An expedient method for the synthesis of 6-substituted uracils under microwave irradiation in a solvent-free medium

Condensation of malonic acid 1 and ureas 2a-f proceeds smoothly in the presence of acetic anhydride 3 under microwave irradiation in solvent-free conditions to give 6-hydroxy-uracils 4 in excellent yields. Under identical conditions, the condensation of cyanoacetic acid 5 and ureas 2a,b,g and h in the presence of acetic anhydride 3, followed by cyclization in the presence of sodium hydroxide affords 6-amino-uracils 6 in high yields. The work-up procedures are simple and products need no purification.     

Improved enamine-type addition of dehydroaporphine using microwave irradiation

Previous report demonstrated that 7-substituted aporphine, possessing interesting biological aspects, could be synthesized via an enamine-type addition of dehydroaporphine reacted with an electrophile, but it has the drawbacks of a long reaction time, low yield, and limitation to reactive electrophiles. Here we found that the reaction time and yield could greatly be improved under microwave irradiation in the presence of 4 equiv of sodium iodide for the synthesis of 7-benzyl dehydroglaucine. The application of this finding for treating dehydroglaucine with a variety of alkyl bromides also gave corresponding 7-substituted dehydroglaucines (2a-j) with yields of 14-89%. Other enamines such as 1,10-dimethoxydehydroaporphine (3a), 2,9-diacetyldehydroboldine (3b), and 7,8-dihydroberberine (5) were found to react with benzyl bromide under similar conditions as described above to give corresponding products (4a-b, 6) in satisfactory yields, indicating the versatility of this improved reaction condition.     

Michael monoadditions of nitromethane or nitroethane with electrophilic gem-disubstituted alkenes over alumina under microwave irradiation

Nitromethane 1a or nitroethane 1b react with electrophilic alkenes 2a-i RCHC(CN)(Y) with Y=CO₂R′, CN, CONH₂ adsorbed on alumina to give selectively at room temperature or under focused microwave irradiation new Michael monoadducts 5 (two diastereoisomers) or 6 (four diastereoisomers) after a few minutes. It is possible to obtain only two diastereoisomers of 6 by reaction of the corresponding nitroalkene and methylcyanoacetate in the presence of catalytic amounts of piperidine. Mechanisms are proposed. Some examples of addition of nitroalkanes with electron-deficient alkynes in dry media coupled with microwave irradiation conditions are also described.     

Synthesis of allenes via CuBr-catalyzed homologation of alk-1-ynes accelerated by microwave

CuBr-catalyzed homologation of alk-1-ynes 1 with paraformaldehyde and N,N-diisopropylamine (or N,N-dicyclohexylamine) was accelerated by microwave irradiation at 150 °C to afford the corresponding allenes 2 in good to high yields in 1-10 min. Bisalkynes 5 and 7 were also converted to the corresponding bisallenes 6 and 8 in 63% and 61% yields, respectively, under the current condition.     

Regioselective addition of Grignard reagents to 2,6-dicyanoanilines and cyclization to new quinazoline derivatives under thermal/microwave irradiation conditions

Two strategies have been developed for the synthesis of novel quinazoline derivatives. 2,6-Dicyanoanilines were reacted with Grignard reagents followed by cyclization to give two quinazoline regioisomers 2 and 3. Alternately 2,6-dicyanoanilines on reaction with Grignard reagents gave imine regioisomers 4 and 5. Each imine regioisomer was separated and independently cyclized to give new quinazoline derivatives 6, 7 and 8, 9, respectively, under different microwave irradiation conditions.     

Solvent-free synthesis of novel unsymmetric chenodeoxycholic acid bis thiocarbazone derivatives promoted by microwave irradiation and evaluation of their antibacterial activity

Eleven new non-symmetric chenodeoxycholic acid bis thiocarbazones were efficiently synthesized via the condensation of steroidal diketones (methyl (5β)-3,7-dioxocholan-24-oate) and substituted benzaldehyde thiocarbohydrazones by means of microwave irradiation. Compared with the conventional heating method, the yields were increased from 31–58% to 80–89% and the reaction times were reduced from 420–520 min to 5.0–7.5 min. The structures of these novel compounds were characterized by spectral data and elemental analysis. Four compounds (7a, 7c, 7f and 7g) possess excellent activity against Bacillus subtilis and Staphylococcus aureus.     

