Versuche zur Synthese von Calicen aus trisubstituierten Cyclopropanen und Cyclopentenon

Attempted Synthesis of Calicene from Trisubstitued Cyclopropanes and Cyclopentenone The Li carbenoids 4 , prepared by treatment of substituted 1,1-dihalocyclopropanes with BuLi, are reacted with cyclopent-2-enone under thermodynamic and kinetic control (Scheme 1). In general, the latter procedure gives better yields of cyclopropylcyclopentenols 5a – e , but the reaction seems to be controlled mainly by the steric and electronic properties of the substituent Y. So, with 4b and 4e , the main reaction is the attack of the carbenoid at C(1) of cyclopent-2-enone, while 4a (Y = PhS) predominantly deprotonates the ketone (Scheme 4). Whereas 5d and 5e can easily be converted to the dihydrocalicenes 6d and 6e (Scheme 6), the attempted elimination of H₂O from 5a – c leads to the rearranged products 13 – 2 due to the opening of the cyclopropane ring (Scheme 5). Finally, the generation of the parent compound 2 from the silylated precursor 6d is attempted: treatment with MeO^? gives the addition products 18A/18B , while the reaction with Br₂ provides 19 by a bromination/dehydrobromination sequence (Scheme 7).     

Irren ist menschlich – oder: Der Satz über die Unimodalität stabiler Verteilungen, ein Theorem mit einer bewegten Geschichte

Zusammenfassung. Wohl wenige der bekannteren S?tze der Mathematik haben eine derart wechselvolle Geschichte hinter sich wie das Theorem über die Unimodalit?t (d.h. „Eingipfligkeit”) stabiler Wahrscheinlichkeitsverteilungen. Von der ersten Behauptung durch Lévy bis zum endgültigen Beweis vergingen über 40 Jahre. Publiziert worden sind zwei falsche Beweise und ein falsches Gegenbeispiel; beteiligt waren unter anderem Leute wie Gnedenko, Kolmogorov und Ibragimov, also Mathematiker h?chster Reputation! Ziel dieses Artikels ist es, die historische Entwicklung des erw?hnten Problems nachzuzeichnen, die verschiedenen Beweisversuche zu beschreiben und insbesondere zu zeigen, wie die Fehler entstanden sind. Eingegangen am 5. Januar 1999 / Angenommen am 23. Juni 1999     

Umlagerung von 5-Amino-5-X-pentadienalen zu 2-Aminopyrylium-Salzen

Rearrangement of 5-Amino-5-X-pentadienals to 2-Aminopyrylium Salts Various 2-aminopyrylium salts 7 (X=Cl, Br, I) are available in a simple one-pot procedure by reacting `push-pull' enynes 5 with equivalent amounts of HCl, HBr, or HI. On the other hand, reaction of HF or AcOH with `push-pull' enynes 5 is considerably slower so that an excess of HF or AcOH is needed for the reaction to 7 (X=F, AcO). The 2-aminopyrylium salts 7 are the key intermediates in the postulated rearrangement of 5-amino-5-halogeno-pentadienals 6 to 5-halogenopenta-2,4-dienamides 8 (Scheme 1, bottom), which is vinylogous to the well-known rearrangement of 3-amino-3-X-propenals 2 to 3-X-propenamides 3 (Scheme 1, top).     

Management of Vocal Fold Scar with Autologous Fat Implantation: Perceptual Results

Vocal fold scar disrupts the mucosal wave and interferes with glottic closure. Treatment involves a multidisciplinary approach that includes voice therapy, medical management, and sometimes surgery. We reviewed the records of the first eight patients who underwent autologous fat implantation for vocal fold scar. Information on the etiology of scar, physical findings, and prior interventions were collected. Videotapes of videostroboscopic findings and perceptual voice ratings [Grade, Roughness, Breathiness, Asthenia, Strain (GRBAS)] were randomized and analyzed independently by four blinded observers. Etiology of scar included mass excision (7), vocal fold stripping (3), congenital sulcus (2), and hemorrhage (1). Prior surgical procedures performed included thyroplasty (1), autologous fat injection (9), excision of scar (2), and lysis of adhesions (2). Strobovideolaryngoscopy: Statistically significant improvement was found in glottic closure, mucosal wave, and stiffness (P = 0.05). Perceptual ratings (GRBAS): Statistically significant improvement was found in all five parameters, including overall Grade, Roughness, Breathiness, Asthenia, and Strain (P = 0.05). Patients appear to have improved vocal fold function and quality of voice after autologous fat implantation in the vocal fold. Autologous fat implantation is an important adjunctive procedure in the management of vocal fold scar, and a useful addition to the armamentarium of the experienced phonomicrosurgeon.     

