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A product, " Dianin's compound,'' first prepared in 1914 from phenol and mesityl oxide, is shown to be 4-P-hydroxyphenyl-2 : 2 : 4-trimethylchroman (111). Oxidation yields 2 : 2 : 4-trimethylchroman-4-carboxylic acid, and thermal degradation gives phencl and 2 : 2 : 4-trimethylchromen. The latter compound has been synthesised and yields Dianin's compound by addition of phenol.Dianin's compound forms inclusion compounds with over fifty widely differing organic solvents, some inorganic gases, and with iodine. The large, separate cavities in the crystals are defined by six molecules of Dianin's compound, and the ratio of number of molecules of Dianin's compound to the number of included molecules is generally 6 : 1, though a ratio of 3 : 1, i.e., 2 molecules per hole, is found with a number of small molecules.PREVIOUS papers 1, have described inter al. some derivatives of 2'-hydroxy-2 : 4 : 4-trimethylflavan prepared by condensing simple phenols with acetone, and these flavans formed inclusion compounds with a variety of organic solvents.2* The condensation product of phenol with mesityl oxide was studied by Dianin: and he observed that it formed crystalline adducts with certain organic solvents. We have now reinvestigated this substance, which will be referred to as " Dianin's compound " (see a preliminary note by Baker and McOmie 7.Dianin showed that phenol (2 mol.) reacted with mesityl oxide (1 mol.) in presence of hydrogen chloride to give a monohydric phenol, C18H2002, which formed a benzoate and a *

previously found at room temperature""], the C3-C3' bridge bond length (1.417 A, Fig. Id) is remarkably short. Fig. I. Electron density distribution in the bonds of 1 aqd bond lengths [A] at -155 "C. The contours are drawn at intervals of 0.05 eA-' and the standard deviation of the bond lengths is 0.001 A. The atoms are not numbered in accordance with IUPAC rules. Crystallographic data of 1 (C,H,O): for data at room temperature see [11; at -155 "C: a = 10.7598(7), b=6.8256(4), c=8.396(1)A,,!3=110.999(5)": C2/c;2=4. Up tosinO/A=1.15 k ' ( M o K ,radiation) 1968 independent, repeatedly measured reflections (248 of which were unobserved, F,, <2.5a(E,)) were collected; the C and 0 atoms were refined with 1028 reflections of higher order (0.70

Es wird die Totalsynthese des linearen Peptidalkaloids Hexaacetylcelenamid A (7) beschrieben. Schlüsselreaktionen sind zwei Kondensationen mit α‐(Dialkylphoshoryl)aminosäurederivaten 10 zum Aufbau der Dehydroaminosäure‐ und Dehydropeptidderivate 14 bzw. 17.

rate with high vapor pressure at T>2500"C, thus accounting for their low content; the high melting impurities Ta and W, on the other hand, remain in the niobium. The samples R-Nb-1 were electrolyzed; the major impurities Ta and W are thus removed, but metals such as Cr, Fe, and Co are apparently involved by contamination. The samples R-Nb-2 were additionally zone refined and annealed, which leads to a marked decrease in the Cr, Fe, and Co content.The niobium thus obtained can be additionally characterized by its specific electrical resistivity of @ (4.2 K)=6 x 0 cm in the normal state; the total content of non-metals is about 100 ppb. These findings show that niobium of particularly high purity and structural perfection can be prepared by the above method. The analytical method developed here for the determination of Cr, Fe, and Co is characterized by its extremely high sensitivity and freedom from error regarding contamination and losses.

both the pure Eas well as the pure Z-isomer of the cyclic phosphinate l a with trifluoroacetate acid'']. 2a adds nucleophiles such as water, methanol or ethanol at C-4 to give the E/Z-mixture 3s (R= H, Me, Et); hydride ions add at C-2 to give the E/Z-mixture 4a.The 57c delocalization, competing for the destabilization by the phosphinic acid group, accounts for the stability of the carbocation of 2. The species 2b is kno~n['"~~]. Recent, independent experiment^[^*^' encouraged us to prepare the salts 2c and 26 (containing deep-blue and deep-red cations, respectively161) from l c and Id by reaction with trifluoroacetic acid or aluminum chloride in dichloromethane. 2c and 2d likewise add nucleophiles such as water, methanol or ethanol to give the E/Z mixture of 3c and 3d, respectively (R=H, Me, Et); hydride ions add to C-2 to give 4c and 46, respectively. 4c and 4d react with potassium hydride in tetrahydrofuran (THF) to give the salts 5c and 5d containing stable delocalized anions. A mixture of equimolar amounts of 2c and 2d in dichloromethane and of 5c and 5d, respectively, in THF at room temperature, leads to formation of the radicals 6c and 6d, respectively, which are stable for days in the absence of air; their phosphorus coupling constants up=2.3 mT compare very well with those of the well known radicals 6a (u,=2.31 m v , and 6, R' = tBu, R2 = C6H3(tBu),(3,5) (up = 2.35 I~T)['~. Angew. Chem. Int. Ed. Engl. 23 (1984) No. I 2 0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984 0570-0833/84/12 12-0993 $ 02.50/0

Es wird die Totalsynthese des linearen Peptidalkaloids Hexaacetylcelenamid A (7) beschrieben. Schlusselreaktionen sind zwei Kondensationen mit a-(Dialkylphosphory1)aminosiiurederivaten 10 zum Aufbau der Dehydroaminosiure-und Dehydropeptidderivate 14 bzw. 17.