Rhodium-catalyzed intermolecular hydroacylation of 1-alkynes: Effect of phosphines and MK-10 on the reaction selectivity

The use of bulky ligands in the rhodium-catalyzed reaction of aldehydes 7 (R¹ = Ph) and 18 with 1-octyne increased the selectivity for ketones 13 and 20, to the detriment of ketones 12 and 19. Bulky phosphines reduced the hydroacylation reaction rate, leading to competition from the addition of the benzoic acid co-catalyst to the alkynes. This competing reaction can be suppressed by using the clay Montmorillonite K 10 (MK-10) as the co-catalyst instead of benzoic acid.     

Thermal and microwave assisted reactions of 2,5-disubstituted thienosultines with [60]fullerene: non-Kekulé biradicals and self-sensitized oxygenation of the cycloadduct

Refluxing an o-dichlorobenzene solution of 2,5-disubstituted thienosultines 10a-f with [60]fullerene for 2-24 h gave both 1:1 and 2:1 cycloadducts in 37-79% isolated yields. The reaction was highly accelerated by microwave irradiation giving comparable yields of cycloadducts. Sultines 10a-f underwent cheletropic extrusion of SO₂ to form the corresponding non-Kekulé biradical intermediates 11a-f, which were subsequently trapped by [60]fullerene to form corresponding cycloadducts. The activation energy barriers (ΔG_c^≠) determined for the boat-to-boat inversion of these 4′,5′,6′,7′-tetrahydrobenzo[c]thieno-[5′,6′:1,2][60]fullerene adducts 12a-f were found to be in the range of 13.5-14.8 kcal/mol. Unexpectedly, one of the monoadduct 12a was found to be labile when kept in air under ambient light. Two new products 15 (a sulfine-enone) and 16 (an endione) were isolated from the decomposed 12a and were found to derive from self-sensitized singlet oxygen reaction on the 2,5-dimethylthieno moiety of 12a.     

Solvent-free one-pot reactions for annulating a pyrimidine ring on thiazoles under microwave irradiation

One-pot reactions of glycine, acetic anhydride and thiazole Schiff bases (2a-f) diastereoselectively and expeditiously annulate a pyrimidine ring on the thiazole nucleus to yield 6,7-dihydro-5H-thiazolo[3,2-a]pyrimidin-5-ones (4a-f) under microwave irradiation and solvent-free conditions.     

The synthesis, using microwave irradiation and characterization of novel, metal-free and metallophthalocyanines

The synthesis of novel metal-free (4) and metallophthalocyanines (5, 6, 7 and 8) were prepared by cyclotetramerization of a novel 4-[2-(1-naphthyloxy)ethoxy]phthalonitrile (3). New substitute phthalocyanines showed the enhanced solubility in organic solvents. The new compounds were characterized by a combination of IR, ¹H NMR, ¹³C NMR, UV-Vis and MS spectral data.     

Muchimangins E and F: novel diphenylmethyl-substituted xanthones from Securidaca longepedunculata

Two new highly oxygenated xanthones, named muchimangins E (1) and F (2), have been isolated from the root of Securidaca longepedunculata (Polygalaceae). Their structures were elucidated by the analyses of spectral data to be a novel xanthone with a diphenylmethyl substituent at C-2. Moreover, the structures of muchimangins B (4) and C (5) were revised by careful analysis of the spectral data and by comparing their NMR data with those of 1 and 2, to be xanthones with the diphenylmethyl substituent at C-2, not at C-4 reported previously.     

Regioselective aminoethylation of 1,4-benzodiazepin-2-one under conventional heating and microwave irradiation

The regioselective aminoethylation of 1,4-benzodiazepin-2-one 1 can be carried out using classical heating or microwave irradiation as the source of energy to furnish either N-1 or N-4 aminoethylated products 2a-d and 3a-d, respectively. The regioselectivity observed has been rationalized using computational studies and has been traced to the disparity of the rate-determining steps along the N-1 product (N-1 PR) and N-4 product (N-4 PR) formation pathways.     

