Lattice modes of polyethylene

Summary The lattice modes of polyethylene with the phase differences ( and along the-axis and theb-axis were calculated at intervals of 30 for the phase differences. They wereT _x, T_y, T_x, T_y, R_z andR _z, and some special conditions of the phase differences separated the six modes. To know the reliability of the intermolecular force constants used in this calculation, the elastic moduli of polyethylene crystal along thea-axis and theb-axis were calculated with the modified potential functions and compared with the observed values.

---

Zusammenfassung Die Gitterschwingungen in PolyÄthylen mit den Phasendifferenzen und lÄngs dera- undb-Achsen wurden in Intervallen von 30 der Phasendifferenzen berechnet. Das gibt 6 Hauptschwingungen,T _x, T_y, T_x,T _y, R_z und R_z. Um die ZuverlÄssigkeit der intermolekularen Kraftkonstanten, die bei diesen Berechnungen verwendet wurden, zu prüfen, wurden die elastischen Moduln von PolyÄthylen-Kristallen in Richtung dera- undb-Achse unter bestimmten modifizierten PotentialverlÄufen berechnet und mit den beobachteten Werten verglichen.

     

Palladium(II) and platinum(II) chloride and bromide complexes with some 2-methylpyridyl- or methylquinolyl-benzimidazole,benzoxazole, or benzthiazole

Summary Palladium(II) and platinum(II) complexes [MLX₂], where L=2-(4-methyl-2-pyridyl)benzimidazole (mpbi), 2-(4-methyl-2-pyridyl)benzoxazole (mpbo), 2-(4-methyl-2-quinolyl)benzoxazole (mpbo), 2-(4-methyl-8-quinolyl)benzoxazole (mq'bo), X=Cl. Br, together with M(mqbo)₂Br₂ and Pt₂(mpbt)Cl₄, where mpbt=2-(4-methyl-2-pyridyl)benzthiazole, have been synthesized and characterized by conductivity and magnetic measurements as well as by i.r. and electronic spectra. The ligands are bidentate chelates through the pyridine or quinoline and isoxazole or imidazole nitrogen atoms. The [MLX₂] derivatives arecis, square planar.     

Synthesis of some 5′-O-amino acid derivatives of uridine as potential inhibitors ofUDP-glucuronosyltransferase

Summary In an attempt to develop potential inhibitors ofUDP-glucuronosyltransferase, some 5-O-amino acid derivatives of uridine were synthesized. N-protectedL-amino acids were coupled at the 5-O-position of 2,3-O-isopropylideneuridine by esterification employing the method of symmetrical anhydrides in presence of 4-dimethylaminopyridine, 5-O-(N-benzyloxycarbonyl-O-tert.butyl-L-threonl)-23-O-isopropylideneuridine (1), 5-O-(N-tert.butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylideneuridine and (2), 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (3), and 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (4) were obtained in good yield after column chromatography on silica gel. The treatment of2 withTFA/CH₂Cl₂ (6:1) at room temperature for 30 min led to a selective removal of theBoc group without deblocking of the 2,3-O-isopropylidene group of uridine. Treatment of2 withTFA/H₂O (5:1) at room temperature for 1 h, however, released bothBoc and 2,3-isopropylidene groups. TheZ group of1 was deprotected by catalytic hydrogenolysis over 10% Pd/C/ammonium formate.

---

Synthese von 5-O-Aminosäurederivaten des Uridins als potentielle Inhibitoren derUDP-Glukuronosyl-Transferase

