Novel synthesis of o-naphthothiophenequinone derivatives via regioselective Diels-Alder reaction

A novel procedure to construct o-naphthothiophenequinones has been achieved from readily available o-benzothiophenquinones and N-dienes via Diels-Alder reaction-aromatization sequence as key steps. The absolute regioselectivity was established via Diels-Alder reaction of o-benzothiophenquinones with rich electron N-dienes.     

Interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines—a pathway to new sterically hindered N,N-disubstituted o-aminophenols

The interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines has been studied. The synthetic procedure was developed in order to synthesize a series of new N,N-disubstituted o-aminophenols. The interaction of 3,5-di-tert-butyl-o-benzoquinone with dimethylamine leads to 2-(N,N-dimethylamino)-4,6-di-tert-butyl-phenol, which is oxidized in the reaction medium by the parent 3,5-di-tert-butyl-o-benzoquinone forming spirocompound 4,5′,6,7′-tetra-tert-butyl-3′-methyl-3′H-spiro[1,3-benzodioxol-2,2′-[1,3]benzoxazole].     

Dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes with lanthanum metal

It was found that lanthanum metal caused the dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes to generate the corresponding benzynes and o-quinodimethanes. When o-dihalogen substituted arenes were allowed to react with lanthanum metal in the presence of dienes, the Diels-Alder products between benzyne and dienes were formed in moderate to good yields. Similarly, the Diels-Alder adducts of o-quinodimethane with dienophiles were obtained, in the reaction of α,α′-dibromo-o-xylenes with lanthanum metal in the presence of dienophiles.     

Photolytic decarbonylation of o-benzoquinones

It was established that photodecarbonylation of o-benzoquinones occurs by irradiation not only by UV-light, but visible light (λ>520 nm) too. Study of the series of 4,5-di-substituted 3,6-di-tert-butyl-o-benzoquinones detected that the only product of photoreaction is the corresponding 3,4-di-substituted 2,5-di-tert-butyl-cyclopentadienone, which is formed in a yield close to quantitative. NMR monitoring of reaction of photodecarbonylation of o-benzoquinones detected that this is a two-stage process. In the first stage the photoexcited molecule of quinone rearranges into bicyclo compound (bicyclo[1.3.0]hexa-3-en-2,6-dione) containing five- and three- membered cycles, which spontaneously decomposes during the following dark stage into cyclopentadienone and a molecule of CO.     

A new class of o-hydroxyaryl-substituted N-heterocyclic carbene ligands and their complexes with palladium

A facile synthesis of o-hydroxyaryl-substituted N-heterocyclic carbene ligands and their complexes with palladium is presented. This kind of salicylaldimine-like NHC ligands expands the class of available NHC ligands for organometallic catalysts.     

Synthesis of photolabile o-nitroveratryloxycarbonyl (NVOC) protected peptide nucleic acid monomers

The chemical synthesis of peptide nucleic acid (PNA) monomers was accomplished using various combinations of the o-nitroveratryloxycarbonyl (NVOC) group (N-aminoethylglycine backbone) and base labile acyl-type nucleobase protecting groups (anisoyl for adenine and cytosine; isobutyryl for guanine), thus offering a photolithographic solid-phase PNA synthetic strategy compatible with photolithographic oligonucleotide synthesis conditions and allowing the in situ synthesis of PNA microarrays in an essentially neutral medium, by avoiding the use of the commonly used deprotection reagents such as trifluoroacetic acid or piperidine. Convenient methods were also explored to prepare 1-(carboxymethyl)-4-N-(4-methoxybenzoyl)cytosine and 9-(carboxymethyl)-2-N-(isobutyryl)guanine with good yields.     

Synthesis of 3-substituted-4-hydroxyquinoline N-oxides from the Baylis-Hillman adducts of o-nitrobenzaldehydes

The reaction of the Baylis-Hillman adducts 1b-f derived from o-nitrobenzaldehydes in trifluoroacetic acid in the presence of triflic acid (0.2 equiv.) afforded 3-substituted-4-hydroxyquinoline N-oxides 2b-e and 2a in good to moderate yields. The reaction mechanism was evidenced by the experiment with 1f, the Baylis-Hillman adduct of 2-nitrobenzaldehyde N-tosylimine, as the one involving N-hydroxyisoxazoline as the key intermediate.     

