Über Ptolemäische Sätze

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Zur Reaktionsweise von Enaminen mit Cyclopropenonen II

The addition of diphenylcyclopropenone 2 to several enamines 1 as described by Ciabattoni & Berchtold [1] [2] has been reinvestigated. The products which were previously postulated to be enamines of β-dicarbonylcompounds 9 to 14 have now been shown to be ‘amides’ 16 to 20 . The reaction does not take the course of a ‘C, C-insertion’, which would have been useful for ring expansion, but rather of a ‘C, N-insertion’, which attaches a C₃ side chain to the α-carbon of enamines. This conclusion was reached by new interpretations of spectral data and by chemical transformations of old and new products. In the course of this reinvestigation, a new class of products, the amino-cyclopentenones 41 , 45 and 47 , were isolated from the enamine-cyclopro-penone-reaction. Their structures were proven by spectroscopic considerations and by chemical degradation. A systematic representation of these reactions is proposed in the reaction scheme.     

Über die Ordnungszahl der Klassen Eulerscher Polyeder

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Thermal stability of surface freezing films in Ga-based alloys: an x-ray photoelectron spectroscopy and scanning tunneling microscopy study

We have investigated the thickness and surface structure of surface freezing films in Ga-Bi and Ga-Pb alloys over a wide temperature range between room temperature and the respective surface freezing transitions by x-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). For the example of a Ga-Bi alloy dilute in Bi, XPS measurements show that the surface freezing film has a nearly constant value of approximately 25 A between the surface freezing temperature of 130 degrees C and room temperature if the sample is cooled slowly (5 Kh). On heating to 130 degrees C the film thickness exhibits a clear hysteresis on melting. On quenching the alloy sample (>100 Kh) the film thickness increases by almost a factor of 10. These observations indicate that the surface freezing films are metastable. The surface structure of the surface freezing films of various Ga-rich Ga-Bi and Ga-Pb alloys has been probed for the first time by STM at different temperatures below and above the bulk eutectic point. Atomically resolved STM images show the surface structures of pure Bi (0001) and Pb (111), respectively, at room temperature. On heating above the eutectic temperature the surface structure of the films does not change significantly as judged from the size and thickness of Pb or Bi terraces. These observations together with the film thickness variation with temperature indicate that the surface freezing films behave like a metastable independent surface phase. These results together with the wetting characteristics of these alloys suggest that surface freezing in these systems is a first order surface phase transition between wetting and metastable surface freezing films. The energy barrier for nucleation is strongly reduced due to a lowering of the interfacial energy if the nucleus is completely immersed in the respective wetting layer.     

Zur Reaktionsweise von Enaminen mit Cyclopropenonen V. Einsatz von β-Carbonyl-enaminen