Zusammenfassung In einem Versuch, potentielle Inhibitoren derUDP-Glukuronosyl-Transferase zu entwickeln, wurden einige 5-O-Aminosäurederivate des Uridins synthetisiert. N-GeschützteL-Aminosäuren wurden durch Veresterung mit der 5-O-Position des 2,3-isopropylidenuridins gekuppelt (Methode der symmetrischen Anhydride in der Gegenwart von 5-Dimethylaminopyridin). Solcherweise wurden 5-O-(N-Benzyloxycarbonyl-O-tert.butyl-L-threonly)-2,3-O-isopropylidenuridin (1), 5-O-(N-tert.Butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylidenuridin (2), 5-O-(N-tert.Butyloxycarbonyl-L-leucyl)-2,3-O-isopropylidenuridin (3) und 5-O-(N-tert.Butyloxycarbonyl-L-valyl)-2,3-O-isopropylidenuridine (4) nach Säulenchromatographie (Kieselgel) in guter Ausbeute hergestellt. Die Behandlung von2 mitTFA/CH₂Cl₂ (6:1) bei Zimmertemperatur (30 min) führte zu einer selektiven Abspaltung derBoc-Gruppe ohne Deblockierung der 2,3-O-Isopropylidengruppe des Uridins. Eine Behandlung von2 mitTFA/H₂O (5:1) bei Zimmertemperatur für 1 Stunde führte hingegen zur Abspaltung sowohl derBoc als auch der 2,3-O-Isopropylidengruppe. DieZ-Gruppe von1 wurde durch katalytische Hydrogenolyse auf 10% Pd/C/Ammoniumformiat abgespalten.

     

Frozen state transitions in relation to freeze drying

Freeze-drying is used as a gentle dehydration method for heat sensitive materials especially in food and pharmaceutical industries. Most materials, including dissolved sugars in water, do not crystallise during freezing prior to freeze-drying. Supersaturated, freeze-concentrated solutions are amorphous materials and they solidify into a glassy state when their temperature is depressed to below the glass transition temperature,T _g. Differential scanning calorimetry has been used to show that maximally freeze-concentrated sugar solutions, when properly frozen, show during heating a glass transition,T _g , which is followed by ice melting endotherm with onset atT _m . Low molecular weight materials are difficult to freeze-dry as they have lowT _g , andT _m slightly above T _g . High molecular weight materials, such as carbohydrate polymers, exhibit improved dehydration characteristics and they have _g and _m at about the same temperature close to the melting point of pure water. The amorphous, glassy structure typical of freeze-dried materials is formed during prefreezing and retained after removal of ice and the unfrozen water from the freeze-concentrated material. Dehydration temperatures belowT _g allow removal of ice within the solid, glassy solutes, but temperatures aboveT _m result in collapse. The frozen state transitions and properties of freeze-dried materials can be shown in state diagrams which are used to derive proper freeze-drying conditions and storage requirements for various materials.     

Heterylimidazoles IV. Homolytic dissociation of hexaaryldimidazolyls and their heterocyclic analogs

The rate constants and activation energies for homolytic dissociation of 2,2-di[ ()-naphthyl]-, 2,2-diquinolinyl-, and 2,2-di(9-acridinyl)-4,4,5,5-tetraphenyldiimidazolyls in toluene in the presence of,-diphenyl--picrylhydrazine were determined. The degrees of dissociation of the diimidazolyls were found. The effect of substituents on the stability of imidazolyl radicals is discussed.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1536–1539, November, 1974.     

Synthesis and characterization of some methyl complexes of palladium(II). Part 2(1)

Summary Dichloro complexes of Pd^II, [Pd(L–L)Cl₂], where L–L=1-(thiomethyl)-2-(diphenylarsino)ethane (S–As) or 1-(thiomethyl)-2-(diphenylphosphino)ethane (S–P) andtrans-[PdL₂Cl₂], where L=diphenyl(2-phenylethyl)-phosphine (PE), diphenyl(1-naphthyl)phosphine (PN) orN-methyl-2-thiophenealdimine (SN), have been prepared and characterized. The reactions of these complexes with MeLi were investigated. The dimethyl complexes [Pd(L–L)Me₂] (L–L=S–As, S–P) and [Pd(PE)Me₂] were isolated and characterized. Reaction of [Pd(L–L)Me₂] (L–L=S–As, S–P) with HCl affords the monomethyl derivatives [Pd(L–L)Me(Cl)]. In contrast to the Pt analogues, [Pd(L–L)Me₂] and [Pd(L–L)Me(Cl)] are relatively less stable than [Pt(L–L)Me₂] and [Pt(L–L)Me(Cl)].     

Synthesis of obtusinin and 7-(3′-hydroxymethylbut-2′-enyloxy)-6-methoxy-2H-1-benzopyran-2-one

Obtusinin (1) has been synthesised by the reaction of 6-methoxy-7-(3-methylbut-2-enyloxy)-2H-1-benzopyran-2-one (3) with OsO₄. Synthesis of 7-(3-hydroxymethylbut-2-enyloxy)-6-methoxy-2H-1-benzopyran-2-one (2) has been achieved by the regiospecific oxidation of3 with SeO₂ followed by reduction of the formed aldehyde with KBH₄.

