17α-Konfigurierte 20-methylpregnan-derivate

A mixture of 1a+1b (17α), obtained by C-17-epimerization of pregnenolone (1a) was converted into 3a+3b by Wittig-reaction. 3a+3b were acetylated to a mixture of 4a+4b, from which 4b was isolated by cristallization of 3a and following AgNO₃-chromatography of the mother-liquors. Δ²⁰⁽²²⁾ → Δ¹⁷-doublebond-isomerization occurs by hydrogenation (Pd/C) of 3a (17β) to give 5. Hydrogenation (Pt-catalyst) of 4b (17α) leads to 8b, which was converted into the 20-methylpregnane-derivatives 7b, 9b–13b. By comparison with the 17β epimers 1a–4a, 7a–13a a spectroscopic determination of the relative configuration on C-17 of 17-alkylsubstituted steroids was possible.     

Palladium complexes of 8-(di-tert-butylphosphinooxy) quinoline

The preparation of the new ligand 8-(di-tert-butylphosphinooxy)quinoline (1) and the palladium derivatives [PdCl₂(1)] (2), [Pd(η³-all)(1)]⁺ [all = C₃H₅ (3a), 1-PhC₃H₄ (3b) and 1,3-Ph₂C₃H₃ (3c)] and [Pd(η²-ol)(1)] [ol = dimethyl fumarate (4a) and fumaronitrile (4b)] is reported. The cationic species 3a-3c have been isolated as salts. The complex 3a(BF₄) is obtained either from the reaction of 1 with [Pd(μ-Cl)(η³-C₃H₅)]₂ or from the reaction of ClP(CMe₃)₂ with [Pd(η³-C₃H₅)(8-oxyquinoline)], followed in both cases by chloride abstraction with NaBF₄. In the complexes, the ligand 1 is P,N chelated to the central metal, as shown by the X-ray structural analysis of 3a(BF₄). At 25 °C in solution, 3a(BF₄) and 3b(BF₄) undergo a fast η³−η¹−η³ dynamic process which brings about a syn-anti exchange only for the allylic protons cis to phosphorus, while for 4a and 4b a slow rotation of the olefin around its bond axis to palladium takes place. The complexes 2 and 3a(BF₄) are efficient catalyst precursors in the coupling of the phenylboronic acid with aryl bromides and chlorides.     

Synthesis, properties, and oxidizing function of 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates

Uracil-annulated heteroazulenes, 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates 7a,b·BF₄⁻, which are the isoelectronic compounds of 5-dezazaflavin, were synthesized. X-Ray crystal analysis and MO calculations were carried out to clarify the structural characteristics of 7a,b·BF₄⁻. The stability of cations 7a,b is expressed by the pK_R+ values which were determined spectrophotometrically to be 10.9 and 11.2, respectively. The electrochemical reduction of 7a,b exhibited high reduction potentials at −0.84 and −0.87 (V vs Ag/AgNO₃) upon cyclic voltammetry (CV). A good linear correlation between the pK_R+ values and reduction potentials (E1_red) of 7a,b·BF₄⁻ and reference compounds 4·BF₄⁻ and 5·BF₄⁻ was obtained. In a search of the reactivity, reactions of 7a,b·BF₄⁻ with some nucleophiles, hydride and diethylamine, were carried out to clarify that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of 7a,b·BF₄⁻ toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compounds 7a,b·BF₄⁻], suggesting the oxidizing function of 7a,b·BF₄⁻ toward alcohols in the autorecycling process.     

Five-coordinate pentafluorobenzothiolate osmium(IV) complexes [Os(SC6F5)4(P(C6H4X-4)3)] (X = OCH3, CH3, F, Cl or CF3): Solid and solution structural characterization

