1,6‐Dinitroperylene Bisimide Dyes: Synthesis,Characterization and Photophysical Properties

1,6‐ and 1,7‐regioisomers of dinitro‐substituted perylene bisimides ( 1a — 1b and 2a — 2b ) were synthesized under mild condition in high yields. The 1,6‐ and 1,7‐regioisomers were successfully isolated from the regioisomeric mixture using conventional methods of separation and subsequently characterized by 500 MHz ¹H NMR spectroscopy. This is the first time when 1,6‐dinitroperylene bisimides ( 1a — 1b ) are obtained in pure form. Furthermore, the photophysical and electrochemical properties of 1 and 2 were found to be almost the same. The nitro functionalities provide stability of n‐type charge carriers by lowering the LUMO to resist ambient oxidation, which may offer potential applications in air‐stable n‐type organic semiconductors.     

1,6‐ and 1,7‐Regioisomers of Dicyano‐Substituted Perylene Bisimides: Synthesis,Optical and Electrochemical Properties

In this study, 1,6‐ ad 1,7‐regioisomers of dicyano‐substituted perylene bisimides (1,6‐ C and 1,7‐ C ) were synthesized and successfully isolated from their regioisomeric mixture using conventional methods of separation, and subsequently characterized by 400 MHz ¹H NMR spectroscopy. This is the first time that the 1,6‐dicyanoperylene bisimide 1,6‐ C has been obtained in pure form. Moreover, the optical and electrochemical properties of 1,6‐ C and 1,7‐ C were found to be virtually the same. Time‐dependent density functional theory calculations performed on both dyes are reported in order to rationalize their electronic structures and optical properties.     

1,7-Dinitroperylene bisimides: facile synthesis and characterization as n-type organic semiconductors

1,7-Dinitroperylene bisimides (1a-1b) and 1-nitroperylene bisimides (2a-2b) were synthesized under mild condition in high yields, and were characterized by FT-IR, ¹H NMR, UV-vis, HRMS spectra, cyclic voltammetry, and thermogravimetric analyses. These compounds are stable up to 260 °C according to thermogravimetric analyses. They undergo two quasi-reversible one-electron reductions in THF at modest potentials. The nitro functionalities provide stability of n-type charge carriers by lowering the LUMO to resist ambient oxidation.     

1,6-Disubstituted perylene bisimides: concise synthesis and characterization as near-infrared fluorescent dyes

Detailed studies on bromination and subsequent imidization of perylene bisanhydride were reported. 1,6,7,12-Tetrabromoperylene bisimide was obtained in an optimized high yield. In addition, 1,6-disubstituted regioisomer was separated for the first time in isomerically pure form, and the structure was confirmed by ¹H NMR, MS, element analysis, and photophysical measurements. By using a mixture of regioisomers 1,6- and 1,7-dibromo-perylene bisimide, 1,6-dipiperidinylperylene bisimides (1,6-Piper-Pery) were synthesized, purified, and their fluorescence were measured with a peak at 760 nm. These compounds can be used as stable near-infrared absorbing and fluorescent dyes.     

Tertiary amine effect: synthesis of some novel spirosubstituted pyrido[2,3-d]pyrimidines

5-Formyl-6-tertiaryamino uracils 3 prepared from 6-chloro-5-formyl uracil derivative 1 react with barbituric acids 4 in the presence of base catalyst to afford a novel class of spirosubstituted pyrido[2,3-d]pyrimidines 5 via 1,6-electro-cyclisation in excellent yields.     

An entry to 1,6-dioxaspiro[4.6]undecanes and 1,7-dioxaspiro[5.6]dodecanes

Ketones 11a-c obtained by iterative alkylation of acetone N,N-dimethylhydrazone with iodides 6 and 8a,b or epoxide 9 followed by SiO₂/H₂O-induced cleavage of the hydrazone were quantitatively transformed into 1,6-dioxaspiro[4.6]undecanes 12a,c and 1,7-dioxaspiro[5.6]dodecanes 12b using Yb(OTf)₃ in CH₃CN.     

