Säurekatalysierte Dienon-Phenol-Umlagerungen von 6-Propargyl-6-methyl-cyclohexa-2,4-dien-1-onen; ladungskontrollierte,aromatische [1s, 2s]- und [3s, 4s]-sigmatropische Reaktionen

The acid catalysed dienone-phenol rearrangement of methyl substituted o-propargyl-cyclohexadienones (scheme 3) was investigated. The rearrangements were carried out in acetic anhydride containing about 1⁰/₀₀ sulfuric acid. Under these conditions acetoxy benzenium ions are formed as intermediates. These then undergo charge-controlled [3s, 4s]- and [1s, 2s]-sigmatropic rearrangements. Thus, the [3s, 4s]-process leads to the formation of the corresponding allenyl-phenol acetates ( 19 , 21 , 23 , 25 , 28 , 30 ) whereas the [1s, 2s]-process yields propargyl-phenol acetates ( 20 , 22 , 24 , 26 , 29 ), respectively (cf. scheme 4).     

Palladium(0)-Catalyzed Cyclizations of Simple 1-Aryl-1,7-octadien-3-yl Acetates. Preliminary communication

Dienyl acetates 2 lacking a geminal disulfone or a malonate group cyclize selectively to (E)-l-methylidene-2-styrylcyclopentanes 4 in the presence of 7 mol-% of [Pd(PPh₃)₄].     

CuSO<Subscript>4</Subscript> as a Mild,Green, and Efficient Catalyst for the One-pot Conversion of <Emphasis Type="Italic">THP</Emphasis> Ethers to Acetates

Summary. An efficient direct conversion of THP ethers into the corresponding acetates was achieved with acetic anhydride in the presence of CuSO₄ · 5H₂O as an available and green catalyst in high yields.     

Preparation and characterization of superconducting YBa<Subscript>2</Subscript>(Cu<Subscript>1−x</Subscript>Cr<Subscript>x</Subscript>)<Subscript>4</Subscript>O<Subscript>8</Subscript> oxides by thermal analysis

In this study the formation of chromium substituted YBa₂Cu₄O₈ (Y-124) superconductors has been investigated by TG/DTA measurements. The YBa₂(Cu_1−xCr_x)₄O₈ ceramics with nominal compositions of x=0.01, 0.03, 0.05, 0.10 and 0.20 have been prepared by an aqueous sol-gel method using aqueous mixtures of the corresponding metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. To assist the interpretation of the results obtained the synthesis products were additionally characterized by X-ray powder diffraction (XRD) and resistivity measurements. It was determined that doping the YBa₂Cu₄O₈ phase with chromium has a strong effect on the phase purity and superconducting properties of the synthesis products.     

Synthesis of 2,3‐Diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐ol Derivatives by the Reaction of Aryl(3‐isocyanopyridin‐4‐yl)methanones with Aryl Grignard Reagents

The reaction of aryl(3‐isocyanopyridin‐4‐yl)methanones 1 , easily prepared from commercially available pyridin‐3‐amine, with aryl Grignard reagents gave, after aqueous workup, 2,3‐diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐ols 2 . These rather unstable alcohols were O‐acylated with Ac₂O in pyridine in the presence of a catalytic amount of 4‐(dimethylamino)pyridine (DMAP) to afford the corresponding 2,3‐diaryl‐3H‐pyrrolo[2,3‐c]pyridin‐3‐yl acetates 3 in relatively good yields.     

A Simple Multistep Conversion of 1,2‐Dihydro‐1,1‐dimethoxynaphthalen‐2‐ones to (3,4‐Dihydro‐3,4‐dioxonaphthalen‐2‐yl)acetates

On irradiation (λ=350 nm) in the presence of 1,1‐dimethoxyethene, naphthalene‐1,2‐dionemonoacetals 1 regioselectively afford 1,1,4,4‐tetramethoxycyclobuta[a]naphthalen‐3‐ones 3 . Sequential deprotection of these bis‐acetals first lead to 1,1‐dimethoxycyclobuta[a]naphthalene‐3,4‐diones 4 and then to cyclobuta[a]naphthalene‐1,3,4‐triones 6 , which, in turn, are converted into (3,4‐dihydro‐3,4‐dioxonaphthalen‐2‐yl)acetates 7 by treatment with SiO₂/MeOH/air.     

