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A two-step synthetic protocol involving (i) a Wittig-type carbonyl olefination, and (ii) regioselective alkylation of the exocyclic double bond with LiAlH4 and an alkyl bromide, was developed as an alternative to the recently reported three-step synthetic approach toward asymmetrically substituted/functionalized 4H-cyclopenta[2,1-b:3,4-b′]dithiophenes. The two routes are rather complementary, with specific advantages depending on the desired substitution pattern, and are of particular appeal for the construction of semiconducting materials to be applied in organic photovoltaics.

In this Letter we report on the reaction of 4H-cyclopenta[2,1-b:3,4- b‚A≤]dithiophen-4-one with various trivalent organophosphorus derivatives, with an emphasis on the final products depending on the applied reagents. No reaction occurred upon treatment with either triphenyl- or tricyclohexylphosphine, whereas addition of triethyl phosphite or tri(n-butyl)phosphine resulted in pinacol rearrangement. Structure elucidation of the isolated 5H-spiro(benzo[1,2-b:6,5-b‚A≤]dithiophene-4,4‚A≤- cyclopenta[2,1-b:3,4-b‚A≤]dithiophen)-5-one was achieved by combined NMR experiments, theoretical chemical shift and geometry calculations, and single crystal X-ray analysis.

Two variations of a parallel solution-phase synthesis of N-substituted dimethyl 4-oxo-1,4-dihydropyridine-3,5-dicarboxylates 4 and methyl 3-oxo-3,5-dihydro-2H-pyrazolo[4,3-c]pyridine-7-carboxylates 9 from dimethyl acetone-1,3-dicarboxylate (1) were developed. The first synthetic method comprises preparation of the bis-enaminone reagents 2 and 8 and their cyclization with primary amines 3 via double substitution of both dimethylamino groups to give dihydropyridines (DHPs) 4 and 9, respectively. Another variation consists of preparation of the monoenaminone reagents 5 and 10, followed by substitution of the dimethylamino group with primary amines 3, and cyclization of the so formed intermediates 6 with N,N-dimethylformamide dimethylacetal (DMFDMA). In this manner, a library of 46 analytically pure compounds, 24 intermediates 6, 11, and 13, and 22 final dihydropyridines 4 and 9 was obtained employing just a simple filtration workup.

A simple and efficient synthesis of four new substituted pyrimidines, compounds 9a–d, from the title compound 3 is described. Conversion of 3 to methyl (E)-3-(dimethylamino)-2-(6-methoxy-2-phenylpyrimidin-4-yl)prop-2-enoate (4), followed by condensation with various dinucleophiles according to the ‘enaminone methodology’, afforded the target compounds 9 in medium-to-good yields.

Combinatorial solution-phase cycloadditions of (1Z,4R*,5R*)-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines 3 to beta-keto esters 4 afforded a library of 26 bicyclic pyrazolidinones 5 in 6-89% yields and in 14-100% de. All products were isolated in90% purity according to 1H NMR, and 25 of them were analytically pure. The structures of cycloadducts were confirmed by NMR and X-ray diffraction. Most of the products were isolated as mixtures of the major (1S*,2S*,3R*,5R*,6R*)-epimers 5 and the minor (1R*,2S*,3R*,5R*,6R*)-epimers 6. Epimerization of cycloadducts 5/6 at the anomeric position 1 in solution was confirmed by 1H NMR.

A simple and efficient synthesis of novel 2-heteroaryl-substituted 1H-indole-2-carboxylates and γ-carbolines, compounds 1–3, from methyl 2-(2-methoxy-2-oxoethyl)-1-methyl-1H-indole-3-carboxylate (4) by the enaminone methodology is presented.

The reaction of xenon difluoride with enamino lactone 3 furnished the new α-fluoro aldehyde 7, whereas reaction of 3 with anhydrous HF led to racemic dihydro-β-campholenolactone 6. Acid-catalysed rearrangement of α-ethylidenelactone 4 proceeded with retention of configuration to give β-campholenolactone 8. Nitrosation of the novel bicyclic enamino lactone 6 afforded the corresponding oxime 9, while acid-catalysed treatment with primary amines, 2-methyl-1H-indole, potassium cyanide and hydrazine hydrochloride, furnished the dimethylamine substitution products 11–13 and the ‘ring switched’ product 14. The structures were determined by 2D NMR techniques, NOESY spectroscopy and X-ray diffraction.