Substituent-induced regioselective synthesis of 1,2-teraryls and pyrano[3,4-c]pyran-4,5-diones from 2H-pyran-2-ones

Substituent-controlled regioselective synthesis of highly functionalized 1,2-teraryls 3a-k has been achieved through ring transformation of 6-aryl-4-(pyrrolidin-1-yl/piperidin-1-yl)-2H-pyran-2-one-3-carbonitriles 1a-g by aryl acetones 2a-c in the presence of powdered KOH in DMF in very good yield. Under similar reaction conditions, 6-aryl-4-methylsulfanyl-2H-pyran-2-ones 5a-f afforded 1,7-diaryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-diones 6a-j as major products and 3,4-diaryl-2-methyl-6-methylsulfanylbenzonitriles as minor constituents 7a-j.     

Regioselective cyclization of unsymmetrical dicyanoanilines to novel 2,3-bifunctionalised indole regioisomers and their use in the synthesis of 4,5-dihydro[1,3]oxazino[5,4-b]indole-6-carbonitriles

Synthesis of novel-2,3-bifunctionalised indole regioisomers (2/3 and 6/7) from unsymmetrical dicyanoanilines 1 by regioselective cyclization in two independent ways. Regioisomers 6 are further utilized in synthesis of novel 4,5-dihydro[1,3]oxazino[5,4-b] indole-6-carbonitriles 9.     

Anti-Pseudomonas aeruginosa xanthones from the resin and green fruits of Cratoxylum cochinchinense

Cochinchinones I-L (1-3 and 13) along with 11 known xanthones (4-12, 14, and 15) were isolated from the resin and green fruits of Cratoxylum cochinchinense. In addition, four new acetylated compounds (16-19) were derivatized from 7-geranyloxy-1,3-dihydroxyxanthone (14) and 3-geranyloxy-1,7-dihydroxyxanthone (15). All compounds were characterized on the basis of spectroscopic analyses. The structures of cochinchinone I (1), a monoacetate (18) and a dibrosylate (20), were also confirmed by X-ray diffraction analysis. The antibacterial and antifungal activities of selected compounds were evaluated as well.     

The first reductive cyclization by lithium aluminum hydride: stereospecific reductive cyclization of 1-(methoxycarbonylmethyl)imidazolidin-4-ones

The first LiAlH₄-driven reductive cyclization of the bifunctional 1-(methoxycarbonylmethyl)imidazolidin-4-ones, (−)-1a-c or(+)-1a-c, stereospecifically generated the corresponding 1,6-diaza-4-oxa-bicyclo[3.2.1]octanes, (−)-3a-c or(+)-3a-c, with a novel bicyclic system.     

Furanyl spiroketals: thermodynamic control of remote asymmetry

(E,E)-2-Alkyl-8-furanyl-1,7-dioxa-spiro[5.5]undecanes (1a-i) have been prepared in good yield and with very high diastereoselectivity from lactones (2a-e) and alkynes (3a,b) using lithium acetylide coupling, hydrogenation, desilylation and acid catalysed cyclisation/equilibration.     

Synthesis of nicotinonitrile derivatives as a new class of NLO materials

4,6-Diaryl-2-(pyrrolidin-1-yl)-nicotinonitriles 2a-k and 3-amino-2,4-dicyano-5-aryl-biphenyls 3a-c were synthesized from 1,3-diaryl-prop-2-en-1-ones 1a-k and malononitrile by a convenient one-pot method. Likewise, the reaction of aromatic aldehydes with malononitrile afforded 6-amino-4-aryl-2-(pyrrolidin-1-yl)-pyridine-3,5-dicarbonitriles 6a-f. The reaction of mesityl oxide with malononitrile gave 5-amino-7-(pyrrolidin-1-yl)-2,4,4-trimethyl-1,4-dihydro-1,6-naphthyridine-8-carbonitrile 8. The NLO studies of the pyridinedinitrile derivatives 6a, b, f showed a high value while that of nicotinonitrile 2b was weak.     

