Juho Helaja

Cycloisomerization of 2-alkynylanilines to indoles catalyzed by carbon-supported gold nanoparticles and subsequent homocoupling to 3,3'-biindoles.

However, the reductive nature of those conditions limited thereaction scope and precluded the possibility of furthercascade functionalization. Soon after, Somorjai, Toste, andco-workers reported that Pt nanoparticles supported onmesoporous silica are able to efficiently promote the intra-molecular heterocyclization of N-carbamate protected 2-alkynylanilinestoaffordthecorrespondingindoleproductsinexcellent yields.

Noncovalent attachment of pyro-pheophorbide a to a carbon nanotube

Pyrene mediated noncovalent attachment of a chlorophyll derivative, pyro-pheophorbide a, to a soluble single wall carbon nanotube is reported and the resultant CD, UV-Vis absorbance, fluorescence and 1H NMR spectra are discussed.

Isolation of a zwitterionic dienegold(III) complex intermediate in the direct conversion of enyne-amines to cyclopentadienes.

Gold-mediated homogeneous catalysis has shown, recently, its power, uniqueness, and versatility especially in electrophilic activation of alkynes for nucleophilic attack. Cycloisomerization of enynes, and other alkynes carrying nucleophilic groups represents a large category in gold mediated catalysis. Due to the fact that this chemistry is in its infancy, only a few mechanistic studies have been reported. 2] The recent findings in gold and other late transition-metal catalysis have provided effective alternatives to classical Pauson–Khand cyclocarbonylation and the Nazarov cyclization for the synthesis of cyclopentadienes (Cp). Toste et al. have shown that the cationic Au species Ph3PAuCl/ AgSbF6 catalyses the cycloisomerazation of 1,2,4-triene (enallene; 2) to cyclopentadiene (Cp; 3 ; Scheme 1) with high yields and turnover numbers. In line with these findings, Iwasawa et al. have shown that the same conversion can be catalyzed by PtCl2 with equal performance. [6] An evident restriction in these methods is that the synthesis of the prerequisite starting material (allenes) proceeds in many cases with modest or low yields when traditional methods are applied. Nevertheless, Che s group has recently introduced a facile method to access (asymmetric) allenes, 2, from aminoalkynes, 1, either by KAuCl4 or AgNO3 catalysis. Inspired by these achievements we set out to investigate the possibility of a direct conversion of enyne–amine 1 to Cp 3, thus reducing a two-step sequence (synthesis of allene followed by cycloisomerization) to a single catalytic event. For the gold-catalyzed allene formation from propargylamines, deuterium labeling experiments have proven that a 1,5-hydride migration from the amine moiety controls the progress and direction of the reaction (Scheme 2). For systems in which intramolecular migrations occur by other nucleophiles than hydride, there are examples showing how the migration mode, and therefore the direction of reaction can be controlled, for example by the choice of cationic Au or neutral AuACHTUNGTRENNUNG(I/III) catalysts, as well as by slight modifications of the substrate. These two factors can both have a

Effect of mutual position of electron donor and acceptor on photoinduced electron transfer in supramolecular chlorophyll-fullerene dyads.

In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C60 electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13(4) or 17(4) position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C60. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor-acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.

Biomimetic zinc chlorin–poly(4-vinylpyridine) assemblies: doping level dependent emission–absorption regimes

To develop biomimetic dye–polymers for photonics, two different types of Zn chlorin–poly(4-vinylpyridine) (P4VP) assemblies were prepared by varying Zn pyro-pheophorbide a methylester (ZnPPME) and Zn 31-OH-pyro-pheophorbide a methylester (Zn-31-OH-PPME) doping levels. 1H NMR spectroscopy and diffusion ordered NMR spectroscopy (DOSY) studies revealed that a coordinative interaction between Zn chlorin and P4VP was predominant in solution (d5-nitrobenzene). Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) characterization of bulk samples of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) doped with variable amounts of Zn chlorin showed that the pigment doping transformed the native cylindrical block copolymer nanostructures to lamellar morphologies. The result indicates that the pyridine moiety–Zn chlorin coordination is stronger than the aggregation tendency between the pigment molecules even in the solid state. UV-Vis absorption spectroscopy studies of a Zn chlorin–P4VP thin film showed characteristic monomeric chlorin spectra, while steady-state fluorescence spectroscopy displayed quenching of fluorescence and time-resolved studies indicated shortening of fluorescence lifetimes with an increasing chlorin doping level. Notably, time-resolved fluorescence spectroscopy revealed that the lifetime decay changed from monoexponential to biexponential above 0.5 wt% (ca. 0.001 equiv.) loadings. The Forster analysis implies that excitonic chlorin–chlorin interactions are observed in the thin films when the distance between the pigment molecules is approximately 50 A. The Zn chlorin–P4VP solid films emit strongly up to 1 wt% (ca. 0.002 equiv.) doping level above which the chlorin–chlorin interactions start to linearly dominate with an increase of doping level, while with 10 wt% (ca. 0.02 equiv.) loading less than 10% of fluorescence remains. Doping levels up to 300 wt% (0.5 equiv.) can be used in absorbing materials without the formation of chlorin aggregates. These defined optical response regions pave the way for photonic materials based on biopigment assemblies.