The reactions of OsO₄ with excess of HSC₆F₅ and P(C₆H₄X-4)₃ in ethanol afford the five-coordinate compounds [Os(SC₆F₅)₄(P(C₆H₄X-4)₃)] where X = OCH₃ 1a and 1b, CH₃ 2a and 2b, F 3a and 3b, Cl 4a and 4b or CF₃ 5a and 5b. Single crystal X-ray diffraction studies of 1 to 5 exhibit a common pattern with an osmium center in a trigonal-bipyramidal coordination arrangement. The axial positions are occupied by mutually trans thiolate and phosphane ligands, while the remaining three equatorial positions are occupied by three thiolate ligands. The three pentafluorophenyl rings of the equatorial ligands are directed upwards, away from the axial phosphane ligand in the arrangement “3-up” (isomers a). On the other hand, ³¹P{¹H} and ¹⁹F NMR studies at room temperature reveal the presence of two isomers in solution: The “3-up” isomer (a) with the three C₆F₅-rings of the equatorial ligands directed towards the axial thiolate ligand, and the “2-up, 1-down” isomer (b) with two C₆F₅-rings of the equatorial ligands directed towards the axial thiolate and the C₆F₅-ring of the third equatorial ligand directed towards the axial phosphane. Bidimensional ¹⁹F–¹⁹F NMR studies encompass the two sub-spectra for the isomers a (“3-up”) and b (“2-up, 1-down”). Variable temperature ¹⁹F NMR experiments showed that these isomers are fluxional. Thus, the ¹⁹F NMR sub-spectra for the “2-up, 1-down” isomers (b) at room temperature indicate that the two S-C₆F₅ ligands in the 2-up equatorial positions have restricted rotation about their C–S bonds, but this rotation becomes free as the temperature increases. Room temperature ¹⁹F NMR spectra of 3 and 5 also indicate restricted rotation around the Os–P bonds in the “2-up, 1-down” isomers (b). In addition, as the temperature increases, the ¹⁹F NMR spectra tend to be consistent with an increased rate of the isomeric exchange. Variable temperature ³¹P{¹H} NMR studies also confirm that, as the temperature is increased, the a and b isomeric exchange becomes fast on the NMR time scale.     

Synthesis of 5-substituted-3-phenacyloxime-1,2,4-oxadiazoles from acetylated or benzoylated benzoylthiacetamide with hydroxylamine hydrochloride : Spectral evidence for a tetrahedral carbinolamine intermediate

Acetylated and benzoylated benzoylthiacetamide 1a,b reacts with hydroxylamine hydrochloride in refluxing ethanol to yield 3 - acetylamino - and 3 - benzoylamino - 5 - phenyl - isoxazoles 2a,b, while 3 -phenacyloxime - 5 - substituted - 1, 4a,b are formed in the presence of sodium acetate or in pyridine.When refluxed in ethanol containing small amounts of concentrated hydrochloric acid, the above 1,2,4-oxadiazoles 4a, b rearrange to the corresponding isoxazoles 2a, b.The reaction in pyridine has been studied at 35° by using ¹H and ¹³C NMR spectroscopy. It has been possible to detect an adduct between the carbinolamine intermediate, resulting from the addition of hydroxylamine to the keto carbonyl group, and the starting thiamide.     

Investigation on the chemistry of berbans—VIII : Synthesis of “inside” depyrrolo-yohimbine analogues

Previously known ketonitrile 1 with phosponic acid ester 2 produced the two geometrical isomers 3 and 4 which upon reduction afforded 5b and 6b. By hydrolysis and subsequent esterification the two methyl esters 5a and 6a were obtained. Dieckmann condensation of 5a led to 7a and 7b. Reduction of the latter compounds yielded the corresponding “inside” yohimbine analogues 8a and 8b. Methyl ester 6a was converted into the ketoester 9. The stereochemistry of the isomers was proved by physical (H¹ NMR, IR, MS) and by chemical methods.     

9(11)-Secoestra-11,17-dioic acids and related compounds

While hydrogenations of 2b furnished a mixture in which the rac 14α isomer 8b predominated, the rac lactone 6 was hydrogenolyzed to give the rac 14β diacid 9a. Clemmensen reduction of 6 gave the rac 14α tetrahydro compound 7a. Another route to 8 involved conversion of the d-ketoacid 11b into 23b via the cyanolactone 20b or the amidolactone 21b. Base-catalyzed elimination at 206° yielded the Δ¹⁶ diester 27 which was hydrogenated to 8c. An analogous conversion was also carried out in the ring B reduced series 13 → 20a + 21a → 23a → 25a → 26. In the 14β series, using the same sequence of reactions, the rac ketoacid 10a was transformed into the rac lactone ester 29. In distinction from the 14α series, treatment with alkali at 206° gave only partial elimination, the double bond migrating to the 14,15 position to furnish 2. Evidence is presented that amides of the ketoacid 13a exist in the hydroxylactam form 30 and can be readily O-alkylated to furnish 22. Attempts to aromatize ring B of 13a with DDQ led to lactones 15 and 16, while reaction of the ester 13b with DDQ gave the pentaene 17 and the hexaene 18, establishing that dehydrogenation proceeded stepwise in the sequence Δ⁸, Δ¹⁴ and finally Δ⁶.     