Diphenylcyclopropenone ( 10 ) was heated with five different β-carbonyl-enamines, namely 4-pyrrolidino-pent-3 E-en-2-one ( 12 ), 4-dimethylamino-pent-3E-en-2-one ( 13 ), 4-dimethylamino-but-E-en-2-one ( 14 ), 3-dimethylamino-1-phenyl-prop-E-en-1-one ( 15 ) and ethyl 3-pyrrolidino-isocrotonate ( 16 ). The resulting reactions were more sluggish than those of 10 with ordinary enamines. The main reaction (between 10 and 69% yield) was in all cases a ‘C, N-insertion’. The major products were: from 12 : an inseparable mixture of 4-methyl-6-oxo-2,3-diphenyl-hepta-2E, 4E-dienoic acid pyrrolidide ( 17 ) and its 2Z, 4E-stereomer ( 18 ); from 13 : 4-methyl-6-oxo-2, 3-diphenyl-hepta-2E-dienoic acid dimethylamide ( 19 ) and its 2Z, 4E-stereomer ( 20 ); from 14 : 6-oxo-2, 3-diphenyl-hepta-2E, 4E-dienoic acid dimethylamide ( 21 ); from 15 : 6-oxo-2,3,6-triphenyl-hexa-2E, 4E-dienoic acid dimethylamide ( 22 ); and from 16 : 5-ethoxycarbonyl-4-methyl-2, 3-diphenyl-penta-2E, 4E-dienoic acid pyrrolidide ( 23 ) and its 2Z, 4E-stereomer ( 24 ). The constitutions of 17 to 24 were derived mainly from spectral properties. For these products the E-configuration at the 4,5-double bond was assigned on the assumption that the insertion of the side-chain (cyclopropenone carbons) between the enamine carbon and nitrogen atoms occurred with retention of configuration, as had been concluded earlier. This was confirmed in the cases of 21 and 22 by the trans-coupling between H? C(4) and H? C(5) in the ¹H? NMR. spectrum, the educts ( 14 and 15 ) having the E-configuration. The configurational difference between the stereomeric products 17 / 18 , 19 / 20 and 23 / 24 was, therefore attributed to the 2,3-double bond. This was confirmed by aqueous acid treatment in the case of the pair 19 / 20 : The 2E-configuration for 19 followed from its conversion to 4-acetonyl-4-methyl- 2,3-diphenyl-isocrotonolactone ( 25 ) and the 2Z-configuration of 20 by its conversion first to a mixture ol two diastereomers of (presumably) 1-acetyl-4-dimethylaminocarbonyl-2-methyl-3- phenyl-l,4-dihydronaphthalene ( 27a ) and then, under more drastic conditions, to 6-methyl-11H-benzo[a]fluorene ( 26 ).The structures of 25 and of 26 were derived from their spectral properties, and that of the 27a -mixture was made probable by the plausibility of its intermediacy on the way to 26 . A pathway for the conversion of 20 to 27a (scheme 3) and of the latter to 26 (scheme 4)is proposed. In the case of the reaction of 10 with 12 , two stereomeric basic by-products were isolated (combined yield 150/,). Their structures as traw- and cis-4-acetonyl-4,5-diphenyl-3-pyrrolidinocyclopent-2-en-ones ( 30 and 31 ) were deduced from their spectral properties and from those of their hydrochlorides 32 and 33 . The enamino-ketone function was found to be resistant to a number of reagents, among which were excess sodium borohydride, which converted 30 to the secondary alcohol 34 , and excess methyllithium, which converted 31 to the tertiary alcohol 35 . A mechanism (called ‘rearrangement’) is proposed (scheme 5) for the formation of the enaminoketones (such as 30 and 31 ), which proceeds via the same ammonio-enolate intermediate ( 36 ) which plays a role in the formation of the major products, the amides (such as 17 to 24 ). It is suggested (scheme 6) that the 3-membered ring of the ammonio-enolate 40 may open in three ways, one of which leads to the amides and another to the enamino-ketones.     

Butanolide und Butenolide durch intramolekulare En-Reaktion bei der Thermolyse von Propargyl-propiolaten

Butanolides and Butenolides by Intramolecular Ene-Reaction during Thermolysis of Propargyl Propiolates Gas-phase flow thermolysis of 2-butynyl propynoate ( 1 ) and 2-propynyl 2-butynoate ( 2 ) at 550° afforded 3-ethynyl-2-methyl-2-buten-4-olide ( 4 , 85%) and 2-ethynyl-3-methyl-2-buten-4-olide ( 5 , 80%), respectively. Their formation presumably entails an ene reaction between the methylacetylenic and the acetylenic functions of the diyne esters 1 and 2 to give the two methyliden-vinyliden-butanolides 10 and 11 as intermediates, followed by a [1,5]-H shift to 4 and 5 . At 400–450°, the gas phase flow thermolysis of 1 and 2 led to the dimers 16 (77%) and 17 (6%), respectively. These products resulted from the Diels-Alder dimerization of the above mentioned intermediates 10 and 11 . The regioselectivity of this dimerization is determined by a ‘head-to-head’ approach, with the double bond conjugated to the carbonyl group acting as the dienophile in both cases. The low yield of 17 from 2 is probably due to a further Diels-Alder reaction of the dimer 17 with its precursor 11 , yielding a trimer 18 (8% isolated). This process is not possible when starting with 1 , which explains the higher yield of 16 . The gas phase flow thermolysis of 2-butynyl 2-butynoate ( 3 ) at 550° afforded a mixture of four isomeric products, namely the two monocyclic ethynyl-butenolides 6 and 7 and the two bicyclic vinyl-butenolides 8 and 9 . The formations of 6–9 are also rationalizable by initial ene-reactions, in this case two alternative ones, each involving one of the two CH₃ groups of 3 . This leads to two alkylidene-vinylidene-butenolides, namely 12 and 13 . A [1,5]-H shift converts 12 into 6 and 13 into 7 . A competing alternative [1,5]-H shift transforms both 12 and 13 to the triene 14 , which electrocyclizes to the cyclohexadiene 15 . The latter undergoes two alternative [1,5]-H shifts to yield 8 and 9 .     

Harnuntersuchung

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