Tautomeric Switching and Metal‐Cation Sensing of Ligand‐Equipped 4‐Hydroxy‐/4‐oxo‐1,4‐dihydroquinolines

Novel 4-hydroxyquinoline (4HQ) based tautomeric switches are reported. 4HQs equipped with coordinative side arms (8-arylimino and 3-piperidin-1-ylmethyl groups) were synthesized to access O- or N-selective chelation of Zn(2+) and Cd(2+) ions by 4HQ. In the case of the monodentate arylimino group, O chelation of metal ions induces concomitant switching of phenol tautomer to the keto form in nonpolar or aprotic media. This change is accompanied by selective and highly sensitive fluorometric sensing of Zn(2+) ions. In the case of the bidentate 8-(quinolin-8-ylimino)methyl side arm, NMR studies in CD(3) OD indicated that both Cd(2+) and Zn(2+) ions afford N chelation for 4HQ, coexisting with tautomeric switching from quinolin-4(1H)-one to quinolin-4-olate. In corroboration, UV/Vis-monitored metal-ion titrations in toluene and methanol implied similar structural changes. Additionally, fluorescence measurements indicated that the metal-triggered tautomeric switching is associated with compound signaling properties. The results are supported by DFT calculations at the B3LYP 6-31G* level. Several X-ray structures of metal-free and metal-chelating 4HQ are presented to support the solution studies.

Regioselectivity of Intermolecular Pauson–Khand Reaction of Aliphatic Alkynes: Experimental and Theoretical Study of the Effect of Alkyne Polarization

Generally judged poor electronic regioselectivity of alkyne insertion in intermolecular Pauson-Khand reaction (PKR) has severely restricted its synthetic applications. In our previous rational study concerning diarylalkynes (Fager-Jokela, E.; Muuronen, M.; Patzschke, M.; Helaja, J. J. Org. Chem. 2012, 77, 9134-9147), both experimental and theoretical results indicated that purely electronic factors, i.e., alkyne polarization via resonance effect, induced the observed modest regioselectivity. In the present work, we substantiate that the alkyne polarization via inductive effect can result notable, synthetically valuable regioselectivity. Computational study at DFT level was performed to disclose the electronic origin of the selectivity. Overall, the NBO charges of alkynes correlated qualitatively with regioisomer outcome. In a detailed computational PKR case study, the obtained Boltzmann distributions of the transition state (TS) populations correlate closely with experimental regioselectivity. Analysis of the TS-structures revealed that weak interactions, e.g., hydrogen bonding and steric repulsion, affect the regioselectivity and can easily override the electronic guidance.

Interaction of oxygen functionalized alkenes with a methylaluminoxane-zirconocene catalyst studied by NMR

Abstract Reactions of hydroxyl, ether and carbonyl functionalized alkenes with methylaluminoxane prepared in toluene- d 8 (MAO) and zirconocenedichloride (Cp 2 ZrCl 2 ) were investigated by 1 H- and 13 C-NMR spectroscopy at 27°C. The 11 alkenes studied bear a terminal CC bond separated by 7–9 (–CH 2 –) units from the heteroatom moiety. Intramolecular connectivities in mono (alkene), bi (alkene and MAO) and tri (alkene, MAO and Cp 2 ZrCl 2 ) component mixtures were determined by 2D HSQC, HMBC, ROESY and NOESY NMR techniques. The five studied alkenols formed aluminium alkoxides with MAO even in the case of a substantial steric hindrance around the OH group. Zirconocene enhanced the formation of aluminium alkoxides. Decomposition to free alkenol was observed only for the straight chain alkenol (10-undecen-1-ol). The OTMS derivatives formed dimers of the type CH 2 CR 1 R 2 along with methyl derivatives, CH 2 C(Me)(R) and (Me)CHCH(R), in the presence of MAO and Cp 2 ZrCl 2 . 10-Undecenyl methyl ether and methyl decenoate remained mainly as a free comonomer in the presence of MAO or MAO/Cp 2 ZrCl 2 , though a transient coordination of the former to MAO was deduced. Unsaturated species Me 2 CCH–Al–X and CH 2 CH(CH 2 ) 5 CH 2 CHC( t -Bu)O–Al–X (X=MAO oligomer) were formed in the reaction of t -butyl undecenoate or 2,2-dimethyl-11-dodecen-3-one with MAO or MAO/Cp 2 ZrCl 2 . Interaction of the CH 2 CH part of the functionalized alkenes with zirconocene was not observed. A possible coordination of the CC bond to MAO was observed only for the sec alkenols.

An unexpected allomer of chlorophyll: 132(S)-hydroxy-10-methoxychlorophyll b

Abstract The allomerization of chlorophyll b in methanol produced 13 2 ( S )-hydroxy-10-methoxychlorophyll b in a yield of ca. 8%. The formation of this allomer was totally unexpected, as 10-substituted chlorophylls have never been reported before. The structure of the new chlorophyll b derivative was determined on the basis of UV/Vis, FAB-MS, 1 H NMR and 2D ROESY NMR spectra. This letter focuses on the NMR analysis.

Novel Model Compounds for Photoinduced Electron Transfer: Structures of the Folded Conformers of Zinc(II)–Pyropheophytin– Anthraquinone Dyads

The solution structures of the P4‐epimers of Zn(II)–pyropheophytin–anthraquinone dyads (ZnPQ1 and ZnPQ2) were determined using two‐dimensional NMR spectroscopy and molecular modeling. The mutual orientation of the anthraquinone and Zn–pyropheophytin rings was found to be different in the two P4‐epimeric dyads on the basis of the ROESY correlations, observed between the quinone and phorbin protons. The anthraquinone ring is situated below the phorbin macrocycle in both dyads, ZnPQ1 and ZnPQ2. In ZnPQ1, the ring planes show tilting, the anthraquinone ring being in a sloping position below subrings B, C and E of the phorbin macrocycle. In ZnPQ2, the two π‐systems are almost parallel with the anthraquinone ring being located approximately below the center of the phorbin macrocycle.