3, a 9, 10-dihydrofulvalene pincer cycloadduct) was found to be a versatile building block for the synthesis of polynorbornyl scaffolds containing various end functionalities such as porphyrins, pyrimidine, and the phenanthroline ligand in the free and complexed forms. The block is stable under various cycloaddition reaction conditions and has high ?-bond reactivity. Molecular modelling using a semi-empirical based method (AM1) shows that incorporation of this diene block into polynorbornyl systems has an important influence on their overall architecture. In particular, incorporation of the block results in a straightening of the curvature normally observed in polynorbornyl molecules to form almost ideally linear polycyclic rigid spacers.

In this paper, semiempirical study of a series of space separated bis-porphyrin "molecular tweezers" using AM1 method were presented. It was found that bis-porphyrine systems such as 2 are significantly less rigid than previously thought. Variation of metal-metal separation distance does not cause significant energy change thus enabling these molecules to easily adjust to the optimal bonding distance required for complexation of various pyridyl ligands.

Computational study of decarbonylation of 7-norbornenones was employed in order to rationalize experimental results. It was found that activation barriers of these cheletropic reactions depend on the structures of 7-norbornenones and products obtained after decarbonylation.

1, 3-dipolar cycloreversion of cyclobutane triazolines was found to be the key step of novel heterocyclic rearrangement.

In this paper 1, 3-dipolar cycloaddition reactions of 5, 10, 15, 20-tetra-(3, 5-di(tert-butyl)phenyl)porphyrin-2, 3-dione with acetylene cyclobutene epoxide were described. This reaction offers new synthetic approach to formation of dyads having functional group at each termini of policyclic rigid framework.

Thermal isomerisation of the strained cyclobutane diester triazoline led to the formation of the product possessing a novel 1, 2, 7-triaza-[3.3.0]octa-2-ene ring system incorporated in a norbornane framework. Experimental evidence and quantum chemical calculations (semiempirical and DFT) have been used to support a postulated reaction mechanism involving as the first step, a rare example of intramolecular 1, 3-dipolar cycloreversion. Subsequently, several steps involving 1, 3-dipolar ring closure, [1, 3]hydrogen-shifts and an intramolecular addition are postulated leading to the observed product of this deep-seated isomerization. The influence of changing substituents on the product outcome of this novel reaction cascade was also studied.

Ab initio (RHF/3-21G and RHF/6-31G* basis sets) and semiempirical (AM1 and PM3) quantum chemical calculations have been applied to a study of Diels-Alder reactions of furan and cyclopentadiene as 1, 3-dienes, with norbornene and 7-oxanorbornene as dienophiles, in order to model  -facial selectivities and stereoselectivities of these reactions. To achieve this goal, transition states for these reactions are located and activation energies estimated. The exclusive exo- pi- facial selectivity exhibited in these cycloadditions are readily predicted using semiempirical or ab initio methods. To determine stereochemical outcomes following pi-facial attack, ab initio calculations are required. Exo, endo- stereoselectivities found experimentally, are successfully predicted by using RHF/6-31G*//3-21G or higher levels of calculations. Secondary orbital interactions are postulated to be responsible for the experimental stereoselectivities.

In this paper, reactions of substituted 1, 2, 4-triazines with norbornenes and 7-oxanorbornenes are described. Depending on the substrate and the reaction conditions, 1:1 or 2:1 deazetized cycloaddition products were obtained. Furthermore, a novel aza-isobenzofuran was prepared as an intermediate by flash vacuum pyrolysis of one on these adducts.

Succinimide-functionalized N, O-, N, C-, and N, N-bridged benzo[ 2] polynorbornanes ( benzosesquinorbornadienes) are reported for the first time and are prepared by the cycloaddition of either five-membered cyclic 1, 3-dienes onto N-substituted benzo-7-azanorbornadienomaleimides or N-substituted isoindoles onto the appropriate norbornadienomaleimides. These products contain an end-fused norbornene ( or a 7-substituted relative) and have been designed to act as alkene BLOCKs for the production of nano-scaffolds with up to six addressable sites supplied by each norbornene unit. The N-bridges in these BLOCKs ( and their coupled products) allow N-substituent mobility by invertomerization of the sp(3) nitrogen whereas the N-substituents on the succinimides are attached to an sp(2) nitrogen atom and remain static. Preferred invertomer geometry can be determined using molecular modelling.

Density functional theory (B3LYP/6-31G*) was used to study a series of homosesquinorbornenes and sesquibicyclo[2.2.2]octenes. The compounds in which the two faces of the double bond are different are predicted to have a pyramidal double bond with butterfly bendings ranging from 1.8 to 17.9 degs. The degree of pyramidalization of these central double bonds is greater in the homosesquinorbornenes than in the sesquibicyclo[2.2.2]octenes.

