Synthesis of fluorine containing glycolurils and oxazolines from oxides of internal perfluoroolefins

The reaction of oxides of internal perfluoroolefins 1-3 with urea gave two kinds of novel fluorine containing N-heterocyclic compounds depending on the solvent nature: 1,5-bis(perfluoroalkyl)tetraazabicyclo[3.3.0]octane-3,7-diones 4a-c and 2-amino-5-fluoro-4,5-bis(perfluoroalkyl)-4,5-dihydrooxazol-4-ols 7a-d. Use of polar dimethylsulfoxide, N,N-dimethylacetamide and acetonitrile afforded glycolurils 4a-c in moderate yields. In dioxane, unexpected cyclization occurred resulting in oxazolines 7a-d in high yields. A similar reaction of oxiranes 2, 3 with urea in aqueous dioxane gave mixtures of 4,5-dihydroxy-4,5-bis(perfluoroalkyl)imidazolidine-2-ones 9b, c, glycolurils 4b, c and oxazolines 7b-d. The molecular structure of trans-isomers of oxazoline 7b and imidazolidine 9b has been established by X-ray crystallography.     

Silyl stabilized azanes: reactions of lithiumbis(trimethylsilyl)hydrazine with trialkyltin halides

Lithium 1,2-bis(trimethylsilyl)hydrazine (1a) reacts with Me₃SnCl, Et₃SnBr and Bu₃SnCl to form bis(trimethylsilyl)(trimethylstannyl)hydrazine (2a), (triethylstannyl)bis(trimethyl silyl)hydrazine (2b) and (tributylstannyl)bis(trimethylsilyl)hydrazine (2c), respectively. Compounds 2a and 2b undergo disproportionation at room temperature to form bis(trimethylsilyl)bis(trimethylstannyl)hydrazine (3a) and bis(triethylstannyl)bis(trimethylsilyl)hydrazine (3b). In contrast, 2c is highly stable and can withstand such a reaction up to 150 °C. The monostannylated products, 2a, 2b and 2c do not get lithiated at NH and instead undergo transmetallation in their reaction with RLi or Li to form lithiumbis(trimethylsilyl)hydrazine (1a).     

Synthesis and characterization of new soluble and thermally stable aromatic poly(amide-imide)s based on N-[3,5-bis(N-trimellitoyl)phenyl]phthalimide

A new dicarboxylic acid, N-[3,5-bis(N-trimellitoyl)phenyl]phthalimide (1a), bearing three preformed imide rings was synthesized from the condensation of N-(3,5-diaminophenyl)phthalimide and trimellitic anhydride in glacial acetic acid at 1:2 molar ratio. For study of structure-properties relationship 1,3-bis(N-trimellitoyl)benzene (1b, as a reference) was also synthesized in a similar manner. 1a and 1b were characterized by spectroscopic methods and elemental analyses.A series of wholly aromatic poly(amide-imide)s with inherent viscosities of 0.63-1.09 dl g⁻¹ was prepared by triphenyl phosphite-activated polycondensation from the triimide-dicarboxylic acid 1a and the reference monomer 1b with various aromatic diamines. All of the polymers were fully characterized by FT-IR and ¹H NMR spectroscopy. The effects of the phthalimide pendent group on the polymers properties such as solubility, crystallinity, and thermal stability were investigated by comparison of the polymers. The polymers obtained from triimide-dicarboxylic acid 1a exhibited excellent solubility in a variety of solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide. These poly(amide-imide)s possessed glass-transition temperatures from 334 to 403 °C and exhibited excellent thermal stabilities and had 10% weight losses from 541 to 568 °C under a nitrogen atmosphere. Poly(amide-imide)s containing phthalimide pendent groups showed higher solubility, higher T_g and T_d10% values than those having no phthalimide pendent groups.     