---

Synthese von Obtusinin und 7-(3-Hydroxymethylbut-2-enyloxy)-6-methoxy-2H-1-benzopyran-2-on

Zusammenfassung Obtusinin (1) wurde über 6-Methoxy-7-(3-methylbut-2-enyloxy)-2H-1-benzopyran-2-on (3) mit OsO₄ synthetisiert. Die Darstellung von 7-(3-Hydroxymethylbut-2-enyloxy)-6-methoxy-2H-1-benzopyran-2-on (2) wurde mittels regioselektiver Oxidation von3 mit SeO₂, gefolgt von Reduktion des gebildeten Aldehyds mit KBH₄, bewerkstelligt.

     

Kinetics and mechanism of nucleophilic substitution of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II) by pyridine bases

The reaction of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II), Pd(RaaiMe)Cl₂ where RaaiMe = p-R–C₆H₄N=N–C₃H₂N₂-1-Me; R = H(1), Me(2), Cl(3), with pyridine bases [RPY: R = H (a), 4-Me (b), 4-Cl (c), 2-Me (d), 2,6-Me₂ (e), 2,4,6-Me₃ (f)] has been studied spectrophotometrically in MeCN at 451 nm. The products (4) have been isolated and characterised as trans-Pd(RPy)₂Cl₂. The kinetics of the nucleophilic substitution has been examined under pseudo-first-order conditions at 298 K. A single phase reaction step has been observed for bases such as Hpy (a), 4-MePy (b) and 4-ClPy (c) and follows the rate law: rate = (a + k[RPy]²[Pd(RaaiMe)Cl₂]). The bases 2-MePy (d), 2,6-Me₂Py (e) and 2,4,6-Me₃Py (f) exhibits a bi-phasic reaction and follows the rate laws: rate–1 = (a + k[RPy][Pd(RaaiMe)Cl₂]) and rate–2 = (a + k[RPy][Pd(RaaiMe)-Cl₂]), where k is the third-order rate constant; k is the second-order first phase rate constant, k is the second-order second phase rate constant and a/a/a correspond to the solvent dependent constant of the respective reaction path. The rate data supports a nucleophilic association path. External addition of Cl^– (LiCl) suppresses the rate, which follows the order: k/k/k (3) > k/k,k (1) > k/k,k (2). The k values are linearly related to the Hammett constants. The 2-substituted pyridines (d–f) remarkably reduce the rate and show a bi-phasic reaction behaviour as compared with 4-Rpy (a–c). This is attributed to the steric effect that destabilises the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (d) > (f) > (e). The 4-substituted pyridines control the rate via an inductive effect and follow the order: (b) > (a) > (c).     

The quest for a stable silyne, RSi ≡ CR′. The effect of bulky substituents [1]

The two major fundamental obstacles which so far have prevented theisolation of stable silynes, RSiCR (1), are: (a)the existence of more stable isomers, e.g., RRC=Si: (2) and(b) their extremely facile (exothermic) dimerication. The steric andelectronic effects of various substituents R and R (R = alkoxy,alkyl, aryl and silyl; R = alkyl and aryl groups) on the stability ofRSiCR relative to the isomeric RRC=Si:(E(1-2)), and on the energy of dimerization tothe corresponding 1,3-disilacyclobutadienes (E(D)), werestudied computationally using density functional theory (DFT) and theONIOM method. The goal was to find a combination of substituents thatwill make RSiCR more stable than RRC=Si: and whichwill also prevent its dimerization. For R = R = H,E(1-2)) = 40.7 kcal/mol (i.e., 2 islower in energy than 1), and E(D) = –104.0kcal/mol. 1, R = OH, R = m-Tbt 2,6-bis[bis(silyl)methyl]phenyl, is by 11.1 kcal/mol morestable than the isomeric silylidene 2. However, thedimerization of 1, R = OH, R = m-Tbt remains highlyexothermic (by 101 kcal/mol). 1, R = R = m-Tbt and1, R = (t-Bu)₃Si, R = m-Tbt, are by 5.8 and 2.0kcal/mol, respectively, less stable than the corresponding 2.However, the dimerization of 1, R = (t-Bu)₃Si, = m-Tbt is exothermic by only 12 kcal/mol. For1, R = (t-Bu)₃Si, and R = Tbt 2,6-bis[bis(trimethylsilyl)methyl]phenyl, the corresponding1,3-disilacyclobutadiene dimer 3, dissociates spontaneously.Thus, (t-Bu₃Si)SiCTbt is predicted to be kineticallystable towards both, isomerization to (t-Bu₃Si)TbtC=Si: anddimerization to 3, making it a viable synthetic target. Thereported energies were calculated atB3LYP/6-31G^**//B3LYP/3-21G^*; good agreement is found betweenthe DFT and the ONIOM results.     