Überraschende Reaktion von 5‐(Phenylthio)‐ und 5‐(Methylthio)pent‐ 2‐en‐4‐inal mit HCl

Surprising Reaction of 5‐(Phenylthio)‐ and 5‐(Methylthio)pent‐2‐en‐4‐inal with HCl Contrary to expectations (Scheme 1), 5‐(phenylthio)‐( 1a ) as well as 5‐(methylthio)pent‐2‐en‐4‐inal ( 1b ) react with a slight excess of HCl to give 2‐[bis(phenylthio)methyl]furan ( 17a , 77% yield) and 2‐[bis(methylthio)methyl]furan ( 17b , 61% yield), respectively. Structures 17a and 17b are supported by the results of an X‐ray crystal‐structure analysis, by spectroscopic data in comparison to those of model compounds, and by synthesis of 17a . This surprising reaction is tentatively explained by a mechanism (Scheme 4), including a special pyran→furan ring‐contraction sequence, which is in agreement with a labelling experiment.     

Synthese von gestapelten `Push-Pull'-Acetylenen

Synthesis of Stacked `Push-Pull' Acetylenes. In view of possible solid-state polymerizations of crystalline stacked `push-pull'-acetylenes 1 , a series of compounds 1 has been synthesized (Scheme 3), and the results of X-ray analyses of `push-pull'-acetylenes 1d , e , f are discussed. Of these three compounds, methyl 2-morpholinoacetylene carboxylate ( 1d ) is by far the best candidate giving crystals with nicely stacked molecules (Fig. 3). Even in this case, however, stacking parameters d=4,12 Å and α=31,6° are too large for allowing solid-state polymerizations.     

Versuche zur Synthese von [2.2]- und [2.3]Cyclopentadienophanen

Synthetic Attempts towards [2.2]- and [2.3]Cyclopentadienophanes . The first [2.2]Cyclopentadienophane (=2,2,3,3,8,8,9,9-octamethyltricyclo[8.2.1.1^4,7]tetradecatetraene; 1b ) has been synthesized (Scheme 5) by reductive coupling of 6,6-dimethylfulvene 3 → 5 (50%) followed by base-induced twofold condensation of 1,2-di(cyclopentadienyl)-1,2-dimethylbutane 5 with acetone to give difulvene 15 (95%). Reductive coupling of 15 gives a complex mixture of tautomers of 16 , 17 , and 1b , which contains ca. 50% of the target molecule 1b . Other synthetic attempts towards [2.2]cyclopentadienophanes 1a and 1b and [2.3]cyclopentadienophane 18 are discussed.     

Synthese von funktionalisierten Bi(cyclopropylidenen)

Synthesis of Functionalized Bi(cyclopropylidenes) In view of the synthesis of attractive triafulvalene precursors 9 , a series of bi(cyclopropylidenes) 8 with vinyl- ( 8a ), alkoxycarbonyl ( 8c – f ), hydroxymethyl ( 8h ), as well as protected hydroxymethyl groups ( 8g , 8i ) have been prepared by simple one-pot reactions of the corresponding 1,2-dibromo-cyclopropanes 6 with BuLi/CuCl₂ at −95°. First experiments towards a direct low-temperature synthesis of bi(cyclopropylidenes) bearing good leaving groups 9k (X=AcO) and 9l (X=Br) are reported.     

Synthesis of Novel Precursors of Calicene and 7‐Methylcalicene

Cyclopent‐2‐en‐1‐one is a versatile electrophilic cyclopentadiene equivalent in reactions with 1‐bromo‐1‐lithiocyclopropanes. The synthetic sequence (outlined in Scheme 1) has been applied to the synthesis of functionalized 7‐X‐7,8‐dihydrocalicenes 13c (Scheme 3) and 13d (Scheme 4). 7‐Bromo‐7,8‐dihydrocalicene ( 13d ) is considered to be a promising precursor of the so far unknown parent calicene ( 2 ). A similar sequence has been realized for 7‐(chloromethyl)‐7,8‐dihydrocalicene ( 21a , Scheme 5) which, under appropriate conditions, could give 7‐methylcalicene ( 16 ).