Preparation of (1R,8S)- and (1S,8R)-9-azabicyclo[6.2.0]dec-4-en-10-one: potential starting compounds for the synthesis of anatoxin-a

9-Azabicyclo[6.2.0]dec-4-en-10-one (±)-2, obtained from cyclooctadiene by addition of chlorosulfonyl isocyanate, was N-hydroxymethylated to (±)-3 and then resolved by lipase-catalysed asymmetric acylation of the primary OH group at the (S)-stereogenic centre. High enantioselectivity (E=94) was observed when lipase PS and vinyl butyrate were used in di-iso-propyl ether at −15°C, resulting in the enantiomerically enriched ester 3a and alcohol 3b (e.e. ≥92%). Treatment of 3a and 3b with NH₄OH/MeOH afforded the corresponding β-lactams (1R,8S)-2a and (1S,8R)-2b (e.e. ≥93%), potential starting compounds in anatoxin-a synthesis. The ring opening of lactams (±)-2, (±)-7, 3a and 3b, followed by reduction, resulted in racemic 4–6 and 8 and enantiomeric 4a, 4b, 5a and 5b eight-membered cyclic β-amino acid derivatives.     

Synthesis and characterization of new (pyrazolyl)aryl phosphinite PCN pincer palladium(II) complexes

Two unsymmetrical PCN pincer Pd(II) complexes 3a–3b which are based on (pyrazolyl)aryl phosphinite ligands and contain two fused six-membered palladacycles have been synthesized from 3-(3,5-dimethylpyrazol-1-ylmethyl)benzyl alcohol (2) by one-pot phosphorylation/palladation reaction via C–H bond activation of the related ligands. The pyrazole-coordinated phosphine-free Pd(II) complex (4) was also isolated in the preparation of pincer complex 3a. The new complexes were characterized by elemental analysis, ¹H NMR, ¹³C NMR, ³¹P {¹H} NMR (for pincer complexes) and IR spectra. And the molecular structures of 3b and 4 have been further determined by X-ray single-crystal diffraction. The pincer Pd complexes 3a and 3b exhibited rather low activity in the allylation of benzaldehyde.     

Reactivity of 1-boraadamantanes towards bis(trialkylstannyl)ethynes. First examples of 3-boratricyclo[5.3.1.1]dodecanes, and the molecular structure of a tetraalkyldiboroxane

1-Boraadamantane (1) and 2-ethyl-1-boraadamantane (1(2-Et)) react with bis(trialkylstannyl)ethynes (3), R₃Sn-CC-SnR₃ with R=Me (a), Et (b), in a 1:1 molar ratio by 1,1-organoboration under very mild conditions to give the 4-methylene-3-borahomoadamantane derivatives 4a,b and 7a,b, respectively, which are dynamic at room temperature with respect to deorganoboration. The compounds 4a,b react further with 3a,b by 1,1-organoboration to the tricyclic butadiene derivatives 5a,b. Attempts to crystallise 4a afforded the product of hydrolysis, the diboroxane 6a which was characterised by X-ray structural analysis. All products were characterised in solution by ¹H-, ¹¹B-, ¹³C- and ¹¹⁹Sn-NMR spectroscopy.     

Enamine chemistry-XXVI: The [4 + 2] cycloaddition reactions of 3-amino-1-(4-nitrophenyl)-prop-2-ene-1-thione with electrophilic olefins and acetylenes

Enamino-thiones 1 prepared from the corresponding enaminones by thiation with Lawesson's Reagent, were allowed to react with 2-chloroacrylonitrile and dimethyl acetylenedicarboxylate giving dihydro-2$\text{H}$-thiopyrans, 2, and 4$\text{H}$-thipyrans, 3, respectively. The reaction of 1a with ethyl propiolate at room temperature afforded 4$\text{H}$-thipyrans, 4a, which on standing rearranged to 2$\text{H}$-thiopyran, 5a(1, 3 amide shift). The reaction of 1b with ethyl propiolate produced 4b and 5b. Some of the ¹³C NMR data are reported.     