Mechanism of the thermal rearrangement of several triazoline derivatives was investigated.

Thiophene has been reacted under high-pressure and temperature with N-methylmaleimide and N-phenylmaleimide to produce Diels-Alder exo- and endo-adducts. Reaction of 7-oxanorbornadiene-2, 3-dicarboxylic anhydride, a highly reactive dienophile, with thiophene occurred under high-pressure even at room temperature to yield stereoisomeric 1:1-adducts by site selective attack at the maleic anhydride type of pi-bond. This approach afforded the first examples of syn- and anti- heterobridged sesquinorbornadienes containing a sulfur bridge. Similar reaction of isobenzothiophene was even more facile as reaction occurred at room temperature and atmospheric pressure to yield its benzoanalogues. Thermal fragmentation involving loss of furan and sulfur occurred from both classes of adducts under FVP conditions (370 0C, 0.005 mbar) to produce phthalic anhydride or naphthalene-2, 3-dicarboxylic anhydride respectively. The putative 7-thianorbornadiene intermediates, generated by loss of furan, were not detected. Reaction of exo-N-methyl 7-thianorbornene-5, 6-succinimide with the ester-activated cyclobutenoaziridine provided access to CNS-[3]polynorbornane, while similar addition of the exo, endo-isomer of O, S-benzosesquinorbornadiene afforded the CNOS-[4]polynorbornane. These are the first S-bridged [n]polynorbornanes to be reported and their cycloaddition reactions will be also reported.

This paper announces the results of certain 1, 3-dipolar cycloadditions to polycyclic aromatic hydrocarbons (PAHs). The 1, 3-dipoles generated from cyclobutene diester epoxides thermally reacted with PAHs to give cycloadducts. This reaction demonstrated the remarkable ability of these 1, 3-dipoles to disrupt an aromatic system by adding across specific ‘ aromatic double bonds’ . Similar products were prepared by “ cross” oxadiazole (OD) coupling yielding the same geometry and stereochemistry as the cyclobutene diester epoxide derived products, but in inferior yields.

4, 7-Di(2-pyridyl)-5, 6-diazaisobenzofuran, the first stable isobenzofuran to contain two ring-nitrogens, has been prepared using the s-tetrazine-induced fragmentation of 5, 8-di(2-pyridyl)-1, 4-epoxy-1, 4-dihydrophthalazine and employed in cycloaddition protocols to form scaffold bis-dppn-ligands having specific molecular architectures.

The N-bridged [n]polynorbornanes were prepared using 1, 3-dipolar cycloaddition reaction involving benzonorbornadienes as the dipolarophile and the 1, 3-dipole formed by the ring-opening of a 5-azabicyclo[2.1.0]pentanes.

Novel photochemistry of cyclobutanotriazolines with N-2-phthalimido-ethyl and N-phenacyl substituents is reported. The main reaction path is fragmentation to an alkene and a triazole, while formation of aziridines by loss of dinitrogen is a minor reaction

High pressure Diels-Alder reaction of furan with 1, 4-epoxynaphthalene has been described and product stereochemistries discussed for the 1:1- and higher order cycloadducts. HP experiments were found to be superior over thermal and microwave cycloadditions, especially in regard to the formation of the higher order products.

RHF/6-31G* calculations, followed by single point energy estimations at the B3LYP/6-31+G**//RHF/6-31G* level were employed in a systematic computational study to estimate gas- phase proton affinities (PA) of selected sesqui- and sester-7-azabicyclo [2.2.1]norbornanes. Our calculations indicate that the basicities of the bridging nitrogen atoms are affected by their incorporation into a bicyclo[2.2.1]heptane framework. Furthermore, proximity effects of intramolecular hydrogen bonding plays an important role to increase basicity of fused 7-azanorbornanes in those cases where there is possibility of nitrogen bound hydrogen to bind to a neighbouring heteroatom at the adjacent 7-norbornane position.

The results of a 1, 3-dipolar cycloaddition reaction involving polyaromatic hydrocarbons (PAHs) as the dipolarophiles and the 1, 3-dipole formed by the ring-opening of a 5-oxabicyclo[2.1.0]pentane are reported. PAHs such as naphthalene, anthracene, benzanthracene, acenaphthene, phenanthrene, 9, 10-phenanthroline, gave mixtures of endo- (major) and exo- adducts, while fluorenone and anthraquinone yielded adducts across the carbonyl double bond. Only rare examples of cycloaddition reactions where anthracene acts as a dipolarophile are reported in literature