Dioxadispiroketal Compounds and a Potential Acyclic Precursor from Amomum aculeatum

Four new compounds having an unusual 1,7-dioxadispiro[5.1.5.2]-12-ene-11-one tricyclic ring system (1-4), their potential precursor, 5R-hydroxy-1-(4-hydroxyphenyl)-eicosan-3-one (5), and two known compounds, aculeatins A (6) and B (7), have been isolated from Amomum aculeatum. All compounds were characterized by spectroscopic methods and the configurations were established by 2D NOE correlations. Compounds 1-4, 6, and 7 showed cytotoxic activity against several human cancer cell lines.     

Naphthyridines. Part 3: First example of the polyfunctionally substituted 1,2,4-triazolo[1,5-g][1,6]naphthyridines ring system

Treatment of 1,2,4-triazoles (1) with diethylmalonate in bromobenzene gave 1,2,4-triazolo-[1,5-a]pyridines 2. Chlorination of 2 using POCl₃/DMF (Vilsmeier reagent) led to the isolation of 7-chloro-6-formyl-1,2,4-triazolo[1,5-a]pyridine derivative 4, which reacted with the stabilized ylid 5 to afford 6-ethoxycarbonylvinyl-1,2,4-triazolo[1,5-a]-pyridines 6. Azidation of 6 yielded the corresponding azido compound 7, (Scheme 2). Reduction of 7 with Na₂S₂O₄ gave the corresponding 7-amino compound 8, which cyclized in boiling DMF to give the novel 1,2,4-triazolo[1,5-g][1,6]naphthyridines 9. On the other hand, reacting 7 with one equivalent of PPh₃ (aza-Wittig reaction) in CH₂Cl₂ gave 7-imino-phosphorane derivative 10, and subsequent cyclization in boiling DMF afforded the new 1,2,4-triazolo[1,5-g][1,6]naphthyridine derivative 11 (Scheme 3). However, treatment of 10 with phenyl isothiocyanate in 1,2-dichlorobenzene at reflux temperature gave the new 1,2,4-triazolo[1,5-g][1,6]naphthyridine derivative 14 (Scheme 4). Refluxing 6 with excess of a primary amines 15a,b in absolute. EtOH yielded the corresponding 7-alkyl-amino-1,2,4-triazolo[1,5-a]pyridines 16a,b. These obtained amines 16a,b underwent intramolecular heterocyclization in boiling DMF to give the novel 9-alkyl-1,2,4-triazolo[1,5-g][1,6]-naphthyridines 17a,b, in excellent yields (Scheme 5).     

De-novo approach for a unique spiro skeleton-1,7-dioxa-2,6-dioxospiro[4.4]nonanes

2-Oxoglutaric acid (1) underwent facile indium mediated allylation with allyl bromide (2), and ethyl 4-bromocrotonate (3), cinnamyl bromide (4) and subsequent in situ dehydration to provide respective 5-oxotetrahydrofuran-2-carboxylic acids 5-7 (90-95%). The reaction of 1 with 3 and 4 proceeded with high regio and stereo selectivity to provide only γ-addition products with syn stereochemistry as ascertained from their cyclic products. Compounds 5-7 underwent diastereoselective iodocyclization to provide respective 1,7-dioxa-2,6-dioxospiro[4.4]nonanes 8-13. The relative stereochemistries have been ascertained by single crystal X-ray structures, NOE experiments and coupling constants in ¹H NMR spectra.     

Donor-acceptor-donor triads incorporating tetrathiafulvalene and perylene diimide units: synthesis, electrochemical and spectroscopic studies

Three donor-acceptor-donor triads 1-3 consisting of tetrathiafulvalene units attached to perylene diimides by flexible and rigid spacers were synthesized and characterized. UV/vis spectroscopic and cyclic voltammetric results indicate that they all show negligible intramolecular charge transfer interaction in their ground states. As compared to the reference compound 21, triads 1-3 display reduced fluorescence and their fluorescence lifetimes are shortened, which is probably owing to the photoinduced electron transfer interactions between the PI units and TTF units. The different photophysical behaviors between 1 and 2 (and 3) might be due to their difference in the spatial separation of TTF and PI units. It is preliminarily found that the steric hindrance of the groups attached to TTF units can affect their photostability.     