Protected N(11')-substituted (S)-3-(4-methoxycarbonyl-1H-pyrazol-5-yl)alanines 7a-h were prepared in 34-94% yields by acid-catalysed cyclocondensations of chiral enaminone 5, available from L-aspartic acid, with hydrazines 6a-h hydrochlorides. Deprotection of 7a,b,e by catalytic hydrogenation afforded the corresponding free pyrazoylalanines 8a,b,e. On the other hand, 1-benzyl 6-methyl (S)-2-benzyloxycarbonylamino-4-oxohexanedioate (4), precursor of the enaminone 5, reacted with hydrazines 6 in two different ways. In the reactions of 4 with (hetero)arylhydrazines 6b,e,i, the five-membered ring was formed and the corresponding 3-pyrazolylalanine esters 10b,i and 10'e were obtained, whilst treatment of 4 with hydrazine hydrate (6a) and methylhydrazine (6h) led to the formation of the six-membered ring furnishing tetrahydropyridazinones lla,h.

Stereoselective additions to the exocyclic C C double bond of some (1R,3E,4S)-3-alkylidene-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones and (1R,4E,5S)-4-alkylidene-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones were studied. All additions took place predominantly from the less hindered endo-face of the methylidene compounds to give the corresponding exo-adducts as the major isomers. Thus, catalytic hydrogenations afforded the α-alkylated (1R,3R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones and (1R,4R,5R)-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones in 28–100% de. Similarly, 1,3-dipolar cycloadditions of 2,4,6-trisubstituted benzonitrile oxides gave the corresponding spiro cycloadducts in 66–100% de. The structures were determined by 2D NMR techniques, NOESY spectroscopy and X–ray diffraction.

A series of racemic dipodazine analogues 9 were prepared in 22–80% yield from (3Z,6RS)-3-[(dimethylamino)methylidene]-6-methyl-1-(phenylmethyl)piperazine-2,5-dione (7) (Scheme 1), which was prepared in four steps from (RS)-alanine methyl ester hydrochloride. The preparation of nonracemic 7 from (S)-alanine methyl ester hydrochloride failed, since the introduction of the enamino functionality at position 3 of the precursor 6 was accompanied by almost complete racemization.

N-Protected L-phenylalanines 1a,b were transformed, via the corresponding Weinreb amides 2 and ethynyl ketones 3, into chiral enamino ketones 4 (Scheme 1). Similarly, L-threonine 6 was transformed in four steps into the enamino ketone 10. Cyclocondensations of 4 and 10 with pyrazolamines 11, benzenecarboximidamide (12), and hydrazine derivatives 18 afforded N-protected 1-heteroaryl-2-phenylethanamines 15a–e, 16, 17, and 21a–k and 1-heteroaryl-1-aminopropan-2-ols 23a,b in good yields (Schemes 2 and 3). Finally, deprotection by catalytic hydrogenation furnished free amines 22a–g and 24a,b (Scheme 3).

Reductions of (1R,3R,4R)-3-([1,2,4]triazolo[4,3-x]azin-3-yl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones and their lactone analogues, prepared from (1R)-(+)-camphor, were studied. Catalytic hydrogenation selectively led to partial saturation of the [1,2,4]triazolo[4,3-x]azine residue, while in reactions with borane–methylsulfide coordination of borane to the 1-position of [1,2,4]triazolo[4,3-x]azine system took place. On the other hand, activation of the carbonyl group in (1R,3R,4R)-3-([1,2,4]triazolo[4,3-x]azin-3-yl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones with boron trifluoride etherate followed by reaction with borane–methylsulfide furnished the corresponding isoborneols, stereoselectively. The structures of all representative compounds were confirmed by X-ray diffraction.