Stereochemistry of planarchiral compounds,part XIII: Crystal structure of Meso-10,10′-dibromo-2,2′-bi-(1,6-methano-[10]-annulenyl)

Summary Crystallization of the mesoform of the title compound1 from benzene-pentane in the presence of 5% of (+)(R) _p (S) _a (R) _p -1 afforded crystals, the structure of which was determined in the achiral spacegroup P2₁/a-C _2h ⁵ . The configuration (R) _p (S) _p was confirmed, the torsional angle around the 2,2-bond is 68.6° and 72.1° (C3-C2-C2-C3 and C1-C2-C2-C1, resp.). The twist of the best planes through the perimeter carbonatoms 3, 4, 5 and 7, 8, 9 (3, 4, etc., resp.) is 26.0° and 19.8°. The colours of the crystals of the stereoisomers of1 depend on the torsional angles and thereby on the conjugation of the -systems. Meso, monoclinic (70.3°): light yellow; racemate, opt. inactive (56.2°): yellow; enantiomer of the racemate (34.4°): orange (average -values).

---

Stereochemie planarchiraler Verbindungen, 13. Mitt.: Die Kristallstruktur von Meso-10,10-dibrom-2,2-bi-(1,6-methano-[10]-annulenyl)

Zusammenfassung Kristallisation der Meso-Form der Titelverbindung1 aus Benzol-Pentan in Gegenwart von 5% (+)(R) _p (S) _a (R) _p -1 lieferte Kristalle, deren Struktur in der achiralen Raumgruppe P2₁/a-C _2h ⁵ bestimmt werden konnte: Die Konfiguration (R) _p (S) _p wurde bestätigt, der Torsionswinkel um die 2,2-Bindung beträgt 68.6 bzw. 72.1° (C3-C2-C2-C3 bzw. C1-C2-C2-C1). Die Verkippung der besten Ebenen, definiert durch die Perimeter-C-Atome 3, 4, 5 und 7, 8, 9 (bzw. 3, 4, etc.) beträgt 26.0 bzw. 19.8°. Die Farben der Kristalle der Stereoisomere von1 hängen von den Torsionswinkeln und damit von der Konjugation der -Systeme ab: Meso, monoklin (70.3°): hellgelb; Racemat, opt. inaktiv (56.2°): gelb: Enantiomer des Racemates (34.4°): orange (gemittelte Werte).

     

Oxidative cyclisation of chalcones with thallium(III)nitrate: Synthesis of (Z)-2-phenylmethylene-7-nitro-3(2H)-benzofuranones

Oxidation of 2-hydroxy-3-nitrochalcones with thallium(III) nitrate gives (Z)-2-phenylmethylene-7-nitrobenzofuran-3(2H)-one derivatives, rather than the more usual 1,2-diaryl-3,3-dimethoxypropan-1-ones or the corresponding isoflavones.

---

Oxydative Cyclisierung von Chalconen mit Thallium(III)nitrat: Synthese von (Z)-2-Phenylmethylen-7-nitro-3(2H)-benzofuranonen (Kurze Mitteilung)

Zusammenfassung Die Oxidation von 2-Hydroxy-3-nitrochalconen mit Thallium(III)nitrat ergab (Z)-2-Phenylmethylen-7-nitro-3(2H)-benzofuranon-Derivate und nicht die üblichen 1,2-Diaryl-3,3-dimethoxypropan-1-one bzw. die entsprechenden Isoflavone.

