Conversion of 1-alkenes into 1,4-diols through an auxiliary-mediated formal homoallylic C-H oxidation.

The ubiquitous nature of C-H bonds in organic molecules makes them attractive as a target for rapid complexity generation, but brings with it the problem of achieving selective reactions. In developing new methodologies for C-H functionalization, alkenes are an attractive starting material because of their abundance and low cost. Here we describe the conversion of 1-alkenes into 1,4-diols. The method involves the installation of a new Si,N-type chelating auxiliary group on the alkene followed by iridium-catalysed C-H silylation of an unactivated δ-C(sp(3))-H bond to produce a silolane intermediate. Oxidation of the C-Si bonds affords a 1,4-diol. The method is demonstrated to have broad scope and good functional group compatibility by application to the selective 1,4-oxygenation of several natural products and derivatives.

Synthesis of catechols from phenols via Pd-catalyzed silanol-directed C-H oxygenation.

A silanol-directed, Pd-catalyzed C-H oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product.

Experimental and theoretical characterization of the aromatization, epimerization, and fragmentation reactions of bi-2H-azirin-2-yls prepared from 1,4-diazidobuta-1,3-dienes.

1,4-Diazidobuta-1,3-dienes (Z,Z)-10, 17, and 21 were photolyzed and thermolyzed to yield the pyridazines 13, 20, and 23, respectively. To explain these aromatic final products, the generation of highly strained bi-2H-azirin-2-yls 12, 19, and 22 and their valence isomerization were postulated. In the case of meso- and rac-22, nearly quantitative formation from diazide 21, isolation as stable solids, and complete characterization were possible. On the thermolysis of 22, aromatization to 23 was only a side reaction, whereas equilibration of meso- and rac-22 and fragmentation, which led to alkyne 24 and acetonitrile, dominated. Prolonged irradiation of 22 gave mainly the pyrimidine 25. The change of the configuration at C-2 of the 2H-azirine unit was observed not only in the case of bi-2H-azirin-2-yls 22 but also for simple spirocyclic 2H-azirines 29 at a relatively low temperature (75 °C). The fragmentation of rac-22 to give alkyne 24 and two molecules of acetonitrile was also studied by high-level quantum chemical calculations. For a related model system 30 (methyl instead of phenyl groups), two transition states TS-30-31 of comparable energy with multiconfigurational electronic states could be localized on the energy hypersurface for this one-step conversion. The symmetrical transition state complies with the definition of a coarctate mechanism.

3-(Hetero)aryl-4-indolylamino-α-tetralones by diastereoselective internal redox cyclization: an "azaenamine" conjugate addition.

(E)-3-(hetero)aryl-1-(2-((E)-(indolin-1-ylimino)methyl)phenyl)prop-2-en-1-ones 1 undergo 6-exo-trig cyclization reactions upon treatment with BF(3)·Me(2)S in dichloromethane at low temperature to give the tetralones 10 in good yield. This cyclization process can be considered to be an intramolecular Michael-type addition which is accompanied by an internal redox reaction as the indoline fragment is oxidized to indole with simultaneous hydrogen shift to nitrogen atom N1 and the α-carbon atom of the Michael system. The reactions at the iminic centers take place via umpolung of the classical carbonyl reactivity. The reaction is diastereoselective and affords exclusively 3,4-disubstituted α-tetralones 10 as trans-diastereomers. According to quantum chemical calculations the reactions take place under kinetic control with the trans-diastereomer being the kinetically favored product as it has the lower activation barrier compared to the cis-diastereomer.

Synthesis of a GaN cage compound with a hydrazinetetraide fragment, [N-N]4-, stabilised by six gallium atoms.

Thermolysis of the bicyclic gallium hydrazide [(GaMe(2))(4)(NH-NMe)(NH-NHMe)(2)] (1) yielded the unique cage compound [(GaMe)(4)(GaMe(2))(4)(N(2))(NH-NMe)(4)] (2). Compound 2 contains a remarkable hydrazinetetraide moiety, [N-N](4-), as the central structural motif which is stabilised by coordination to six gallium atoms.

P-C dichotomy: divergent iron(-I)-mediated alkyne and phosphaalkyne cycloligomerisations.

In contrast to the recently reported cyclodimerisations of phosphaalkynes, alkynes preferably trimerise at the same low-valent iron(-I) centre.

Acid-mediated electrocyclic domino transformations of 5,5-disubstituted 1-amino-1-azapenta-1,4-dien-3-ones into dihydrospiroindenepyrazole and dihydroindenodiazepine derivatives.

Trifluoromethyl-substituted 1-amino-1-azapenta-1,4-dien-3-ones 4, which are accessible in good yield from pyruvates 1 in a three-step procedure, undergo a cascade reaction involving inter alia two electrocyclizations upon treatment with a large excess of trifluoromethanesulfonic acid to give novel dihydrospiroindenepyrazole 5a-o and dihydroindenodiazepine 6a-j. We interpret this sequence of reactions on the basis of quantum chemical calculations as a dicationic cyclization of a pentadien-1-one ("superelectrophilic solvation"), where one of the double bonds is part of an aromatic ring and a subsequent rearrangement to form an (monocationic) iminium ion, which either cyclizes to give five-membered spiro ring systems (compounds 5) or tricyclic dihydroindenodiazepine derivatives 6. Huckel- and Mobius-type transition states of the electrocyclization reactions are discussed considering the results of NICS calculations. One 1-amino-1-penta-1,4-dien-3-one 4 and several dihydrospiroindenepyrazoles 5 and dihydroindenodiazepines 6 could be characterized by X-ray diffraction.

The unique decomposition behavior of the dimeric dialkylaluminum hydrazide [(Me3C)2Al-N(H)-N(H)-Me]2-butane versus ammonia elimination.

The hydrazine adducts (Me3C)3E<--NH2-N(H)-Me [E = Al (1), Ga (2)] afforded the corresponding dimeric hydrazides [(Me3C)2E-N(H)-N(H)-Me]2 (3 and 4) upon heating to 95 and 300 degrees C, respectively, by the release of isobutane. The molecular structure of 3 in the solid state comprises a five-membered Al2N3 heterocycle (3b), while 4 possesses a four-membered Ga2N2 ring with two exocyclic hydrazine groups (4a). Quantum-chemical calculations revealed only small energetic differences between both isomers. The structures determined in the solid state correspond to the thermodynamically favored ones. In solution, equilibrium mixtures between both forms were detected. Further thermolysis of the aluminum compound 3 gave different products depending on the reaction conditions. Below its melting point, isobutane was released. A cage compound (5) was formed, which has four Al-CMe3 groups and four hydrazindiido ligands [N(H)-N(Me)]2- with all N-N bonds enclosed in the cage. Fast heating of 3 above the melting point (149 degrees C) yielded a singular product (6) by a remarkable rearrangement process and formal release of ammonia. The hydrazonido ligand [N(Me)-N(=CH2)]- resulted, which has a reformed N-N bond and an N=C double bond and is in a bridging position between two aluminum atoms. An amido group (NH2) completes the five-membered Al2N3 heterocycle of 6.