Walter Frank

Three-Component Synthesis of N-Boc-4-iodopyrroles and Sequential One-Pot Alkynylation∥

(Hetero)aryl-, alkenyl-, and selected alkyl-substituted acid chlorides can be efficiently coupled with N-Boc-protected propargylamine to produce ynones which are converted in a one-pot fashion to 2-substituted N-Boc-4-iodopyrroles. Upon addition of a further alkyne, another Sonogashira coupling can be carried out in a one-pot fashion. This sequentially Pd/Cu-catalyzed process represents a very mild and efficient entry to 2,4-disubstituted N-Boc-pyrroles.

Expanding the Chemistry of Cationic N-Heterocyclic Carbenes: Alternative Synthesis, Reactivity, and Coordination Chemistry

A new synthetic route to complexes of the cationic N-heterocyclic carbene ligand 2 has been developed by the attachment of a cationic pentamethylcyclopentadienylruthenium ([RuCp*](+)) fragment to a metal-coordinated benzimidazol-2-ylidene ligand. The coordination chemistry and the steric and electronic properties of the cationic carbene were investigated in detail by experimental and theoretical methods. X-ray structures of three carbene-metal complexes were determined. The cationic ligand 2 is a poorer overall electron donor relative to the related neutral carbene, which is evident from cyclic voltammetry (CV) and IR measurements.

Schwermetall-π-Komplexe. XI. Synthese, Struktur und thermisches Verhalten von Bis(1,2,4-trimethylbenzol)thallium(I)-tetrachloroaluminat bzw. −gallat — Zum einfluβ des gegenions auf struktur und stabilität eines kationischen Bis(aren) hauptgruppenmetallkomplexes☆

Bis(1,2,4-trimethylbenzene)thallium(+1) tetrachloroaluminate(+3) (1) has been prepared from 1,2,4-trimethylbenzen, thallium(I) chloride and aluminium trichloride. In an analogous reaction with gallium trichloride, bis(1,2,4-trimethylbenzene)thallium(+1) tetrachlorogallate(+3) (2) was obtained. The colourless compounds crystallize isotypically in the triclinic space group P1 (1: a = 9.525(2) A, b = 10.903(2) A, c = 11.972(2) A, α = 102.39(2)°, β = 90.29(1)°, γ = 107.96(1)° at T = −90 ± 1°C; 2: a = 9.585(2) A, b = 10.923(2) A, c = 11.966(2) A, α = 102.18(2)°, β = 90.66(2)°, γ = 107.74(2)° at T = −90 ± 1° C; Z = 2). In the solid state the compounds can be described as dimeric thallium(I) tetrachlorometallates with a skeleton similar to that of (TeI4)4, shielded by four arenes coordinated in pairs at the thallium atoms. The complete ‘molecules’ have point group symmetry 1. According to DTA measurements, the compounds loose all the coordinated arenes simultaneously, 1 at 59°C and 2 at 51°C, yielding pure thallium(+1) tetrachlorometallates. The different thermal stability, the mean TlC(arene) bond lengths and indirectly the corresponding TlCl bond lengths show the thallium-arene π-bonding to be significantly weaker in the gallate 2 than in the aluminate 1.

Stickstoffverbindungen von elementen der dritten hauptgruppe mit intra- und intermolekularen donor-akzeptor-bindungen: IV. Polycyclische alumina-, lithia-, magnesia- und sodia-silazane☆