     

Mechanical properties of poly(vinyl methyl ether) hydrogels below and above their volume phase transition

The mechanical properties of radiation cross-linked poly(vinyl methyl ether) hydrogels below and above the volume phase transition (VPT) under isobar conditions were studied. The viscoelastic properties as a function of radiation dose, radiation source and polymer concentration at the state of irradiation were examined. Increased radiation doses led to higher cross-linking densities and higher moduli. Hydrogels irradiated with -rays were much harder than those obtained with electron beam irradiation at the same radiation dose. It was found that the modulus strongly increased by up to 1 order of magnitude at a temperature of the VPT of about 37 °C. In the collapsed state at temperatures well above the VPT a frequency dependence of the E() moduli in the range 0.1–22 Hz was detected, indicating viscoelastic behavior. To study the influence of solvent quality on the modulus of the hydrogels, rheological measurements were performed in water, 2-propanol and cyclohexane. A scaling exponent for the modulus according to de Gennes (G^2.25) was not found. Possible reasons for deviations (G^3.54) on poly(vinyl methyl ether) hydrogels were discussed in the context of deviations from ideal networks.     

Identification and determination of organic acids in cultivation medium ofPenicillium vermiculatum dang

Summary [2E,7E]-4,9-dioxo-2,7-decadienoic, [2E,7E]-9-oxo-2,7-decadienoic and [2Z,4E]-2-methyl-2,4-hexadienoic acids were isolated from the filtrate ofPenicillium vermiculatum Dang. The presence of [2E,2E,7S,7E]-4,9-dioxo-7-(4,9-dioxo-2,7-decadienoyloxy)-2-decenoic acid was confirmed by chromatography. HPLC was used for the determination of these acids in the cultivation medium.

---

Identifizierung und Bestimmung von organischen Säuren im Kultivierungsmedium vonPenicillium vermiculatum Dang

Zusammenfassung [2E,7E]-4,9-dioxo-2,7-decadiensäure, [2E,7E]-9-oxo-2,7-decadiensäure und [2Z,4E]-2-methyl-2,4-hexa-diensäure wurden aus dem Kultivierungsmedium vonPenicillium vermiculatum Dang isoliert. Die Anwesenheit von [2E,2E,7S,7E]-4,9-dioxo-7-(4,9-dioxo-2,7-decadienoyloxy)-2-decensäure wurde chromatographisch bestätigt, Im Filtrat vonP. vermiculatum wurden diese Säuren mittels HPLC analysiert.

     

New chiral acyclic analogs of 2′-deoxynucleosides

Convenient methods for the synthesis of chiral 2,3-seco-2-deoxynucleosides were developed. An isopropylidene protective group was used to block the 3,5-hydroxy groups in 2,3-seco-uridine. Conversion of the hydroxymethyl group to a methyl group was accomplished by chlorination with a mixture of CCl₄ and Ph₃P with subsequent reduction with n-Bu₃SnH. 2,3-seco-2-Deoxyuridine was obtained after deacetonation. The (S) enantiomer was similarly synthesized starting from 1-(-D-arabinofuranosyl)uracil. 3-O-tert-Butyldimethylsilyl-5-O-(p-monomethoxytrityl)-2,3-seco-2-deoxyuridine, which has optically active centers at C₍₁₎ and C₍₄₎, was also synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 822–826, June, 1988.The authors thank Professor M. Ya. Karpeiskii for his constant interest in this research.     

Polarographic behavior of 2,2′-bifuryl and 2,2′-furoin

In aqueous and aqueous-ethanolic buffer solutions at pH<9, 2, 2-bifuryl and 2, 2-furoin give two-electron polarographic electroreduction waves, the half-wave potentials of which depend on the pH. The primary product of the electroreduction of 2, 2-bifuryl is trans-1,2-dihydroxy-1,2-bis(, -furyl)ethylene, which then rearranges into 2, 2-furoin. The anode-cathode wave of 2,2-bifuryl has been studied by means of a Kalousek commutator. It has been shown that the polarographic behavior of 2,2-bifuryl and 2, 2-furoin is similar to that of benzil and benzoin, but differs from the behavior of analogs of the pyridine series.     

Synthesis of the bis(2′-chloroethyl) amide of β-(8-guanyl)propionic acid

The synthesis of -(8-guanyl)propionic acid and its chloride, methyl ester, bis(2-hydroxyethyl)amide, and bis(2-chloroethyl)amide has been effected. The latter readily rearranges under certain conditions into 2-chloroethylaminoethyl -(8-guanyl)propionate.     