Investigations on synthesis of indole based constrained mimetic scaffolds through 1,3-dipolar cycloadditions of the C-(3-indolyl)-N-phenylnitrone with a variety of olefinic and allenic dipolarophiles under microwave irradiation

Monomode microwave assisted regio- and stereo-selective 1,3-dipolar cycloadditions of C-(3-indolyl)-N-phenylnitrone (19) with a number of olefinic dipolarophiles (20a-f) afford isoxazolidines (21-26) in high yields, which are conformationally constrained mimetics of indole-3-propionic acid of biological significance. Similar cycloadducts derived from addition of nitrone (19) to allenic esters (27a-c) undergo domino reorganization to afford potentially biologically active bis-indole derivatives (28, 29). The observed regio- and stereo-selectivities are analysed, inter alia, in terms of HOMO-dipole-LUMO-dipolarophile and involved secondary orbital/steric interactions in the transition states intervening these cycloadditions.     

Studies on inverse electron demand hetero Diels-Alder reaction of perfluoroalkyl 2(1H) pyridones with different dienophiles under microwave irradiation

The reaction of N-acetyl perfluoroalkyl substituted 2(1H) pyridones (7) with dimethylacetylenedicarboxylate (DMAD) on neutral alumina under solvent free microwave irradiation conditions extended to undergo an inverse electron demand hetero Diels-Alder reaction, however resulted exclusively in E, Z isomers (3:1) of Michael-type N-adducts (8). The similar reaction in case of 7a under thermal and photochemical conditions also gave the same products.     

Synthesis and properties of new poly(ether-ester)s containing aliphatic diol based on isosorbide. Effects of the microwave-assisted polycondensation

Microwave irradiation was applied to synthesize to the bulk synthesis of novel poly(ether-ester)s based on diol-ether of isosorbide (1) and adipoyl chloride (2) or terephthaloyl chloride (3). Thus, the poly(ether-ester)s (4 and 5) consist partially of isosorbide. In order to check the influence of microwaves and possible specific non-thermal microwave effects, the reactions were comparatively performed inside a thermostated oil bath under similar conditions. The reaction conditions were varied to optimize both yields and molecular weights of poly(ether-ester)s. The reaction proceeded roughly five times faster under microwave irradiation, the polycondensation being almost completed (yields upto approximately 95%) within 5 min to afford a series of novel poly(ether-ester)s based with relatively high average molecular weights (M_w upto approximately 8000). The resulting poly(ether-ester)s were characterized by NMR (¹H and ¹³C), FT-IR spectrometry, SEC measurements and MALDI-TOF mass spectrometry. Thermal properties of the poly(ether-ester)s (4 and 5) were investigated by means of differential scanning calorimetry (DSC).     

A novel metal-free and metallophthalocyanines containing four 19-membered dithiadiazadioxa macrocycles by microwave irradiation: Synthesis and characterization

The novel tetrasubstituted metal-free phthalocyanine (5) and metallophtalocyanines (6, 7 and 8) bearing four 19-membered dithiadiazadioxa macrocyclic moieties on peripheral positions have been synthesized by cyclotetramerization reaction of phthalonitrile derivative (4) in a multi-step reaction sequence. The new compounds were characterized by a combination of IR, ¹H NMR, ¹³C NMR, UV-Vis, elemental analysis and MS spectral data.     

Proteasome-inhibitory and cytotoxic constituents of Garcinia lateriflora: absolute configuration of caged xanthones

A new biflavonoid (1), a new xanthone enantiomer (2), five new caged xanthones (3-7), and several known compounds were isolated from the stem bark of Garcinia lateriflora, collected in Indonesia. The structures of the new compounds were determined by analysis of spectroscopic data, and the absolute configuration of the caged xanthones was shown for the first time at carbons 5, 7, 8, 8a, 10a, and 27, by analysis of COSY and NOESY NMR and ECD spectra. The biflavonoids exhibited proteasome-inhibitory activity, and the known compound, morelloflavone (8) was found to have the greatest potency (IC₅₀=1.3 μM). The caged xanthones were cytotoxic toward HT-29 cells, with the known compound, morellic acid (10) being the most active (ED₅₀=0.36 μM). However, when tested in an in vivo hollow fiber assay, it was inactive at the highest dose tested (20 mg/kg).     