Die Lewis-aciden Elemente Li, Na, Mg und Al lassen sich leicht in cyclische Strukturen einbauen, die als gemeinsames Molekulfragment die Einheit Me2Si-(NtBu)2 besitzen: Die Rontgenstrukturanalysen an [Me2Si(NtBu)2Mg·THF]2 (II) und [Me2Si(N(tBu)AlMe2)(N(tBu)MgI)]2 (X) weisen die Verbindungen als Dimere aus. Im Falle von II sind zwei SiN2Mg-Vierringe wechselseitig uber N-Mg-Bindungen verbunden, so dass ein dritter N2Mg2-Vierring mit der Punktsymmetrie Ci ( ) entsteht. Das Magnesiumatom ist vierfach koordiniert mit drei unterschiedlichen Mg---N-Bindungslangen (199.3(4), 211.2(4) und 218.8(4) pm) und einer Mg---O-Bindung von 204.9(6) pm zu einem Sauerstoffatom eines koordinierten Tetrahydrofurans. In X bedingen I---Mg-Wechselwirkungen die Ausbildung eines Dimeren mit einem zentrosymmetrischen Mg2I2-Rechteck. Das Magnesiumatom hat als weitere Liganden zwei Stickstoffatome in Abstanden Mg---N 225.9(6) und 229.9(6) pm und eine Methylgruppe in einer Entfernung von 261(1) pm. Das herausragende Strukturmerkmal ist eine N(Mg,Al,Si)N-Bipyramide, die auf intramolekulare Zwei-Zentren- und Donor-Akzeptor-Bindungen zuruckgeht (Al---N 187.7(6) und 188.6(6) pm, Si---N 180.6(5) und 181.0(6) pm). Die drei Nachbarelemente des Periodensystems Mg, Al und Si sind auf diese Art und Weise an ein gemeinsames Stickstoffatom gebunden, das als weiteren Liganden eine t-Butylgruppe besitzt. Es konnten Derivate zu X erhalten werden, die monomer vorliegen: Me2Si(N(tBu)AlMe2)-(N(2Bu)MgR) R = Me, Bz, 2Bu, Ph. Als Vorstufe zu diesen Verbindungen lasst sich die Lithiumvrbindung Me2Si(N(tBu)AlMe2(N(tBu)Li) und das entsprechende Natriumderivat isolieren. Aus dem 1H-NMR-Spektrum folgt abermals eine bi-pyramidale N(Li,Al,Si)N-Anordnung als Grundgerust des Molekuls.

Stickstoffverbindungen von elementen der dritten hauptgruppe mit intra- und intermolekularen donor—akzeptor-bindungen: II. Strukturelle untersuchungen

Abstract The crystal and molecular structures of the three compounds Me 2 Si(N t Bu) 2 (AlPh 2 ) 2 (I), Me 2 Si(N t Bu)(N t BuH)AlCl 2 (II) and [Me 2 Si(N t Bu) 2 InMe] 2 (III) have been obtained by X-ray structure determinations. Compound I represents a bicyclic organometallic molecule, in which two four-membered cycles share a common AlN edge (197.5(6) pm). One of the rings consists of a tetravalent silicon atom, a three-valent nitrogen atom, and an aluminum and nitrogen atom with a four-fold coordination, the other ring unites the two latter atoms together with a tetrahedral aluminum and carbon atom. The carbon atom is a member of a phenyl group and is in a special binding position. One of the aluminum atoms in I is thus stabilized by a donor—acceptor bond, the other by a two-electron-three-center-bond (AlC 214.5(8) and 220.7(5) pm). By temperature dependent NMR techniques it can be shown that molecules such as I show fluctional behaviour in non-polar solvents. In molecule II an intramolecular nitrogen—aluminum bond (199.4(2) pm) is responsible for the formation of a cycle, which contains a tetrahedral silicon atom, two nitrogen atoms (four- and three-fold coordination) and an aluminum atom with four ligands. In the crystal of II hydrogen bonds of the type NH ⋯ Cl can be recognized. The indium compound III (point symmetry, C i ( 1 )) may be described as a polycyclic unit built up of three four-membered rings standing orthogonally against each other and sharing common edges. It originates from two SiN 2 In cycles which are held together by two Nin donor—acceptor bonds (225.6(4) pm), forming an almost square central N 2 In 2 cycle. As a general feature, intramolecular (II), intermolecular donor—acceptor (III) bonds as well as two-electrons-three-center bonds (I), are used to stabilize the electron-deficiency at the aluminum and indium atoms. The synthesis and the properties of the compound Me 2 Si(N t Bu)(N i Prop)(AlMe 2 ) 2 (IV) are described.

Hybrid Ligands with N‐Heterocyclic Carbene and Chiral Phosphaferrocene Components

N-Heterocyclic carbenes (NHCs) possessing one or two 3,4-dimethylphosphaferrocenyl substituents and either methylene or ethylene alkyl bridges have been prepared. These carbenes turned out to be remarkably stable and were characterized by NMR methods and partly by mass spectrometry. Their molybdenum and ruthenium complexes were examined in order to determine the electronic properties and the coordination behaviour of these chiral PC- and PCP-chelate ligands, which combine a NHC unit as a strong sigma-donor with pi-accepting phosphaferrocene moieties. Crystal structures of one ligand precursor and of three complexes have been determined.