Organotitanium chemistry 12. Synthesis of some new chiral cyclopentadienyl titanium and zirconium complex. The crystal structure of (S-cyclo-C4H7OCH2Cp)2TiCl2

Summary New chiral cyclopentadienyl-titanium and-zirconium complexes Cp₂TiCl₂, CpCpTiCl₂ and Cp₂ZrCl₂ (Cp=⁵ -cyclopentadienyl and Cp=substituted cyclopentadienyl), have been synthesized. The (S,S)-3 complex, which forms red plate crystals, has been studied by x-ray analysis. It belongs to the monoclinic space groupC2, witha 23.963(3),b 6.6470(6),c 12.6618(9) Å, 103.089(7)°, V=1964.4(3) ų and Z=4. The structure was relined to an R factor of 0.048 for 868 observed reflections.     

Flavonoids of Ammothamnus lehmannii. Structure of lehmannin and of ammothamnidin

The new flavanon lehmannin (I) has been isolated from the roots ofAmmothamnus lehmannii Bunge. On the basis of chemical transformations and with the aid of physicochemical characteristics it has been established that compound (I) has the structure of 2,4,7-trihydroxy-8-(2-isopropenyl-5-methylhex-4-enyl)flavanone. The alkaline cleavage of lehmannin gave ammothamnidin (V). The structure proposed previously for the chalcone ammothamnidin has been corrected. It has been shown that it has the structure of 2,2-4,4-tetrahydroxy-3-(2-isopropenyl-5-methylhex-4- enyl)chalcone. A comparative study of the¹³C NMR spectra of a number of flavanones has revealed an empirical law permitting the prediction of the presence or absence of substituents (OH and OCH₃) at C-2 from the value of the chemical shift of the signal of the C-2 carbon atom.Institute of the Chemistry of Plant Substances of the Uzbek SSR Academy of Sciences, Tashkent. I. P. Pavlov Samarkand State Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 516–524, July–August, 1987.     

Some remarks on the periodical change of the stability constants of the lanthanide complexes

The correlations between the values of the lgK (K = stability constant of the lanthanide complex) and the reciprocal of the ionic radius 1/r or the sum of the ionization potentials ₁ ³ I for the lanthanide ions were reviewed for different ligands. A straight-line relationship (lgK – lgK)/lgK vs. (1/r – 1/r)/(1/r) or vs. ( ₁ ³ I – ₁ ³ I)/ ₁ ³ I was found within the tetrads La-Nd, Gd-Ho, and Er-Lu.

---

Bemerkungen zum periodischen Wechsel der Stabilitätskonstanten von Lanthaniden-Komplexen

Zusammenfassung Es wurde eine Übersicht der Korrelationen zwischen den Werten von logK (K = Stabilitätskonstante der Lanthanidenkomplexe) und den reziproken Ionenradien 1/r oder der Summe der Ionisierungspotentiale ₁ ³ I für die Lanthanidenionen für verschiedene Liganden gegeben. Dabei wurde eine lineare Korrelation für (lgK – lgK)/lgK gegen (1/r – 1/r)/(1/r) oder gegen ( ₁ ³ I – ₁ ³ I)/_1/3 I innerhalb der Tetraden La-Nd, Gd-Ho und Er-Lu aufgefunden.

     

Reactions of pennogenin and related compounds. IV. Formation of (25R,22′R,25′R)-3β,3′β-diacetoxy-26,22′-epoxy-16,16′-bifurosta-5,20(22),5′,17′(20′)-tetraen-26′-ol from pennogenin diacetate under the action of BF3·Et2O

A new direction of the reaction of pennogenin diacetate with BF₃·Et₂O has been discovered in which a previously unknown dimeric steroid is formed — (25R,22R,25R)-3,3-diacetoxy-26,22-epoxy-16,16-bifurosta-5,20(22), 5,17(20)-tetraen-26-ol, the structure of which has been established as the result of an analysis of IR, UV,¹H and¹³C NMR, and mass spectra. A probable mechanism for the formation of the title compound from pennogenin diacetate is suggested.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, USSR Academy of Sciences, Vladivostok. Institute of Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 202–208, March–April, 1990.