A synthesis of (±)-Δ2-α-Lycoren-7-one,the key intermediate for the total synthesis of (±)-lycorine

(±)-α-Lycoran-3,5-dione (14a) was prepared from octahydrophenanthridin-3-one (8b) obtained by two methods starting from 5-aryl-4-nitrocyclohexene (2) and 1-hydroxyl-2-aryl-5-oxo-cyclohexanecarboxylic acid (10), both of which were prepared by the Diels-Alder reaction of 3,4-methylenedioxy - ω - nitrostyrene with butadiene and the Robinson annelation of 3,4-methyl- enedioxy - phenylpyruvic acid (9) with methyl vinyl ketone, respectively, 14a was converted into (±)Δ²-α-lycoren-7-one (22b), which has been transformed into (±)-lycorine (1) by Torssell     

Masked constrained cysteines: diastereoselective and enantioselective synthesis of 1-amino-2-mercaptocyclopropanecarboxylic acid derivatives

A diastereoselective and enantioselective synthesis of (Z)-1-benzoylamino-2-tritylsulfanylcyclopropanecarboxylic acid derivatives 8a,b and 9a,b was achieved starting from (−)- or (+)-menthyl 2-benzoylamino-3-tritylsulfanylacrylates 3a,b. Compounds 3 were reacted with diazomethane giving the corresponding pyrazolines 4a,b and 5a,b. These compounds, on melting, were transformed, under steric control, into the cyclopropaneamino acid derivatives (R,R)-8a,b and (S,S)-9a,b. The synthesis of a large class of chiral 2-S-alkyl-1-aminocyclopropanecarboxylic acid derivatives is possible after removing the trityl protecting group and subsequent alkylation reactions.     

Über die Synthese von 1,3-Dihydro-3-(2-dimethylaminoäthyl)-1-(3-thienyl)-benzimidazol-2-onen

The synthesis of 1-(3-thienyl)-benzimidazol-2-ones (3 a and4), described in an earlier paper¹, has been further investigated. The Na-salt of3 a is converted to a benzimidazolone substituted in position 3 (3 b). Dehydrogenation of the thiophene nucleus of3 a with chloranil yields5 a, which undergoes substitution in position 3 with Cl(CH₂)₂N(CH₃)₂ to give5 b. Monochlorination of5 a yields5 c, the structure of which is confirmed by¹H-NMR-spectroscopy.5 d is obtained by reaction of the Na-salt of5 c with Cl(CH₂)₂N(CH₃)₂.      

Solvent-dependent reactivities of acyclic nitrones with β-diketones: catalyst-free syntheses of endiones and enones

Reactions of the nitrones ^?O⁺N(Me)C(H)Ar 1 (Ar=phenyl 1a, 4-methylphenyl 1b, 2,4,6-trimethylphenyl 1c, and anthracen-9-yl 1d) with the cyclic β-diketones 1,3-indandione 2 or barbituric acid 3 in CH₂Cl₂, afford the corresponding endiones 2′a–2′d or 3′a–3′d. In contrast, dimedone 4 reacts with 1a or 1b to give the endione 4′a or 4′b and the bis-adduct 4″a or 4″b. Nevertheless, reaction of 4 with 1c or 1d in CH₂Cl₂ furnishes only the endione adducts 4′c or 4′d. However, the reaction of 4 with 1a or 1b in methanol gives only 4″a or 4″b, respectively. Among acyclic β-diketones only malonic acid 7 reacts with 1a–1c. Reaction of 7 with 1a in CH₂Cl₂ forms cinnamic acid 7″a, whereas in the case of 1b, the endione 7′b and (E)-3-p-tolylacrylic acid 7″b are obtained. The nitrone 1c reacts with 7 in CH₂Cl₂ to afford the endione 7′c or with acetone yielding (E)-4-mesitylbut-3-en-2-one 8. X-ray analyses are reported for 4′c, 5, and 7″b. In addition, the calculated acidity of the hydrogen at the α-C atom is shown to correlate with the reactivity of the β-diketones with nitrones.     

Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

N-mesityl-N′-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N′-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl₃ · xH₂O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ²-2)₂Ru(μ-Cl)₂Ru(κ²-2)₂]²⁺ [3a]²⁺. The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-μ-bromo bridged derivative [(κ²-2)₂Ru(μ-Br)₂Ru(κ²-2)₂]²⁺ [3b]²⁺ was obtained from RuCl₃ · xH₂O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]²⁺ reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]⁺. Reaction of [3a]²⁺ with the sodium salt of l-proline resulted in a diastereomeric mixture of complexes [5]⁺. The free N-heterocyclic carbene 2 reacts with [FeCl₂(PPh₃)₂] to give after anion exchange with NaBPh₄ cis/cis/trans coordinated [Fe(κ²-2)₂(MeCN)₂](BPh₄)₂ [6](BPh₄)₂. The molecular structures of [3b](PF₆)₂, [4]PF₆ and [6](BPh₄)₂ · H₂O are reported.     

Phosphorus-nitrogen compounds part 22. Syntheses, structural investigations, biological activities and DNA interactions of new mono and bis (4-fluorobenzyl) spirocyclophosphazenes

The reactions of hexachlorocyclotriphosphazene, N₃P₃Cl₆, with mono (1 and 2) and bis(4-fluorobenzyl) diamines (3-5), FPhCH₂NH(CH₂)_nNHR (RH or FPhCH₂-), produce mono (1a and 2a) and bis(4-fluorobenzyl) monospirocyclophosphazenes (3a-5a). The tetraaminomonospirocyclophosphazenes (1b-2d) are obtained from the reactions of the partly substituted phosphazenes (1a and 2a) with excess pyrrolidine, morpholine and 1,4-dioxa-8-azaspiro[4,5]decane (DASD), respectively. The tetrachlorobis(4-fluorobenzyl) monospirocyclophosphazenes (4a and 5a) with excess pyrrolidine, morpholine and DASD afford the fully substituted bis(4-fluorobenzyl) monospirocyclophosphazenes (4b, 4d-5d) in boiling THF. In addition, monochlorobis(4-fluorobenzyl) monospirocyclophosphazenes (4e and 4f) have also been isolated from the reactions with excess morpholine and DASD in boiling THF. The structural investigations of the compounds have been verified by elemental analyses, MS, FTIR, ¹H, ¹³C, ¹⁹F (for 1d and 2d), ³¹P NMR, HSQC and HMBC techniques. The crystal structures of 3a, 4a, 5a and 2b have been determined by X-ray crystallography. The compounds 2a-5a, 1b-2d, 4b, 4d-5d, 4e and 4f have been screened for antibacterial effects on bacteria and for antifungal activity against yeast strains. The compounds 1b and 4b showed antimicrobial activity against three species of bacteria, Bacillus subtilis, Bacillus cereus and Staphylococcus aureus, and two fungi, Candida albicans and Candida tropicalis. Minimum inhibitory concentrations (MIC) were determined for 1b and 4b. The MIC values were found to be 5000 μM for each bacteria. The most effective compound, 4b has exhibited activity with a MIC of 312 μM for C. albicans and 625 μM for C. tropicalis. DNA-binding and the nature of the interaction with pBR322 plasmid DNA are studied. All of the compounds induce changes on the DNA mobility and intensity. Prevention of HindIII digestion with the compounds indicates that the compounds bind with AT nucleotides in DNA.     

Reduction of cephalosporanic acids with chromium(II) salts : Synthesis of 3-methylenecepham derivatives

7-Acylaminocephalosporanic acid derivatives (1) were converted into 7-acylamino-3-methylenecepham-4-carboxylic acids (2) by treatment with chromium(II) salts in aqueous media. The esters (4a or 4b) of 7-acylamino-3-methylenecepham compounds were readily isomerized to the 3-methyl-3-cephem compounds (5a or 5b) under basic conditions. The reaction mechanism is discussed.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Rearrangement of the carbon skeleton in the intramolecular photoadduct of anthracene and benzene rings

The effectivity of optical switching between anthracene derivatives 3a,b and their intramolecular photocycloadducts 4a,b is impaired by traces of acid. The systematic treatment of 4a,b with an increasing excess of formic acid revealed that—apart from the normal enolether cleavage 4a,b→6a,b→7a,b—a cleavage with rearrangement of the carbon skeleton can occur: 5b→6b′. The driving force is a stability enhancement of the involved carbenium ions 5b→5b′. A further increased excess of formic acid leads finally to a competitive ether cleavage in the tetrahydrofuran ring 5b→8.