2-(1-Isopropyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyridyl transition metal (Fe, Co, and Ni) dichlorides: Syntheses, characterizations and their catalytic behaviors toward ethylene reactivity

A series of 2-(1-isopropyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyridyl metal complexes [iron (II) (1a-6a), cobalt (II) (1b-6b) and nickel (II) (1c-6c)] were synthesized and fully characterized by elemental and spectroscopic analyses. Single-crystal X-ray diffraction analyses of five coordinated complexes 5a, 3b, 5b, 1c and 2c reveal 5a and 5b as distorted trigonal-bipyramidal geometry, and 3b, 1c and 2c as distorted square pyramidal geometry. All complexes performed ethylene reactivity with the assistance of various organoaluminums. The iron complexes displayed good activities in the presence of MAO and MMAO. Upon activated by Et₂AlCl, the cobalt analogues showed moderate ethylene reactivity, while the nickel analogues exhibited relatively higher activities.     

Dinuclear rhenium(I) carbonyl complexes based on π-conjugated polypyridyl ligands with tetrathiafulvalenes: Syntheses, crystal structures, properties and DFT calculations

A series of tetrathiafulvalene-substituted 2,3-di(2-pyridyl)quinoxaline (dpq) ligands, 2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6,7-di(pyridin-2-yl)- [1,3]dithiolo[4,5-g]quinoxaline (L₁), dimethyl-2-(6,7-di(pyridin-2-yl)-[1,3]dithiolo[4,5-g]quinoxalin-2-ylidene)-1,3-dithiole-4,5-dicarboxylate (L₂), and 2-(5,6-dihydro-[1,3]dithiolo[4,5-b] [1,4]dithiin-2-ylidene)-6,7-di(pyridin-2-yl)-[1,3]dithiolo[4,5-g]quinoxaline (L₃), have been prepared. Reactions of these ligands with Re(CO)₅Cl afford the corresponding dinuclear rhenium(I) carbonyl complexes, Re₂(L)(CO)₆Cl₂ (L = L₁, 5a; L = L₂, 5b; L = L₃, 5c). All new compounds are fully characterized by ¹H NMR, IR and mass spectroscopies. The crystal structures of 5a and 5b have been studied. Optimized conformations and molecular orbital diagrams of 5a−5c have been calculated with density functional theory (DFT). The spin-allowed singlet−singlet electronic transitions of all complexes have been calculated with time-dependent DFT (TDDFT), and the UV-Vis−NIR spectra are discussed based on the theoretical calculations.     

Complexing properties of two benzocrown-ether moieties arranged at a cyclobutane ring system

Biscrown ethers 2a-c and 3a-c arranged at a cyclobutane ring were prepared by intermolecular [2+2] photocycloaddition of vinylated benzocrown ethers. The complexing behavior of 2a-c toward alkali metal cations was evaluated by ESI-MS analysis, liquid-liquid extraction, and the comparison of complexing stability constant. An intramolecular sandwich-type 1:1 (host/guest) complexation was observed by ESI-MS analysis in the competitive system where 2a-Na⁺, 2b-K⁺, and 2c-Cs⁺ were formed selectively. In the liquid-liquid extraction, however, 2a hardly extracted any cation, while both 2b and 2c efficiently extracted larger cations such as K⁺, Rb⁺, and Cs⁺. It was found that the complexing stability constant of 2a-Na⁺ is lower than that of benzo-15-crown-5-Na⁺ though extraordinarily high values were obtained for 2b-K⁺ and 2c-Cs⁺ complexes compared with those of 18-crown-6-K⁺ and dibenzo-24-crown-8-Cs⁺ complexes, respectively. Hence, the excellent complexing ability was achieved by using the cyclobutane ring, which strongly preorganized two benzocrown-ether moieties for the larger alkali metal cations.     

1,1,3,3,3-Pentafluoro-2-pentafluorophenyl-1,2-epoxypropane and trimethylphosphite: unusual 1,4-dioxan-2,5-dione ring formation

1,1,3,3,3-Pentafluoro-2-pentafluorophenyl-1,2-epoxypropane 1 reacted with trimethylphosphite giving two diastereomers, (Z)- and (E)-3,6-bis(trifluoromethyl)-3,6-bis(pentafluorophenyl)-1,4-dioxan-2,5-dione 2a, b in a 1:1 ratio, cyclodimerisation product of the intermediately generated α-lactone 4. Compounds 2a, b were hydrolysed to furnish 3,3,3-trifluoro-2-hydroxy-2-(2,3,4,5,6-pentafluorophenyl)propionic acid 5.     