Insertion-coupling-cycloisomerization domino synthesis and cation-induced halochromic fluorescence of 2,4-diarylpyrano[2,3-b]indoles.

2,4-Diarylpyrano[2,3-b]indoles are formed via a Pd-Cu-catalyzed insertion-coupling-cycloisomerization domino reaction in moderate yields. Although the tricyclic systems are nonfluorescent in solution, protonation, quaternation, or complexation with metal ions induces intense green luminescence. Most strikingly, selective halochromic fluorescence of zinc and magnesium over calcium ions classify the title compounds as metal-selective luminescence sensors.

Photochemical reactions of transition metal organyl complexes with olefins Part 10. Light-induced formal [5+2] cycloadditions at manganese

Abstract Tricarbonyl-η 5 -2,4-dimethyl-2,4-pentadien-1-yl-manganese ( 1 ) forms upon UV irradiation in THF at 208 K solvent stabilized dicarbonyl-η 5 -2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese ( 2 ). With butynedioic acid dimethyl ester ( 3 ) and diphenylacetylene ( 5 ) complex 2 yields tricarbonyl-η 5 -1,2-dimethoxycarbonyl-4,6-dimethyl- cyclohepta-2,4-dien-1-yl-manganese ( 4 ) and tricarbonyl-η-4,6-dimethyl-1,2-diphenyl-cyclohepta-2,4-dien-1-yl- manganese ( 6 ) in a formal [5+2] cycloaddition. Addition of carbon monoxide and a 1,4-H shift completes the reaction. Propynoic acid methyl ester ( 7 ) forms the 2:1 adduct dicarbonyl-η 5:2 -1,3-dimethyl-6-methoxycarbonyl-6- ( E-2 ′-methoxycarbonylvinyl)-cyclohepta-2,4-dien-1-yl-manganese ( 8 ). The crystal and molecular structure of 8 was determined by X-ray structure analysis. The molecular structures of the complexes 4 and 6 were established by IR and NMR spectroscopy. Formation mechanisms of 4 , 6 and 8 are discussed. Crystal data for 8 : monoclinic space group P 2 1 / c , a =802.6(3), b =1136.6(1), c =8872.3(3) pm, β=93.14(2)°, V =1.705 nm 3 , Z =4.

Enantioselective and Diastereoselective Tsuji-Trost Allylic Alkylation of Lactones: An Experimental and Computational Study

The Tsuji-Trost protocol has been successfully employed for the allylic alkylation of preformed lactone enolates. It has been demonstrated that this Pd-catalyzed reaction can be carried out in an enantio- and diastereoselective manner. The use of additives, such as LiCl, was found to be crucial for reaching high levels of product selectivity. For one particular pair of reactants, density functional theory was used to investigate the mechanism of the nucleophilic addition. Among the five pathways considered, the reaction between an (allyl)Pd(BINAP) complex and a LiCl-lithium enolate adduct is predicted to be the most likely route for C-C bond formation. LiCl plays a key role as the connecting link between the noble metal and the enolate in the kinetically favored transition state. The computed diastereoselectivity ratio is in good agreement with the experimentally observed value.

A novel application of DDQ as electrophile in the Nenitzescu reaction

Reaction of 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) with secondary enaminones yields surprisingly 2-aza-spiro[4,5]decatrienes. The reaction occurs via cyclisation of the primary Michael-adduct with the nitrile group. Reaction of DDQ with tertiary and also certain secondary enamines leads to 3-amino-benzo[b]furan derivatives. This is formed not by Michael-addition, but via geminate radical ion pair formation with subsequent generation of an oxygen-carbon bond to yield benzofurans. The new products are investigated with regards to inhibition of purified human proteinkinase CK2 and their general cytostatic activity. It turned out, that the most active compound is the 3-amino-5-hydroxy-benzofuran derivative 11s with an IC(50) value of 0,2μM for CK2.