On the basis of the enaminone methodology, libraries of 3-amino-4H-quinolizin-4-ones, fused 3-amino-4H-pyrimidin-4-ones, and fused 3-amino-2H-pyran-2-ones were synthesized by the solid-phase and by the solution-phase parallel synthesis. The solution-phase approach turned out to be advantageous over the solid-phase approach. The solution-phase synthesis afforded, in most cases, analytically pure products in high yields, whereas the solid-phase approach gave products in poor yields and in low purity.

4-[(Heteroaryldiazenyl)methylidene] and 4-([1,2,4]triazolo[4,3-x]azin-3-yl) substituted (1R,5R)-4-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones 6/6′ and 7/7′ were obtained in a one-pot transformation of the enamino lactone 2 with hydrazinoazines 3a–g followed by oxidation of the intermediate mixture of isomeric enehydrazines 4/4′ and hydrazones 5/5′ with lead tetraacetate. The oxidation selectivity was dependent on the ratio of isomeric intermediates 4/4′ and 5/5′. Treatment of 7b with lead tetraacetate led to α-acetoxylated compound 11, while bromination of 9b afforded a 1:1 mixture of α-bromination products 12 and 12′, which were separated by medium pressure liquid chromatography (MPLC). The structures of intermediates and products were confirmed by NMR and X-ray diffraction.

Methyl (2E)-3-dimethylamino-2-(1H-indol-3-yl)-propenoate was prepared simply and efficiently in two steps from 3-indoleacetic acid employing N,N-dimethylformamide dimethylacetal (DMFDMA). Upon treatment of (2E)-3-dimethylamino-2-(1H-indol-3-yl)-propenoate with various (thio)ureas in the presence of an acid 2-(1H-indol-3-yl)-3-(3-substituted(thio)ureido)propenoates were obtained in high yields. A base promoted cyclization of these (thio)ureidopropenoate derivatives afforded 5-(indol-3-yl)-3-substituted-pyrimidine-2,4-diones which represent a new family of meridianine analogues.

(1R,4E,5S)-4-Oximino-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one 9 was prepared in three steps from (1R)-(+)-camphor 1 via nitrosation of (1R,4E,5S)-4-[(dimethylamino)methylidene]-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one 8. Catalytic hydrogenation of 9 under various reaction conditions afforded (1R,4S,5S)-4-amino-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one derivatives 11, 13, and 15b. On the other hand, reduction of 9 with Grignard reagents led to two types of products, (1R,4S,5S)-4-dialkylamino-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones 15b and 15c and/or 2-substituted (1E)-1-[(1S,3R)-3-hydroxy-2,2,3-trimethylcyclopentyl]ethane-1,2-dione 1-oximes 16a,b and 15d–f. The structures of compounds 9, 10′, 15b, and 16b were determined by X-ray diffraction.

Reactions of 3-[(E)-(dimethylamino)methylidene]-(+)-camphor and (1R,5S)-4-[(E)-(dimethylamino)methylidene]-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one with hydrazine derivatives were studied. Treatment of 3-[(E)-(dimethylamino)methylidene]-(+)-camphor with hydrazines afforded the corresponding fused pyrazoles. Similarly, fused pyrazoles were obtained upon reaction of (1R,5S)-4-[(E)-(dimethylamino)methylidene]-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one with ortho-unsubstituted phenylhydrazines, while reactions with ortho-substituted phenylhydrazines and with hydrazine hydrochloride resulted in ‘ring switching’ type of transformation to furnish 2-aryl-4-[(1S,3R)-3-hydroxy-2,2,3-trimethylcyclopentyl]-1,2-dihydro-3H-pyrazol-3-ones.

Cycloadditions of (1 Z ,4 R *,5 R *)-4-benzoylamino-5-phenylpyrazolidin-3-on-1-azomethine imines to olefinic dipolarophiles were studied. Stereochemistry of cycloadditions to azomethine imines 3 was found to be controlled by stereodirecting phenyl group at position 3, as well as by the ortho -substituents at the aromatic ring at position 1′. The structures of dipoles and products were confirmed by NMR and X-ray diffraction.