Microwave-assisted synthesis and characterization of a new soluble metal-free and metallophthalocyanines peripherally fused to four 18-membered tetrathiadiaza macrocycles

Preparation of some novel symmetrically tetrasubstituted metal-free phthalocyanine (6) and metallophthalocyanines (7-10) containing four 18-membered tetrathiadiaza macrocycles moieties on peripheral positions has been achieved by cyclotetramerization reaction of phthalonitrile derivative (5) in a multi-step reaction sequence. Metal-free phthalocyanine (6) was synthesized by microwave irradiation of 13,24-bis[(4-methylphenyl)sulfonyl]-6,7,14,15,23,24-hexahydro-13H,22H-tribenzo[b,h,n][1,4,10,13,7,16]tetrathiadiazacyclo-octadecine-18,19-dicarbonitrile (5) in 2-(dimethylamino)ethanol. The metallophthalocyanines (7-10) were prepared by the reaction of the phthalonitrile compound (5) with NiCl₂, Zn(CH₃COO)₂, CoCl₂, CuCl₂ salts, respectively, by microwave irradiation in 2-(dimethylamino)ethanol for at 175 °C, 350 W. The new compounds were characterized by IR, ¹H NMR, ¹³C NMR, UV-Vis, elemental analysis and MS spectra data.     

Synthesis,photophysical and nonlinear optical properties of microwave synthesized 4-tetra and octa-substituted lead phthalocyanines

This work presents the photophysical and nonlinear optical behaviour of newly synthesized complexes: 2,(3)-tetrakis(4-benzyloxyphenoxyphthalocyaninato) lead (5a) and 2,3-octakis(4-benzyloxyphenoxyphthalocyaninato) lead (6a). The nonlinear optical behaviour of complexes 5a and 6a are compared with those of 2,(3)-tetraphenoxyphthalocyaninato lead (5b), 2,(3)-tetrakis(4-t-butylphenoxyphthalocyaninato) lead (5c), 2,3-octaphenoxyphthalocyaninato lead (6b) and 2,3-octakis(4-t-butylphenoxyphthalocyaninato) lead (6c). The synthesis of 5a and 6a was performed using microwave irradiation. Photophysical properties were studied for these complexes in dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.80 to 0.86 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and <10 μs in the rest of the solvents) were observed due to the presence of heavy atom. Nonlinear optical properties were studied in dimethylsulfoxide. The optical limiting threshold intensity (I_lim) for the PbPc derivatives were calculated and ranged from 2.1 to 6.6 W/cm².     

Novel optically active poly(amide-imide)s from N,N-(4,4-carbonyldiphthaloyl)-bis-l-phenylalanine diacid chloride and aromatic diamines by microwave irradiation

3,3^′,4,4^′-benzophenonetetracarboxylic dianhydride (4,4^′-carbonyldiphthalic anhydride) (1) was reacted with l-phenylalanine (2) in a mixture of acetic acid and pyridine (3:2) and the resulting imide-acid [N,N^′-(4,4^′-carbonyldiphthaloyl)-bis-l-phenylalanine diacid] (4) was obtained in high yield. The compound (4) was converted to the N,N^′-(4,4^′-carbonyldiphthaloyl)-bis-l-phenylalanine diacid chloride (5) by reaction with thionyl chloride. A new facile and rapid polycondensation reaction of this diacid chloride (5) with several aromatic diamines such as 4,4^′-diaminodiphenyl methane (6a), 2,4-diaminotoluene (6b), 4,4^′-sulfonyldianiline (6c), p-phenylenediamine (6d), 4,4^′-diaminodiphenylether (6e), m-phenylenediamine (6f), benzidine (6g) and 2,6-diaminopyridine (6h) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol. The polymerization reactions proceeded rapidly, compared with the conventional solution polycondensation, and was completed within 7 min, producing a series of optically active poly(amide-imide)s with high yield and inherent viscosity of 0.22-0.52 dl/g. All of the above polymers were fully characterized by IR, elemental analyses and specific rotation. Some structural characterization and physical properties of this optically active poly(amide-imide)s are reported.