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.     

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.     

The first benzodiazepine o-quinodimethane: generation and Diels-Alder reactions

7,8-Bis(dibromomethyl)-3-bromo-2,4-diphenyl-3H-benzodiazepine 1 was used as a precursor for the benzodiazepine o-quinodimethane 2, which was trapped by in situ reactions with dienophiles.     

Mild generation of o-quinodimethanes via fluoride induced 1,4-elimination of α-(o-trimethylsilylmethyl)benzylesters: stereoselective synthesis of 19-nor steroids and RU486 precursors

19-Nor steroids and RU486 tricyclic synthetic intermediates were stereoselectively prepared by an intramolecular Diels-Alder reaction involving an o-quinodimethane possessing a pro-17 unique chiral stereocenter, substituted by a protected hydroxyl group. The o-quinodimethane was generated in mild conditions by fluoride induced 1,4-elimination of α-(o-trimethylsilylmethyl)benzylesters and the present methodology allows a flexible access to α,α′-disubstituted o-quinodimethanes, as shown by the 11β-substituted steroid approach. The IMDA diastereoselections reported herein were highly dependent on the nature of the hydroxyl protective group and the diastereoselectivities superior to those observed with the thermolysis of the corresponding benzocyclobutenes.     

Chromone-3-carboxaldehydes in Diels-Alder reactions with indole-o-quinodimethane. Synthesis of tetrahydrochromeno[2,3-b]carbazoles

An efficient route to a new class of indole derivatives, tetrahydrochromeno[2,3-b]carbazoles, has been developed. The cycloaddition reactions of chromone-3-carboxaldehydes with indole-o-quinodimethane gave a diastereomeric mixture of Diels-Alder cycloadducts in good yields after in situ deformylation.     

The first application of an imidazole o-quinodimethane in Diels-Alder reactions leading to the synthesis of benzimidazoles

An efficient procedure for the generation of the imidazole-4,5-quinodimethane intermediate 4 from 2-bromo-4,5-bis(bromomethyl)imidazole derivative 3 in boiling toluene in the presence of 18-crown-6 is described. o-Quinodimethane 4 was captured for the first time by several symmetrically and unsymmetrically substituted dienophiles to afford the corresponding Diels-Alder benzimidazole adducts.     

Reaction of meso-tetraarylporphyrins with pyrazine ortho-quinodimethanes

Novel π-extended porphyrins were obtained from the Diels-Alder reaction of meso-tetraarylporphyrins with a pyrazine o-quinodimethane derivative.     

Thermodynamically Stable o-Quinodimethane: Synthesis,Structure, and Reactivity

Thermal isomerization of cyclobutaphenanthrene to o-quinodimethane was investigated. Sterically congested substituents or electron-donating substituents on the four-membered ring promoted the ring-opening, affording o-quinodimethane in a relatively stable form. Isolation of the newly prepared o-quinodimethane allowed its structural elucidation and investigation of its potential reactivities. Dual [4+2] cycloaddition of an aryne and o-quinodimethane afforded tetrabenzopentacene, demonstrating the synthetic application of the isolated compound.     

Synthesis of 1H-Cyclopropa[b]naphthalenes via Trapping of o-Benzoquinodimethanes

1H-Cyclopropa[b]naphthalene ( 10a ) and 3-methyl or dimethyl derivatives have been synthesized by interception of appropriately substituted o-quinodimethanes 3 with 1-bromo-2-chlorocyclopropene 5 , and subsequent dehydrohalogenation of the adducts. The o-quinodimethane derivatives 3 in turn were obtained from the diynes 7 via base-induced isomerization to bisallenes 8 and thermal electrocyclic ring closure.     

A facile method for the synthesis of steroidal and nonsteroidal 5-methyl pyrazolo[1,5-a]pyrimidines

The steroidal and nonsteroidal 5-methyl pyrazolo[1,5-a]pyrimidines were synthesized by the reaction of steroidal/nonsteroidal α,β-unsaturated ketones and 3-amino-1H-pyrazoles/5-amino-1H-pyrazoles in the presence of KO^tBu in ethanol under reflux condition.     

Novel porphyrin-quinazoline conjugates via the Diels-Alder reaction

Novel derivatives of meso-tetraphenylporphyrin with appended quinazoline moieties were synthesized, via the Diels-Alder reaction, between a 4-(porphyrinyl)pyrimidine ortho-quinodimethane and 1,4-benzoquinone, 1,4-naphthoquinone and N-(p-nitrophenyl)maleimide. The structure of one bis adduct was established by X-ray crystallography and mass spectrometry. We have unequivocally confirmed that the 2:1 adducts obtained from the reaction of pyrimidine-fused 3-sulfolenes with N-arylmaleimides have an open-chain structure and not a cyclooctapyrimidine structure, as previously published.     