Microwave-assisted synthesis of novel bis(2-thioxothiazolidin-4-one) derivatives as potential GSK-3 inhibitors

(5Z,5′Z)-3,3′-(1,4-Phenylenebis(methylene)-bis-(5-arylidene-2-thioxothiazolidin-4-one) derivatives (5a-r) have been synthesized by the condensation reaction of 3,3′-(1,4- or 1,3-phenylenebis(methylene))bis(2-thioxothiazolidin-4-ones) (3a,b) with suitably substituted aldehydes (4a-f) or 2-(1H-indol-3-yl)2-oxoacetaldehydes (8a-c) under microwave conditions. The bis(2-thioxothiazolidin-4-ones) were prepared from the corresponding primary alkyl amines (1a,b) and di-(carboxymethyl)-trithiocarbonyl (2). The 2-(1H-indol-3-yl)-2-oxoacetaldehydes (8a-c) were synthesized from the corresponding acid chlorides (7a-c) using HSnBu₃.     

Synthesis of novel lariat azathia crown macrocycles containing two triazole rings and bis crown macrocycles containing four triazole rings

The 13-hydroxy macrocycles 7a-d were prepared in 40-50% yields by the condensation of 1,ω-bis(4-amino-1,2,4-triazol-3-ylsulfany)alkanes 2a-d with 1,3-bis(2-formyphenoxy)-2-propanol (9). Acylation of 7a-d with 2-chloroacetylchloride gave the corresponding esters 11a,b. Amination of 11a,b with different amines in acetone furnished exclusively the target lariat macrocycles 12a,b and 13 in 60-70% yields. Reaction of 2 equiv. of the macrocycles 11a,b with 1 equiv. of piperazine afforded the novel bis macrocyles 14a,b in 50-60% yields. Reduction of 7a-d with NaBH₄ afforded the corresponding 13-hydroxyazathia crown ethers 15a-d in 65-70% yields.     

Green diastereoselective synthesis of highly functionalised trifluoromethylated γ-lactone phosphonate esters bearing a thioester or ketothiophene

A facile diastereoselective synthesis of highly functionalised 3-(1-diphenylphosphonylethyl)butyrolactone analogues, 3a-c is achieved from the reaction of dialkyl acetylenedicarboxylates, 2a,b, with thiolated and trifluoromethylated-1,3-diones, CH acids, 1a,b, in the presence of triphenyl phosphite. The resulting products, 3a-c, are obtained in high yields and characterised by ¹H/¹³C, ¹⁹F, ³¹P NMR and X-ray crystallography.     

Gold(I) N-heterocyclic carbene based initiators for bulk ring-opening polymerization of l-lactide

Synthesis, structures, and catalysis studies of gold(I) complexes of N-heterocyclic carbenes namely, a di-O-functionalized [1-(2-hydroxy-cyclohexyl)-3-(acetophenone)imidazol-2-ylidene], a mono-O-functionalized [1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazol-2-ylidene] and a non-functionalized [1,3-di-i-propyl-benzimidazol-2-ylidene], are reported. Specifically, the gold complexes, [1-(2-hydroxy-cyclohexyl)-3-(acetophenone)imidazol-2-ylidene]AuCl (1c), [1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazol-2-ylidene]AuCl (2c), and [1,3-di-i-propyl-benzimidazol-2-ylidene]AuCl (3b), were prepared from the respective silver complexes 1b, 2b, and 3a by treatment with (SMe₂)AuCl in good yields following the commonly used silver carbene transfer route. The silver complexes 1b, 2b, and 3a were synthesized from the respective imidazolium halide salts by the reactions with Ag₂O. The N-heterocyclic carbene precursors, 1-(2-hydroxy-cyclohexyl)-3-(acetophenone)imidazolium chloride (1a) and 1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazolium chloride (2a), were synthesized by the direct reactions of cyclohexene oxide and imidazole with chloroacetophenone and benzyl chloride respectively. The gold (1c, 2c, and 3b) and the silver (3a) complexes along with a new O-functionalized imidazolium chloride salt (1a) have been structurally characterized by X-ray diffraction. The structural studies revealed that geometries around the metal centers were almost linear in these gold and silver complexes. The gold (1c, 2c, and 3b) complexes efficiently catalyze ring-opening polymerization (ROP) of l-lactide under solvent-free melt conditions producing polylactide polymer of moderate to low molecular weights with narrow molecular weight distributions.     