Synthesis of (4Z)‐4‐(Arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones by the Reaction of Ethyl (2Z)‐3‐Aryl‐2‐isothiocyanatoprop‐2‐enoates with Organolithium Compounds

A convenient one‐pot method for the preparation of (4Z)‐4‐(arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones 2 and 3 from ethyl (2Z)‐3‐aryl‐2‐isothiocyanatoprop‐2‐enoates 1 , which can be easily prepared from ethyl 2‐azidoacetate and aromatic aldehydes, has been developed. Thus, these α‐isothiocyanato α,β‐unsaturated esters were treated with organolithium compounds, including lithium enolates of acetates, to provide 5‐substituted (4Z)‐4‐(arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones, 2 , and 2‐[(4Z)‐(4‐arylmethylidene)‐5‐ethoxy‐2‐thioxo‐1,3‐oxazolidin‐5‐yl]acetates, 3 .     

Synthesis of Pyrrolo[2,1-<Emphasis Type="Italic">b</Emphasis>]thiazol-3-one Derivatives

Summary. Ethyl [4-oxo-3-(2-oxo-2-arylethyl)thiazolidin-2-ylidene]acetates and [4-oxo-3-(2-oxo-2-arylethyl)thiazolidin-2-ylidene]acetonitriles were shown to react with substituted benzaldehydes at the endocyclic methylene group leading to the corresponding 5-arylmethylidene derivatives. Their treatment with DMF · POCl₃ complex yielded 3-oxo-5-aroyl-2-arylmethylidene-2,3-dihydropyrrolo[2,1-b]thiazole-7-carboxylic acids ethyl esters and -7-carbonitriles. The structures of the pyrrolothiazoles were confirmed by an X-ray crystallographic study, which indicated the (Z)-configuration at the arylmethylidene moiety.     

Asymmetric and ‘anti’-Selective Aldolisations of Acetates and Propionates. Preliminary Communication

Starting from acetates 1 and propionates 6 , TiCl₄-mediated addition of their silyketene acetals 2 and 7 to aldehydes gave aldols 4 and 9 , respectively, with high π-face and ‘anti’ differentiation (Schemes, and Tables 1 and 2). Alternation of the (E/Z)-enolate geometry led to reversed α- and β-inductions ( 7 → 9b , 8 → 10b ). Non-destructive removal of the auxiliary yielded enantiomerically pure β -hydroxycarboxylic acids 13 .     

Unimolecular and collision-induced dissociation reactions of peracetylated methyl glucopyranoside

The mechanism of the collision-induced fragmentation of peracetylated methyl-α-D-glucopyranoside was investigated using deuterium-labelled acetates and sequential mass spectrometry. Loss of the substituent at C(1), the anomeric carbon, yields an ion of m/z 331, [C₁₄H₁₉O₉]⁺. This ion further dissociates via two pathways, the first including m/z 271, [C₁₂H₁₅O₇]⁺, 169, [C₈H₉O₄]⁺ and 109, [C₆H₅O₂]⁺, and the second including m/z 211, [C₁₀H₁₁O₅]⁺, 169, [C₈H₉O₄]⁺ and 127 [C₆H₇O₃]⁺. The first path proceeds via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(2)-acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an ill-defined series of parallel decomposition reactions involving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4).     