Simple total synthesis of 18-hydroxyestrone

A simple total synthesis of 18-hydroxyestrone ($\text{7}$) was carried out by the cycloaddition of o-quinodimethane intermediate. 2-Methoxycarbonyl-3-vinyl-cyclopentanone ($\text{1}$) was used as the D ring component.     

Regioselective synthesis of triiodo-o-carboranes and tetraiodo-o-carborane

3,6-Diiodo-o-carborane 3, 3,6,9-triiodo-o-carborane 5, 3,9,12-triiodo-o-carborane 6 and 3,6,9,12-tetraiodo-o-carborane 7, which are suitable building blocks for supramolecular assemblies and carboracycles, were regioselectively synthesized by means of electrophilic iodination and introduction of iodine atoms via reconstruction of the o-carborane cage.     

Reaction of 5,6-dimethylene-7-oxabicyclo[2.2.1]hept-2-ene with iron carbonyls

The photoreaction of 5,6-dimethylene-7-oxabicyclo[2.2.1]hept-2-ene with Fe(CO)₅ yields initially the dihapto-tetracarbonyliron complex, which reacts further to give a dihapto-tetracarbonyl-tetrahapto-tricarbonyl complex. Deoxygenation of the ligand is observed in the presence of Fe₂ (CO)₉ in benzene, giving o-quinodimethane complexes.     

Photoacid generators (PAGs) based on N-acyl-N-phenylhydroxylamines for carboxylic and sulfonic acids

Simple and efficient photoacid generators (PAGs) for carboxylic and sulfonic acids based on N-acyl-N-phenylhydroxylamines have been demonstrated. Irradiation of o-carboxylates and thermally rearranged o-arenesulfonates of N-acyl-N-phenylhydroxylamines using UV light (≥254 nm) in aqueous methanolic solution resulted in efficient generation of carboxylic and sulfonic acids, respectively. The carboxylic acid generation ability of N-acyl-N-phenylhydroxylamines was found to be dependent on their N-acyl substituents. Further, polymer bearing o-arenesulfonates of N-acyl-N-phenylhydroxylamine was synthesized and demonstrated as PAG for sulfonic acids.     

Bioactive pregnane-type steroids from the soft coral Scleronephthya gracillimum

Nine new steroids, sclerosteroids A-I (1, 5, 6, 8-13), along with 18 known metabolites (2-4, 7, 14-27), were isolated from the soft coral Scleronephthya gracillimum. These structures were elucidated on the basis of detailed spectroscopic analysis. The absolute configurations of sugar moieties in steroidal glycosides 10-13 were determined by HPLC analysis of the o-tolylthiocarbamate derivatives of the liberated sugars from hydrolysis of these steroidal giycosides. Cytotoxic and anti-inflammatory activities of these compounds were measured in vitro.     

NMR study of 1-aryl-1,2-dicarba-closo-dodecaboranes: intramolecular C-H?O hydrogen bonding in solution

Dicarba-closo-dodecaborane(12) (carborane) has recently received much attention as a building block for supramolecular assemblies and bioactive compounds. Among carborane isomers, 1,2-dicarba-closo-dodecaborane(12) (o-carborane) has unique chemical properties, including the ability of the o-carborane C-H hydrogens to form hydrogen bonds. To evaluate intramolecular hydrogen bond formation between the o-carborane C-H hydrogen and various hydrogen bond acceptors in solution, we have designed and synthesized 1-aryl-o-carboranes 2. Intramolecular hydrogen bonding ability was evaluated by means of ¹H NMR measurement of the o-carborane C-H hydrogen signal of 2. The 1-(2-methoxyphenyl)-o-carborane derivative 2m appeared to form an intramolecular hydrogen bond between o-carborane C-H hydrogen and the oxygen atom acting as a hydrogen bonding acceptor. In this study, we present evidence for hydrogen bond formation in solution between the o-carborane C-H and hydrogen bond acceptors positioned with appropriate geometry.     

First SNAr reaction using TDAE-initiated carbanions in quinazoline series

We report herein the first example of a S_NAr reaction using TDAE-initiated carbanions in quinazoline series. The o-nitrobenzyl carbanion, formed by the action of TDAE on o-nitrobenzyl chloride, reacts with 4-chloro-2-trihalomethylquinazolines 4 and 5 via a S_NAr mechanism. This enabled a new series of 4-benzyl-2-trihaloquinazoline derivatives to be synthesized in good yields under mild reaction conditions offering promising prospects for pharmacomodulation.     

Proline-catalyzed asymmetric Diels–Alder reactions of an o-quinodimethane

Catalytic asymmetric Diels–Alder reaction of α-amino-o-quinodimethane with α,β-unsaturated aldehydes was achieved with high diastereo- and enantioselectivities in the presence of l-proline, which acts as a promoter to generate the quinodimethane from the corresponding precursor as well as a chiral catalyst for the enantioselective Diels–Alder reaction.     

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’.