Preparation and oxidative coupling of bis[o-(hydrosilyl)phenyl]cuprates and bis[o-(fluorosilyl)phenyl]cuprates

Bis[o-(hydrosilyl)phenyl]cuprates and bis[o-(fluorosilyl)phenyl]cuprates were prepared by reacting [o-(hydrosilyl)phenyl]lithiums and [o-(fluorosilyl)phenyl]lithiums, respectively, with copper salts, such as CuCN and Cu(OPiv)₂. The phenylcuprates underwent oxidative coupling to afford 2,2′-bis(hydrosilyl)biphenyls and 2,2′-bis(fluorosilyl)biphenyls.     

Enantioselective organocatalytic aryloxylation of aldehydes with o-quinones

An enantioselective organocatalytic inverse electron demand hetero Diels-Alder reaction of in situ generated enamines with o-quinone reagents is reported. The method, which is optimal in wet acetonitrile at ambient temperature, provides a new and direct asymmetric route to the aryl alkyl ether motif and an alternative metal-free strategy to S_N2 substitutions with phenolate nucleophiles.     

The synthesis and characterisation of novel o-substituted benzyldi-t-butylphosphine-boranes

The novel compounds o-(chloromethyl)benzyldi-t-butylphosphine-borane and o-(methoxymethyl)benzyldi-t-butylphosphine-borane have been synthesised in 54% and 51% yields, respectively, and have been fully characterised. An improved method for the synthesis of α-chloro-α′-methoxy-o-xylene is also reported.     

N-Heterocyclic carbene catalyzed intramolecular crossed aldehyde-ketone benzoin condensation in the chalcone of o-phthalaldehyde: a facile synthesis of naphthalenones

The intramolecular crossed aldehyde-ketone benzoin condensation in the chalcone of o-phthalaldehyde (OPA) catalyzed by N-heterocyclic carbene (NHCs) generated in situ from readily available imidazolium and thiazolium salts is described. In this reaction, bicyclic α-hydroxyl ketones (naphthalenone type tertiary alcohol) were selectively produced in good yields (75-94%) in shorter reaction times (20 min) through nucleophilic addition of acyl anion generated by umpolung in OPA-chalcone (regio controlled).     

Reactions of Ru(Cp) complexes with P(o-tolyl)3

Reaction of [Ru(Cp^∗)(CH₃CN)₃](PF₆) with P(o-tolyl)₃ affords [Ru(Cp^∗){(η⁶-o-tolyl)P(o-tolyl)₂}](PF₆) (4) in which the P-atom is not coordinated to the metal. The solid-state structure of 4 has been determined. A related reaction with P(p-tolyl)₃ reveals a small quantity [Ru(Cp^∗){(η⁶-p-tolyl)P(o-tolyl)₂}](PF₆), in solution, but mostly the expected bis-phosphine complex. Reaction of the Ru(IV) dication, [Ru(Cp^∗)(η³-PhCHCHCH₂)(DMF)₂](PF₆)₂, with P(o-tolyl)₃ gives a mixture of the phosphonium salt, C₆H₅CHCHCH₂P(o-tolyl)₃ (9) and the dication [Ru(Cp^∗) (η⁶-C₆H₅CHCHCH₂P(o-tolyl)₃)](PF₆)₂ (10). Salt 9 forms via attack of the P-atom on the allyl ligand. The latter product results from complexation of 9 via the phenyl group of the former allyl ligand. It would seem that the sterically demanding P(o-tolyl)₃ ligand is not readily compatible with the Ru(Cp^∗) fragment, in either the +2 or +4 oxidation state. Detailed NMR studies are reported.     

Asymmetric radical cyclization reactions of axially chiral N-allyl-o-iodoanilides to form enantioenriched N-acyl dihydroindoles

Radical cyclizations of enantiomerically enriched N-allyl-o-iodoanilides provide N-acyl-3-alkyl-2,3-dihydroindoles in good yields and with good to excellent levels of chirality transfer from the N-Ar axis to the new stereocenter. In competitive cyclizations of N-acryloyl-N-allyl-o-iodoanilides, the addition of an o-methyl group reverses the regioselectivity of the radical cyclization from the acryloyl group to the allyl group. Approximate rate constants for representative radical cyclizations have been measured to provide insight into the origin of these observations.     

Synthesis of polycyclic pyrazoles through formation of the first fused heterocyclic o-quinodimethane intermediate

1-Benzoyl-4,6-dibromo-3-methyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2) was used as a precursor for o-quinodimethane 3, which was trapped by in situ reactions with dienophiles to give bridged pyrazole derivatives.     