Various (1R,5S)-4-[(E)-alkylidene]-1,8,8-trimethyl-2-oxabicyclo[3.2. 1]octan-3-ones were prepared, stereoselectively, via coupling of (1R,5S)-4-[(E)-(dimethylamino)methylidene]-1,8,8-tri-methyl-2-oxabicyclo[3.2.1]octan-3-one with Grignard reagents, potassium cyanide, and 2-methyl-lH-indole.

N-Substituted (1R,5S)-4-aminomethylidene-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-ones were prepared in three steps from (1R)-(+)-camphor via coupling of (1R,4E,5S)-3-[(dimethylamino)methylidene]-1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one with primary amines. N,N′-Bis-{[(1R,5S)-1,8,8-trimethyl-3-oxo-2-oxabicyclo[3.2.1]oct-4-ylidene]methyl}benzene-1,2-diamine was used as the ligand in the preparation of the corresponding coordination compounds with palladium(II), copper(II) and nickel(II). The structures were determined by 2D NMR techniques, NOESY spectroscopy and X–ray diffraction.

N-Protected (Z)-3-(arylamino)-2,3-dehydroalanine esters 5 and 10 were prepared in one step from methyl (Z)-2-acylamino-3-(dimethylamino)prop-2-enoates 3 and 9 and anilines 4 employing a parallel solution-phase synthetic approach. In most cases, analytically pure products 5 and 10 were obtained. On the other hand, a three-step parallel solid-phase synthesis of 2-acetylamino-4H-azino[1,2-x]pyrimidin-4-ones 15 via the polymer-bound methyl (Z)-2-acetylamino-3-(dimethylamino)prop-2-enoate (12) was also developped.

Benzyl (3S,4E)-4-[(dimethylamino)methylidene]-5-oxotetrahydrofuran-3-ylcarbamate 5 was prepared in 4 steps from L-aspartic acid 1. Acid-catalysed treatment of 5 with amines 6 gave the dimethylamine substitution products 7. Benzyl (3S,4E)-4-[(arylamino)methylidene]-5oxotetrahydrofuran-3-ylcarbamates 7c–n were prepared by parallel solution phase synthesis from 5 and anilines 6c–n in 45–94% yields. Enaminone 5 reacted with potassium cyanide in the presence of 18-crown-6 to afford benzyl 4-cyanomethyl-5-oxo-2,5-dihydrofuran-3-ylcarbamate 9. Upon reaction of 9 with nitrile oxide 10 the 1,2,4-oxadiazole derivative 11 was isolated in poor yield, while treatment of 9 with diazomethane 12 furnished the methylation products 13 and 14.

N3 dye molecules [cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II)] are covalently attached to boron-doped nanocrystalline diamond (B:NCD) thin films through a combination of coupling chemistries, i.e., diazonium, Suzuki, and EDC–NHS. X-ray and ultraviolet photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy are used to verify the covalent bonding of the dye on the B:NCD surface (compared to a hydrogen-terminated reference). The spectroscopic results confirm the presence of a dense N3 chromophore layer, and the positions of the frontier orbitals of the dye relative to the band edge of the B:NCD thin film are inferred as well. Proof-of-concept photoelectrochemical measurements show a strong increase in the photocurrent compared to non-dye-functionalized B:NCD films. This study opens up the possibility of applying N3-sensitized B:NCD thin films as hole conductors in dye-sensitized solar cells.

A convenient two-step sequence is presented for the conversion of ketone (I) into asymmetrically dialkylated derivatives via Wittig-type olefination followed by regioselective alkylation of the exocyclic double bond.

Donor-acceptor type light-harvesting molecular wires are covalently attached to a boron-doped diamond surface via a combination of diazonium electrografting and Suzuki cross-coupling. For the Suzuki reaction, various catalytic systems are compared with respect to their imposed surface coverage. Combining 2-dicyclohexylphosphino-2,6-dimethoxybiphenyl (SPhos) and Pd(0), the diamond coverage improves considerably (by 98%) as compared to the standard tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)(4)) catalyst. As the energy levels between the molecular chromophores and the diamond film align well, the sophisticated functionalized diamond surfaces present a first step towards the development of fully carbon-based devices for light to electricity conversion. Funding Agencies|Special Research Fund of Hasselt University; Research Foundation Flanders (FWO) [G.0555.10N]; EU FP7 Collaborative Project "MOLESOL" [256617]; Swedish Research Council Linnaeus grant; Grant Agency of the Czech Republic [13-37383S]

