2,T-Bipyridyl konnte erstmals nucleophil alkyliert werden. Bei der Umsetzung mit Methyl-und n-Butyllithium entstand je nach den Bedingungen sehr selektiv die 6-Alkyl-oder 6,6-Dialkyl-Verbindung (41 -64 %). Die Anwendung relativ tiefer Temperaturen erlaubte in mittlerer Ausbeute auch die Darstellung von CAryl-Verbindungen (Aryl = Phenyl, 2-Pyridyl). Im Konkurrenzversuch zeigte 2,T-Bipyridyl gegeniiber n-Butyllithium deutlich hohere elektrophile Aktivitat als Pyridin.
Protophanes and Polyaromatics, XXII"Nucleophilic Alkylation and Arylation of 2,2'-Bipyridyl 2,Z'-Bipyridyl was alkylated by nucleophilic substitution for the first time. The reaction with methylor n-butyllithium yielded very selectively either the 6-alkyl-or the 6,6'-dialkyl compound (41 -64 %) depending on the conditions. Applying relatively low temperatures it was possible to prepare 6-aryl-2,2-bipyridyIs (aryl = phenyl, 2-pyridyl) in medium yields. In a competition experiment with n-butyllithium 2,2'-bipyridyl was significantly more electrophilic than pyridine.Ziegler und Zeiser 1 ') XXI.
Of particular interest are the syntheses of the o-bis(trimethy1silyl) derivatives ( 3 r ) and ( 4 e ) . Although quite strained, these compounds form in relatively high yield because bistrimethylsilylacetylene does not trimerize under the reaction conditions[ld. 91. Thus, slow addition of the diyne (1) to the alkyne ( 2 ) in this case leads to more efficient cocyclization, although side reactions are not entirely suppressed.
Heteropolyaromaten, bei denen die nichtterminalen Aromateneinheiten jeweils mit zwei orthostandigen aromatischen Kettengliedern verkniipft sind (2a -e, 3a, b, 4a -e, 5a -c, 8), erleiden im Massenspektrometer in hohem Mane Spaltung zwischen den Aromateneinheiten. Hierfiir wird ein Additions-Eliminierungs-Mechanismus postuliert , der zur Ausbildung eines neuen sechsgliedrigen Ringes im kationischen Fragment fiihrt und durch eine spiralige Sekundarstruktur der Polyaromaten begiinstigt ist. -Die Synthese von sechs Heterotetraaromaten (2a -e, 3a) wird beschrieben.
Protophanes and Polyaromatics, XXVII l)
Fragmentation in the Mass Spectrometry of Heteropolyaromatics; New Examples of the Mass Spectrometric ortho-EffectHeteropolyaromatics, the nonterminal aromatic units of which are connected in ortho-position with other aromatic members of the chain (2a-e, 3a, b, 4a-e, 5 a -c , 8), suffer in the mass spectrometer fission between the aromatic units in high degree. An addition-elimination mechanism is postulated which brings about a new six-membered ring in the cationic fragment and is favored by a helical secondary structure of the polyaromatics. -The synthesis of six heterotetraaromatics (2a-e, 3a) is described.In den Massenspektren (70 eV) von Heteropolyaromaten werden Fragment-Ionen, die durch Sprengung der Bindungen zwischen den Ringen entstehen, nach unseren Er-
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