✍ Scribed by Anne Andrée Sophie Briquet; Hans-Jürgen Hansen
No coin nor oath required. For personal study only.
The synthesis of 1-and 2-aryl-substituted (aryl = Ph, 4-N0,-C6H,, and 4-MeO-C6H4) 4,6,8-trimethylazulenes (4 and 3, respectively) in moderate yields by direct arylation of 4,6,8-trimethylazulene (8) with the corresponding arylhydrazines 13 in the presence of Cu" ions in pyridine (see Scheme 4 ) as well as with 4-MeO-C,H4Pb(OAc), (1 6 ) in CF,COOH (see Scheme 5 ) is described. With 13, also small amounts of 1.2-and 1.3-diarylated azulenes (see 14 and 15, respectively, in Scheme 4 ) are formed. The 4-methoxyphenylation of 8 with 16 yielded also the 1,l'-biazulene 17 in minor amounts (see Scheme 5 ) . 4,6,8-Trimethyl-2-phenylazulene (3a) was also obtained as the sole product in moderate yields by the reaction of sodium phenylcyclopentadienide (la) with 2,4,6trimethylpyrylium tetrafluoroborate (2) in THF (Scheme I ). The attempted phenylation of 8 as well as of azulene (9) itself with N-nitroso-N-phenylacetamide (10) led only to the formation of the corresponding 1-(pheny1azo)substituted azulenes 12 and 11, respectively (Scheme 3 ) .
-In most of the aryl-substituted azulenes that have been prepared in the nearly 60-year-old history of azulene synthesis (cf. [I] [2]), the aryl groups were already present in the reactants that were combined to azulenes'). A direct arylation method of azulenes has been developed by Hufner et at. who showed that aryllithium derivatives can be added directly to the seven-membered ring of azulenes. The dihydroazulenes, formed as intermediates, can easily be dehydrogenated to the corresponding azulenes. However, this LUMO(azu1ene)-controlled reaction allows the nucleophilic addition only at C(4), C(6). and C(8). Also the reaction of diethyl azulene-1,3-dicarboxylate or of its 2-chloro derivative with aryl-Grignard reagents leads mainly to the formation of the corresponding 4-and 6-arylated azulene-l,3-dicarboxylate [2 11. However, diethyl 2-methoxyazulene-l,3-dicarboxylate is first phenylated at C(2) and than mainly at C(4) with PhMgBr [21].
In the course of our investigations of possible thermo-and photochromisms of heptalenes , we were interested in the synthesis of 4and 5-aryl-substituted heptalene-1,2-dicarboxylates with at least three substituents in the peri-positions to slow down the thermal C=C bond shift in these heptalenes (see . Starting materials for the synthesis of these heptalenes should be the corresponding 1-and 2-aryl-substituted
Part of the Ph. D. thesis of A.A.S.B., University of Zurich, 1993. This is also true for the very first synthesis of Pfau and Plattner which yielded inter alia 4-phenylazulene and served as proof for the structure of azulenes. Further syntheses of azulenes with aryl substituents at the five-as well as at the seven-membered ring have been performed by Plattner et af. [4] [5], Pommer [6], Hajner and Kaiser [7], Nozoe et al. [8] [9], Yasumani et af. [lo] [ll], Gassman et af. [12] [13], Copland et al. [14] as well as Houk et af. [15]. In a further variant, Jutz and Schweiger assembled the Ph and l,l'-biphenyl-4-yl group directly at the skeleton of 6-methylazulene [16]. ' ) 6, Similar results have been reported by Nefedov et al. [34]. Nefedov et al. [34] observed also the formation of 1,2-diphenylazulene in the arylation reaction of azulene (9).
📜 SIMILAR VOLUMES
drrr tizssberg. 3400 Corringen. Federal Republic of Germany A d&> cd lluorc,cence S2 -So from the second exited singlet state (Sz) of4.6,8-trimethylazulene (TMA), resulting lrum tlolrlo-triplet-triplcr annihilation Tt + Tt --S2 + So, has been observed. No delayed fluorescence from an upper es-r~mcr