Ethyl (Z)-2-(2,3-dihydro-1,3-dioxo-1H-isoindol-2-yl)-3-(dimethylamino)propenoate was prepared in one step from ethyl (2,3-dihydro-1,3-dioxo-1H-isoindol-2-yl)acetate and bis(dimethylamino)-tert-butoxymethane and treated with various amines and hydrazines to afford the corresponding amino substituted products. Reactions of the titled compound with N,N'-, C,N-, and C,O'-ambident nucleophiles in refluxing acetic acid furnished the corresponding fused pyrimidinones, quinolizinones, and pyranones.

Ethyl (Z)-2-(2,3-dihydro-1,3-dioxo-1H-isoindol-2-yl)-3-(dimethylamino)propenoate was prepared in one step from ethyl (2,3-dihydro-1,3-dioxo-1H-isoindol-2-yl)acetate and bis(dimethylamino)-tert-butoxymethane and treated with various amines and hydrazines to afford the corresponding amino substituted products. Reactions of the titled compound with N,N'-, C,N-, and C,O'-ambident nucleophiles in refluxing acetic acid furnished the corresponding fused pyrimidinones, quinolizinones, and pyranones.

Two variations of a parallel solution-phase synthesis of N-substituted dimethyl 4-oxo-1,4-dihydropyridine-3,5-dicarboxylates 4 and methyl 3-oxo-3,5-dihydro-2H-pyrazolo[4,3-c]pyridine-7-carboxylates 9 from dimethyl acetone-1,3-dicarboxylate (1) were developed. The first synthetic method comprises preparation of the bis-enaminone reagents 2 and 8 and their cyclization with primary amines 3 via double substitution of both dimethylamino groups to give dihydropyridines (DHPs) 4 and 9, respectively. Another variation consists of preparation of the monoenaminone reagents 5 and 10, followed by substitution of the dimethylamino group with primary amines 3, and cyclization of the so formed intermediates 6 with N,N-dimethylformamide dimethylacetal (DMFDMA). In this manner, a library of 46 analytically pure compounds, 24 intermediates 6, 11, and 13, and 22 final dihydropyridines 4 and 9 was obtained employing just a simple filtration workup.

A simple and efficient synthesis of four new substituted pyrimidines, compounds 9a–d, from the title compound 3 is described. Conversion of 3 to methyl (E)-3-(dimethylamino)-2-(6-methoxy-2-phenylpyrimidin-4-yl)prop-2-enoate (4), followed by condensation with various dinucleophiles according to the ‘enaminone methodology’, afforded the target compounds 9 in medium-to-good yields.

Solution-phase combinatorial synthesis of (2S,4S)-4-acylamino-5-oxopyrrolidine-2-carboxamides was studied. First, di-tert-butyl (2S,4S)-4-amino-5-oxopyrrolidine-1,2-dicarboxylate hydrochloride was prepared as the key intermediate in five steps from (S)-pyroglutamic acid. Acylation of the amino group followed by acidolytic deprotection gave (2S,4S)-4-acylamino-5-oxopyrrolidine-2-carboxylic acids, which were then coupled with amines to furnish a library of (2S,4S)-4-acylamino-5-oxopyrrolidine-2-carboxamides. Four coupling reagents, BPC, EEDQ, TBTU, and PFTU, were tested for the amidation reactions in the final step. Amidations with EEDQ and TBTU led to the desired carboxamides. On the other hand, BPC and PFTU were not suited, since diketopiperazines were sometimes obtained instead of the desired carboxamides.