A general method for the synthesis of the most powerful naturally occurring Maillard flavors

The natural flavors 2-acetyl-1-pyrroline 1a, 2-propionyl-1-pyrroline 1b, 2-acetyl-3,4,5,6-tetrahydropyridine 1c, 2-acetyl-2-thiazoline 1d, 2-propionyl-2-thiazoline 1e, and the artificial flavor 2-acetyl-5,6-dihydro-4H-1,3-thiazine 1f have been prepared by catalytic SeO₂ oxidation of the corresponding cyclic imines 6a-c and sulfur cyclic imines 7a-c using TBHP as co-oxidant. The oxidation of the pyrrolines 1a and b is completely regioselective. Professional olfactory evaluation together with the odor threshold of the new flavor 1f is reported.     

Thermal and photochemical isomerization of exocyclic 1,3-dienes: 1,1-diphenyl-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane s-cis(E,E)

This paper describes the photochemical and the thermal isomerization of s-cis(E,E) 1,1-diphenly-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane (1a). Under thermal conditions a 1,3-sigmatropic of the methylene hydrogen occurs, yielding the s-trans isomer (1b). The photochemical irradiation of (1a) at 300 nm for 1 h in deoxygenated benzene gives the corresponding s-cis(E,Z) isomer (1c) and then the s-cis(Z,Z) isomer (1d) after prolonged irradiation (3 h). There was no evidence for the formation of the corresponding cyclobutene resulting from the ring closure of the exocylic diene.     

Molecules to supermolecules and self assembly: a study of some cocrystals of cyanuric acid

The preparation and structure elucidation of cocrystals 1a, 1b, 2a-4a, formed from cyanuric acid (CA) and the aza-donor compounds 4,7-phenanthroline, 1,7-phenanthroline, phenazine and 1,3-bis(4-pyridyl)propane, respectively, have been reported. While CA forms different types of self-assembling modes—monomers (1a), dimers (1b and 4a) and infinite tapes (2a and 3a)—the recognition of the constituents, however, is through a triple hydrogen-bonding pattern, consisting of an N-H?N and two C-H?O hydrogen bonds, except in 4a.     

Synthesis of imidazo[5,1-b]thiazoles or spiro-β-lactams by reaction of imines with mesoionic compounds or ketenes generated from N-acyl-thiazolidine-2-carboxylic acids

New mesoionic compounds (2H, 3H-thiazolo[3,2-c]oxazol-7-ones) (β) or ketenes ((3-acyl-1,3-thiazolidin-2-ylidene)methanone) (β′) were generated from N-acetyl and N-benzoyl-thiazolidine-2-carboxylic acids (7a,b) using different methods, and their reactivity towards N-(phenylmethylene)benzenesulfonamide (2) and N-(phenylmethylene)aniline (3) was tested. When (7a,b) were treated with (2) and acetic anhydride in refluxing toluene solution, only imidazo[5,1-b]thiazoles (8a,b) were obtained from the mesoionic compound intermediates (β). When the ketene intermediates (β′) were generated from (7a,b) by means of Mukaiyama's reagent, only spiro-β-lactams (9a,b) were isolated.     