Infrared spectra of p-, m- and o-fluorobenzaldehyde in low temperature argon matrices

Three structural isomers of fluorobenzaldehyde (p-, m- and o-forms) have been investigated in detail with matrix-isolation infrared spectroscopy, in the 700-3000 cm⁻¹ region, combined with the UV photoexcitation and the density functional calculations. Two rotamers (syn and anti) were identified for m- and o-fluorobenzaldehyde upon the photoexcitation and most of the bands of each rotamer were assigned. It is shown that the formation of the intramolecular C-H?F hydrogen bond for the anti rotamer of o-FB results in the shortening of the aldehyde C-H bond length and that the C-F and/or CO bond lengths are shortened for the syn rotamer of o-FB presumably due to the repulsion between the aldehyde O and F atoms.     

Reactivity and regioselectivity in the synthesis of spiroindoles via indole o-quinodimethanes. An experimental and computational study

The 1,3-dipolar cycloaddition reactions of stable nitrile oxides with indole o-quinodimethanes have been examined. In all cases the ‘exo-anti’ addition products, dispiroisoxazolines, were isolated in moderate to good yields (25-47%). In addition, from the reaction of one of the indole quinodimethanes with mesitonitrile oxide the ‘exo-syn’ addition product was isolated in 7% yield along with the remarkable indole quinodimethane dimerization and cycloaddition product, which was isolated in 13% yield. An analogous dimerization and cycloaddition product was isolated in 18% yield from the reaction of the N-acetyl-indole quinodimethane with mesitonitrile oxide. In the case of the reaction of the N-benzoylindole quinodimethane with the 2,6-dichlorobenzonitrile oxide an oxime was also isolated in 13% yield. The proposed reaction mechanism is supported by semiempirical (AM1) MO calculations via FMO interactions. The observed selectivity was explained by an investigation of the transition states carried out also for analogous dispiroisoxazolines.     

Comparative studies of chemically synthesized polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid

Polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid (p-TSA) were synthesized by in situ chemical polymerization method using ammonium per sulphate as an oxidizing agent. This is a novel polymerization process for the direct synthesis of emeraldine salt phase of the polymer. The polymers were characterized by using UV-Vis and FT-IR spectroscopy, SEM, elemental analyzer, TGA/DSC and conductivity measurements. Thermal analysis shows that poly(o-toluidine) is less thermally stable compared to polyaniline. The less conductivity in poly(o-toluidine) is due to the cumulative steric as well as electronic effect of the bulky methyl substituent present on the benzene ring. High temperature conductivity measurements show ‘thermal activated behavior’.     

Construction of nitrogen-heterocyclic compounds through zirconium mediated intramolecular alkene-carbonyl coupling reaction of N-(o-alkenylaryl)carbamate derivatives

Intramolecular alkene-carbonyl coupling reaction of N-benzyl-N-(o-alkenylaryl)carbamate derivative derived from o-aminostyrene, o-(aminomethyl)styrene and o-aminoallylbenzene smoothly proceeded by treating with zirconocene-butene complex to give the corresponding lactam derivative.     

Reversal of the regioselectivity in a cycloaddition of o-quinones by varying the position of alkoxy substituents

We have investigated the regioselective cycloaddition of o-quinones 1b-e with the protected sinapyl alcohol 2. It was found that the position of the alkoxy substituent on the o-quinone ring controlled the regioselectivity of the cycloaddition. In addition, our reported procedure for determining the location of the side chains on 1,4-benzodioxanes has been improved.     

Tandem addition-cyclization of o-ethynylphenyllithiums and isoselenocyanates: a convenient preparation of functionalized benzo[c]selenophenes

The o-bromoethynylbenzenes were lithiated with tert-BuLi in Et₂O followed by treatment with isoselenocyanate, and then EtOH was added as a proton source, producing the desired (Z)-3-methylidenebenzo[c]selenophenes as the sole 5-exo-dig mode cyclization products in one-pot with yields ranging from 54-87%. The iodocyclization of the o-ethynylphenyllithium with isoselenocyanate stereoselectively gave the (E)-1′-iodo-3-methylidenebenzo[c]selenophene, which was converted into the more functionalized benzo[c]selenophenes via the Suzuki- and Sonogashira-coupling reactions.