Stereoselektive Totalsynthese von natürlichem Phytol und Phytolderivaten und deren Verwendung zur Herstellung von natürlichem Vitamin K1

Steroselective Total Synthesis of Natural Phytol and Derivatives thereof; Use of these Compounds in the Synthesis of Natural Vitamin K₁ The Li₂CuCl₄-catalyzed couplings of the easily accessible bifunctional C₅ allylic acetates (E)- 18a and (E)- 18b with racemic hexahydrofarnesylmagnesium bromide ((3 RS/RS, 7 RS/SR)- 19a ) proceed with high chemo- and stereoselectivity (≥98% (E)-retention) to give the (2E, 7 RS/RS, 11 RS/SR)-phytol derivatives 1a and 1b , respectively, in yields of 72–80% (Scheme 5). The same couplings performed with optically active hexahydrofarnesylmagnesium bromide (3 R, 7 R)- 19a yielded the (E)-phytol derivatives of the natural series (7 R, 11R)- 1a and (7 R, 11 R)- 1b. Acid-catalyzed hydrolysis of(2 E, 7 R, 11 R)- 1b gave natural phytol((2 E, 7 R, 11 R)- 1c ) Friedel-Crafts alkylation of ‘menadiol monobenzoate’ 11b with (2 E, 7 R, 11 R)- 1a or (2 E, 7 R, 11 R)- 1b gave the dihydrovitamine K₁ derivative (2 E/Z, 7′ R, 11′R)- 12b ((E/Z)≈? 9:l). Conversion of configurationally pure (2 E, 7′ R, 11′ R)- 12b (yield 73%; obtained after chromatographic removal of the (Z)-isomer) into natural vitamine K₁ ((2 E,7′ R, 11′ R)- 2 ) was achieved in the usual way by saponification and oxidation with air. Some further investigations of the coupling reactions of bifunctional C₅ allylic synthons with hexahydrofarnesylmagnesium bromide (3 RS/RS, 7 RS/SR)- 19a showed the outcome of these reactions to be critically dependent on the nature of the leaving group, the double-bond geometry and the nature and concentration of the catalyst. Thus, the Li₂CuCl₄-catalyzed couplings of (3 RS/RS,7 RS/SR)- 19a with the allylic halides 29a and 29c as well as with p-toluenesulfonate 29b yielded besides the phytol derivatives 1a and 1b - also the S_N2′-type products 30a and 30b (Scheme 8, Table 2); the same result was found for the coupling with the cis-configurated allylic acetates (Z)- 18a and (Z)- 18b (Table 3). A similar loss of chemo selectivity as well as the loss of stereoselectivity in the coupling reactions of 19 with the bifunctional (E)-olefins of type 18 was observed when the Li₂CuCl₄-catalyst concentration was increased from 0.2 to 25 mol-% or upon substitution of Li₂CuCl₄ by copper (I) chloride or iodide (Table 4).     

Chiral Acylsilanes in Organic Synthesis. Part 3. Silicon-directed stereoselective preparation and Ireland ester-enolate rearrangement of O-acyl-substituted α-silylated allyl alcohols

Stereocontrolled addition of alk-1-enylmetal reagents to the chiral (alkoxymethyl)-substituted acylsilanes (±)- 6 gave rise to α-silylated allyl alcohols, which were converted to the corresponding acetates or propionates 11–16 (Scheme 2). Deprotonation and silylation with Me₃SiCl afforded – in an Ireland ester-enolate-accelerated Claisen rearrangement – stereoselectively αδ-silylated γδ-unsaturated carboxylic acids 18–24 (Scheme 4). The Me₃Si groups in α-position to the COOH group of these compounds were removed chemoselectively in presence of the chiral silyl group in δ-position by treatment with Bu₄NF · 3 H₂O or Et₃N · 3 HF (→ 27–32 ; Scheme 5). The reaction sequence allows a novel stereocontrolled access to chiral C-frameworks possessing a vinylsilane moiety with its full reaction potential.     

Synthese von Benzofulvenen und Dibenzofulvenen über 1-Chloralkyl-acetate

Synthesis of benzofulvenes and dibenzofulvenes via 1-chloroalkyl-acetates 1,2-Benzofulvene (6a) and 1,2,3,4-dibenzofulvene (7a) as well as the corresponding 6-methyl- and 6-phenyl-derivatives are prepared by reaction of sodium indenide and sodium fluorenide with 1-chloroalkyl acetates (3) , followed by elimination with KOC(CH₃)₃. The over-all yields are comparable with the results of the fulvene series and are in most cases considerably higher than the yields of the Thiele-method.     