In this paper the regiospecific transformations of methyl 2-(benzyloxycarbonyl)amino-3-dimethylaminopropenoate (1) with hydrazine, alkyl-, aryl- and heteroaryl-substituted hydrazines via the corresponding hydrazones 12-16 into pyrazoles 17-25 are described. Heteroaryl-substitued hydrazones 13-16 afforded by oxidation with bromine or lead tetraacetate the corresponding substituted (1,2,4-triazolo[4,3-b]pyridazin-3-yl)glycinates 27-30. Alkyl 2-(2,2-disubstituted-1-ethenyl)amino-3-dimethylaminopropenoates 31-33 gave with hydrazines alkyl 2-[2,2-(disubstituted)ethenyl]amino-3-heteroarylhydrazonopropanoates 40-48 and 2-alkyl 2,3-bis((hetero)arylhydrazono)propanoates 51-55.

Substituted 2,3,5,6,7,8-hexahydropyrazolo[4,3-d][1,2]diazepine-8-carboxylates were prepared in good to excellent yields from ethyl (2E)-3-(dimethylamino)-2-{(4Z)-4-[(dimethylamino)methylidene]-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-3-yl}propenoate with 1,2-disubstituted hydrazines by heating in an alcohol.

Various aplysinopsin and β -carboline thiohydantoin analogues were prepared starting from ethyl 3-formyl-1H-indole-2-carboxylate by condensation with the active methylene group of 2-thiohydantoin, rhodanine, or thiobarbituric acid derivatives

The hydrazones 3a,b, prepared from phenylhydrazine (1) and dialkyl 2-oxopropane-1,3-dicarboxylate (2a,b) were converted in concentrated sulfuric acid at −5 °C into a mixture of alkyl (3-carboxyindol-2-yl)acetates (5a,b), and ethyl (5-ethoxy-1-phenyl-1H-pyrazol-3-yl)acetate 6. The hydrazone 8, prepared from 1 and ethyl acetoacetate (7) was transformed under the same conditions into a mixture of five compounds: ethyl 2-methylindol-3-carboxylate (9), 2-methylindol-3-carboxylic acid (10), 2-methylindol (11), 5-ethoxy-3-methyl-1-phenyl-1H-pyrazole (12), and 3-methyl-1-phenyl-1H-pyrazol-5-one (13).

(S)-3-(Dimethylamino)methylidene-5-benzyltetramic acid derivatives 4a and 4b were prepared in three steps from N-protected (S)-3-phenylalanines la and 1b, respectively. Similarly, N-[N-(benzyloxycarbonyl)glycyl]glycine (1c) was transformed into the enaminone 4c. Acid-catalysed coupling of enaminones 4a-c with aliphatic, aromatic, and heteroaromatic primary amines 5-34 afforded the corresponding N(3')-substituted 3-aminomethylidenetetramic acid derivatives 35-64 in 29-96% yields.

Various (1R,5S)-4-[(E)-alkylidene]-1,8,8-trimethyl-2-oxabicyclo[3.2. 1]octan-3-ones were prepared, stereoselectively, via coupling of (1R,5S)-4-[(E)-(dimethylamino)methylidene]-1,8,8-tri-methyl-2-oxabicyclo[3.2.1]octan-3-one with Grignard reagents, potassium cyanide, and 2-methyl-lH-indole.

[Yeap, W. S.; Bevk, D.; Vanderzande, D.; Lutsen, L.; Maes, W.; Haenen, K.] Hasselt Univ, Inst Mat Res IMO, B-3590 Diepenbeek, Belgium. [Bevk, D.; Vanderzande, D.; Lutsen, L.; Maes, W.; Haenen, K.] IMOMEC, IMEC Vzw, B-3590 Diepenbeek, Belgium. [Liu, X.; Fahlman, M.] Linkoping Univ, Dept Phys Chem & Biol, S-58183 Linkoping, Sweden. [Krysova, H.; Kavan, L.] Acad Sci Czech Republic, J Heyrovsk Inst Phys Chem, Vvi, CZ-18223 Prague 8, Czech Republic. [Pasquarelli, A.] Univ Ulm, Inst Elect Devices & Circuits, D-89069 Ulm, Germany.