Platinum-catalyzed double silylations of alkynes with bis(dichlorosilyl)methanes

Bis(dichlorosilyl)methanes 1 undergo the two kind reactions of a double hydrosilylation and a dehydrogenative double silylation with alkynes 2 such as acetylene and activated phenyl-substituted acetylenes in the presence of Speier’s catalyst to give 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes 4 as cyclic products, respectively, depending upon the molecular structures of both bis(dichlorosilyl)methanes (1) and alkynes (2). Simple bis(dichlorosilyl)methane (1a) reacted with alkynes [R¹-CC-R²: R¹ = H, R² = H (2a), Ph (2b); R¹ = R² = Ph (2c)] at 80 °C to afford 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 as the double hydrosilylation products in fair to good yields (33-84%). Among these reactions, the reaction with 2c gave a trans-4,5-diphenyl-1,1,3,3-tetrachloro-1,3-disilacyclopentane 3ac in the highest yield (84%). When a variety of bis(dichlorosilyl)(silyl)methanes [(Me_nCl_3 − nSi)CH(SiHCl₂)₂: n = 0 (1b), 1 (1c), 2 (1d), 3 (1e)] were applied in the reaction with alkyne (2c) under the same reaction conditions. The double hydrosilylation products, 2-silyl-1,1,3,3-tetrachloro-1,3-disilacyclopentanes (3), were obtained in fair to excellent yields (38-98%). The yields of compound 3 deceased as follows: n = 1 > 2 > 3 > 0. The reaction of alkynes (2a-c) with 1c under the same conditions gave one of two type products of 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes (4): simple alkyne 2a and terminal 2b gave the latter products 4ca and 4cb in 91% and 57% yields, respectively, while internal alkyne 2c afforded the former cyclic products 3cc with trans form between two phenyl groups at the 3- and 4-carbon atoms in 98% yield, respectively. Among platinum compounds such as Speier’s catalyst, PtCl₂(PEt₃)₂, Pt(PPh₃)₂(C₂H₄), Pt(PPh₃)₄, Pt[ViMeSiO]₄, and Pt/C, Speier’s catalyst was the best catalyst for such silylation reactions.     

Stereocontrolled conversion of some optically active (4S,5R)-dihydroisoxazoles into acyclic 3-acetamido-1,2-diols

Optically active (4S,5R)-dihydroisoxazoles 5a-c (90-91% ee) have been prepared by reaction of the epoxyketones 4a-c with hydroxylamine. Reduction of compounds 5a and 5b using lithium aluminium hydride took place exclusively from the Re face to give (1R,2S,3S)-1,3-disubstituted-3-aminopropane-1,2-diols 6a and 6b. These amino-diols were characterised by N-acetylation and the stereochemical sense of the hydride reduction was confirmed by conversion of amides 7a and 7b into α-amino acid derivatives 10a and 10b.     

Addition of silyloxydienes to 2,6-dibromo-1,4-benzoquinone: an approach to highly oxygenated bromonaphthoquinones for the synthesis of thysanone

The synthesis of tetraoxygenated bromonaphthoquinones 6a, 6b, 6c, 6d, key intermediates for a synthesis of the 3C protease inhibitor, thysanone, were investigated. Addition of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadiene 8 to 2,6-dibromo-1,4-benzoquinone 10 in benzene afforded a mixture of naphthoquinone 6a, arising from Diels-Alder addition followed by aromatisation, and Michael adduct 12. The Michael adduct 12 predominated when THF was used as solvent whereas 6a predominated when benzene was used. Naphthoquinone 6a underwent benzylation to naphthoquinone 6c. Addition of 1,1-dimethoxy-3-trimethylsilyloxy-1,3-butadiene 9 to 2,6-dibromo-1,4-benzoquinone 10 followed by benzylation failed to afford the desired bromonaphthoquinone 6d yet methylation did afford naphthoquinone 6b. Bromonaphthoquinone 6d was finally prepared from naphthol 18, obtained from addition of diene 9 to 1,4-benzoquinone 17, followed by ortho-bromination and oxidation. Attempted Sakurai allylation of bromonaphthoquinone 6d afforded naphthodihydrofuran 21. A similar observation was observed for 2-carbomethoxy-1,4-naphthoquinone 22 that also underwent Sakurai allylation to afford naphthodihydrofuran 23. The structure of Michael adduct 12 was confirmed by X-ray crystallography.     

Rapid syntheses of (±)-pterocarpans and isoflavones via the gold-catalyzed annulation of aldehydes and alkynes

(±)-Pterocarpan and analogues (4a-c) have been synthesized efficiently via the annulation of salicylaldehydes (1a, 1b and 1c) and o-methoxymethoxylphenylacetylene (2a), followed by a one-pot reduction and acidic cyclization of the ketones (3a-c). In addition, isoflavone derivatives (5a-c) have been synthesized rapidly, in two steps, via the annulation of salicylaldehyde (1a) and arylacetylenes (2b, 2c and 2d), followed by IBX/DMSO oxidation of the isoflavanones (3d, 3e and 3f).