Syntheses and crystal structures of two complexes based on 2-amino-4,6-bis(4-pyridyl)-1,3,5-triazine

Two compounds based on 2-amino-4,6-bis(4-pyridyl)-1,3,5-triazine (4-HABPT), [Co(4-HABPT)₂(H₂O)₄](CH₃COO)₂ (1), and Zn(4-HABPT)₂Cl₂ (2) were obtained at room temperature. Single-crystal X-ray diffraction analyses indicate that 1 crystallizes in the triclinic P 1 with cobalt(II) coordinated by two 4-HABPT and four waters, two acetates are counter ions. The complex cations and acetates are linked to a 3-D framework by hydrogen bonds. Compound 2 crystallizes in the orthorhombic Pnc2 with zinc(II) coordinated by two 4-HABPT and two chlorides in a tetrahedral geometry; the complex also forms a 3-D framework by hydrogen bonds and π?···?π interactions.     

One‐Pot Syntheses of 2‐(2‐Sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic Acid Derivatives via Reactions of 3‐(2‐Isothiocyanatophenyl)prop‐2‐enoic Acid Derivatives with Thiols or Sodium Sulfide

Two efficient methods for the preparation of 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 3 under mild conditions have been developed. The first method is based on the reaction of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoates 1a – 1c with thiols in the presence of Et₃N in THF at room temperature, leading to the corresponding dithiocarbamate intermediates 2 , which underwent spontaneous cyclization at the same temperature by an attack of the S‐atom at the prop‐2‐enoyl moiety in a 1,4‐addition manner (Michael addition) to give 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetates in one pot. The second method involves treatment of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoic acid derivatives 1b – 1d with Na₂S leading to the formation of 2‐(2‐sodiosulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid intermediates 5 by a similar addition/cyclization sequence, which are then allowed to react with alkyl or aryl halides to afford derivatives 3 . 2‐(2‐Thioxo‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 6 can be obtained by omitting the addition of halides.     

An Efficient Friedel–Crafts/Oxa‐Michael/Aromatic Annulation: Rapid Access to Substituted Naphtho[2,1‐b]furan,Naphtho[1,2‐b]furan,and Benzofuran Derivatives

Substituted naphthofurans and benzofurans are easily accessible by treatment of naphthols/substituted phenols with nitroallylic acetates through a substitution–elimination process promoted by cesium carbonate. Reactions between naphthols and aromatic/heteroaromatic‐substituted nitroallylic acetates gave the desired functionalized naphthofurans in high to excellent chemical yields (14–97 %). On the other hand, treatment of phenol derivatives (i.e., 3‐dimethylamino‐, 3‐methoxy‐, and 3,5‐dimethoxyphenol) with various nitroallylic acetates afforded the corresponding benzofurans in moderate to good chemical yields (24–91 %). The reaction proceeded through an interesting Friedel–Crafts S_N2′ process followed by intramolecular oxa‐Michael cyclization and subsequent aromatization. A plot of log (k/k_H) against Hammett constants σ_p showed satisfactory linearity with a positive ρ value, indicating that the initial Friedel–Crafts‐type S_N2′ process constituted the rate‐determining step. This methodology has been applied to the synthesis of various novel C₂ and C₃ symmetric bis‐ and trisfurans by using catechol and phloroglucinol as the nucleophilic partners. The reactivity decreased when alkyl‐substituted nitroallylic acetate systems were used. This might be related to the decreased electrophilic character of these substrates.     

Cationic polymerization of styrenes by activated covalent species. Direct 1H-NMR observation of complexes of 1-phenylethyl acetates with lewis acids

Complexes of boron trichloride, boron tribromide, and ethylaluminumdichloride with various acetates were directly observed by ¹H-NMR. Complexes of secondary and tertiary acetates which model macromolecular active species in polymerization of styrene and isobutene are stable at ?75°C, but decompose at temperatures above ?30°C to yield corresponding chlorides or bromides. The stability of complexes depends on the Lewis acid, the alkyl group in the ester, and the structure of acetate. Rates of the bimolecular exchange of complexes with excess acetate were calculated from dynamic NMR to be k_ex = 2 × 10¹ L mol^?1 s^?1 (?65°C) and k_ex = 5 × 10⁴ L mol^?1 s^?1 (?75°C) for 1-phenylethyl acetate with BCl₃ and EtAlCl₂, respectively.     