The thiazolo[5,4-d]thiazole fused (bi)heterocycle is an electron deficient system with high oxidative stability and a rigid planar structure, enabling efficient intermolecular π–π overlap. The parent thiazolo[5,4-d]thiazole moiety hence already possesses some appealing features towards applications in organic electronics. Moreover, aryl-functionalized thiazolo[5,4-d]thiazole derivatives – expanding the conjugated backbone of the semiconducting material – are easily prepared. Surprisingly, interest in thiazolo[5,4-d]thiazole-based materials has been rather low, until quite recently, when the high potential of these molecules was widely recognized, notably in the field of organic photovoltaics. Despite the almost exponential growth of activity, the synthetic chemistry behind these molecules has only been explored to a minor extent and there is plenty of room for improvement and broadening of the material scope. In this review, an overview of the currently available synthetic methods and the range of materials prepared to date, together with their basic material properties and main applications, is provided, with the aim to facilitate and stimulate further progress in thiazolo[5,4-d]thiazole-based materials science.

Reaction of phenanthridinium methylides with several dipolarophiles, yielding disubstituted ylides in most of the examples, is described

1,4-Disubstituted 5-hydroxy-1H-pyrazoles (9), (12), and (13) were prepared in two steps from hydrazines (2a-k) and 3-(dimethylamino)propenoates (1), (4), and (5). First, acid-catalyzed treatment of enaminones (1), (4), and (5) with (hetero)arylhydrazines (2a-k) afforded the corresponding dimethylamine substitution products, hydrazones (3') and enehydrazines (6) and (7). Under acidic conditions, intermediates (3'), (6), and (7) did not undergo cyclization into the pyrazole derivatives. However, heating 3', 6, and 7 in a mixture of methanol and triethylamine furnished the desired products in 65-98% yields.

Methyl (E)-2-[(benzyloxycarbonyl)amino]-3-cyanopropenoate (4) was, as a versatile multifunctional reagent, transformed with hydrazine and monosubstituted aromatic and heteroaromatic hydrazines under various conditions into derivatives of pyridazine (6), pyrrole (7), imidazole-2,4-dione (9), and pyrazole (13).

The reaction of amines (4a-g) with ethyl (2E)-3-N,N-dimethylamino-2-(5-ethoxy-l-phenyl-1H-pyrazol-3-yl)propenoate (3), prepared in two steps from ethyl (4,5-dihydro-5-oxo-l-phenyl-1H-pyrazol-3-yl)acetate (1), gave ethyl (2E)-2-(5-ethoxy-1-phenyl-1H-pyrazol-3-yl)-3-(substituted amino)propenoates (5a-g). The reaction of compound (3) with 2-aminopyridine (4h), 3 amino-1H-pyrazole (4i), 2H-pyran-2-one (6a), and 5,5-dimethylcyclohexane-1,3-dione (6b) afforded 3-(pyrazol-3-yl)pyridopyrimidinone (7a), 6-(pyrazol-3-yl)pyridopyrimidinone (7b), 3-(pyrazol-3-yl)pyranopyrandione (7c), and 3-(pyrazol-3-yl)-chromenedione (7d), respectively.

Ethyl (2E)-3-dimethylamino-2-[(4Z)-4-dimethylaminomethylidene-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-3-yl]propenoate (3) was transformed with N-nucleophiles into ethyl 3-oxo-2-phenyl-3,5-dihydro-2H-pyrazolo[4,3-c]pyridine-7-carboxylates (6, 7, 9, 12, and 14).

Alkyl [(Z)-4-dimethylaminomethylidene-5-oxo-1-phenyl-4,5-dihydrolH-pyrazol-3-yl]acetate (4) was transformed with N- and C-nucleophiles into alkyl [4-(substituted amino)methylidene-4,5-dihydro-1H-pyrazol-3-yl]acetates (7) and alkyl (4-heteroarylmethylidene-4,5-dihydro-1H-pyrazol-3-yl)acetates (8), respectively. Compounds (7) cyclize by heating with DMFDMA in DMF into 2H-pyrazolo[4,3-c]pyridine-7-carboxylates (9).

A synthesis of new 2-substituted 1H-perimidines by the reaction of 1-[(methylthio)thiocarbonylmethyl]azinium salts and 1,8-diaminonaphthalene is described. Reaction of these perimidine derivatives with several electrophiles is also reported., Authors wish to thank Comision Interminlsterial de Ciencla y Tecnologia (CICYTI for financ ial support.