Hydroacylation of 2-butyne from the alcohol or aldehyde oxidation level via ruthenium catalyzed C-C bond forming transfer hydrogenation

Under the conditions of ruthenium catalyzed transfer hydrogenation, 2-butyne couples to alcohols 1a-1j to deliver α,β-unsaturated ketones 3a-3j in good to excellent isolated yields with complete E-stereoselectivity. Under identical conditions, aldehydes 2a-2j couple to 2-butyne to provide an identical set of α,β-unsaturated ketones 3a-3j in good to excellent isolated yields with complete E-stereoselectivity. Nonsymmetric alkyne 4a couples to alcohol 1d or aldehyde 2d in good yield to deliver enone 3k as a 5:1 mixture of regioisomers. Thus, intermolecular alkyne hydroacylation is achieved from the alcohol or aldehyde oxidation level. In earlier studies employing the same ruthenium catalyst under slightly different conditions, alkynes were coupled to carbonyl partners from the alcohol or aldehyde oxidation level to furnish allylic alcohols. Therefore, under the conditions of C-C bond forming transfer hydrogenation, all oxidation levels of substrate (alcohol or aldehyde) and product (allylic alcohol or α,β-unsaturated ketone) are accessible.     

Velutabularins A-J, phragmalin-type limonoids with novel cyclic moiety from Chukrasia tabularis var. velutina

Velutabularins A-J, ten novel phragmalin-type limonoids, were isolated from the stem bark of Chukrasia tabularis var. velutina. In structures of 1-6, the tetrahydrofuran ring from dehydration of OH-15 and OH-17, ring C and 13/14/18-cyclopropanyl moiety formed an unprecedented 8-oxatricyclo[4,3,1^1,6]decane. Compounds 7-10 are derivates of 1-6 opening the tetrahydrofuran ring. All of these compounds possess a novel C-16/C-30 δ-lactone ring, which were reported in phragmalins rarely. The structures of these novel compounds were elucidated based on extensive 1D and 2D spectroscopic analysis. The absolute configuration of 5 and 9 were determined by the calculated electronic circular dichroism (ECD) method. The anti-inflammatory activities of major compounds (2, 4, 5, 9) were evaluated for inhibitory activity against lipopolysaccharide (LPS) induced nitric oxide (NO) production in macrophage (RAW264.7) cell line.     

A simple approach for the regioselective synthesis of imidazo[1,2-a]pyrimidiones and pyrimido[1,2-a]pyrimidinones

Several imidazo and pyrimido[1,2-a]pyrimidinones of type 1 and 2 were synthesized through intramolecular cyclization of pyrimidines 9 or pyrimidinones 10 bearing a variety of β and γ-aminoalcohols at the 2-position. Ring closure of the pyrimidinones of type 10 under Mitsunobu conditions lead to mixtures of both bicyclic regioisomers 1 and 2. Treatment of pyrimidines of type 9 with H₂SO₄ provided an efficient and operationally simple one-pot hydrolysis-cyclization procedure for obtaining imidazo and pyrimido[1,2-a]pyrimidinones 1 in good yields as the sole regioisomeric bicyclic product.     

Synthesis of thiacrown and azacrown ethers based on a spiroacetal framework

A novel class of thiacrown and azacrown ethers incorporating the 1,7-dioxaspiro[5.5]undecane spiroacetal ring system was prepared by reaction of ditosylate 5 with the appropriate dithiols 9a-c or protected diamine 12a. Spiroacetal ditosylate 5 in turn, was prepared from diol 3 via ozonolysis of bisallyl ether 7 followed by tosylation of the derived diol 8.