New polymer syntheses 22. LC-poly(esterimide)s derived from trimellitic acid, ω-amino acids and hydroquinone or 4,4′-dihydroxybiphenyl

Diacids with variable spacer length were prepared by condensation of trimellitic anhydride and ω-amino acids. From these diacids, homopolyesters were prepared by thermal condensation with the acetates of hydroquinone or 4,4′-dihydroxy biphenyl and a series of copolyesters containing 4-hydroxy benzoic acid. The same LC poly(ester imide)s could also be prepared in a “one-pot procedure” from trimellitic anhydrid, lactams, and bisphenol acetates. The differential scanning calorimetry (DSC) traces of most poly(ester imide)s exhibit two endotherms representing the solid → LC phase transition (Tm₁) and the LC phase → isotropic melt transition (Tm₂). Observation under the polarizing microscope and wide-angle X-ray scattering (WAXS) measurements suggest that the LC phase formed immediately above the melting points (Tm₁) have a smectic character. Poly(ester imide)s of 4,4′-dihydroxybiphenyl possess higher melting points and a broader temperature range of the LC phase than those of hydroquinone. The copolyesters possess a nematic melt over a broad temperature range. Thermomechanical analyses under low pressure (0.05 kg/mm²) gave heat distortion temperatures close to the melting points (Tm₁), and under high pressure (1 kg/mm²), values between Tm₁ and the glass transition temperatures (T_g). Thermogravimetric measurements indicate that processing from the melt is feasible up to temperatures around 340°C.     

Ion–molecule reactions in the gas phase. XVIII.—nucleophilic substitution of diastereomeric norborneols,norbornyl acetates and benzoates under ammonia chemical ionization

The comparative behaviour of the endo- and exo-norborneols and diastereomeric derivatives (acetates and benzoates) towards the NH₃/NH₄⁺ system was investigated. It appears that the proton affinity (PA) of the substrate relative to Pa(NH₃) strongly influences competition between the protonation and nucleophilic substitution processes yielding the MH⁺ and [M + NH₄ ? H₂O]⁺ ions, respectively. Tandem mass spectrometry was used to compare collision-activated dissociation spectra of [M + NH₄ ? H₂O]⁺ with those of analogous endo- and exo-norbornylamines protonated in the source. This demonstrates that an S_Nimechanism occurs specifically for the isomeric norborneols; in contrast, for acetates and benzoates, stereospecific S_Ni and S_N2 pathways take place for exo and endo derivatives, respectively. This particular behaviour is explained by considering the steric effect induced by the endo-H at C(6). In addition, the competitive decompositions of [M + NH₄ – H₂O]⁺ into NH₄⁺ and [C₇H₁₁]⁺ daughter ions are consistent with the formation of a proton-bound complex intermediate. The observed stereochemical effects for these dauther ions are rationalized by means of arguments based on the estimated heats of formation of the transition states, which is lower for the exo-norbonyl protonated amine, consistent with anchimeric assistance, rather than a stepwise pathway which is proposed for the endoisomer.     

Complex Compounds of Azomethines with an MN2S2 Five-membered Coordination Unit: Metal Chelates of 2-{[4-(3,5-Diphenyl-4,5-dihydropyrazol-1-yl)benzylidene]amino}benzenethiol

Chelate complexes of 2-{[4-(3,5-diphenyl-4,5-dihydropyrazol-1-yl)benzylidene]amino}benzenethiol (LH) of the ML₂ composition and with an M₂N₂S₂ five-membered coordination unit were obtained. The syntheses were carried out by chemical (from LH and metal acetates) and electrochemical (from LH and zerovalent metals) methods in methanol. The chelate compounds were assigned cis-planar (M = Ni) and tetrahedral (M = Co, Zn, Cd) configurations.