Annulenes, synthesis

Azamethano[ 10]annulenes synthesis, 3, 424 Azamethine dyes stabilizers... 

Scheme 3. Intramolecular acetylenic coupling in annulene synthesis described by Sondheimer[8] according to the method of Eglinton and Galbraith [7],...

M. J. Marsella, G. Piao and F. S. Tham, Expanding tetra[2,3-thienylene]-based molecular muscles to larger [4n]annulenes, Synthesis, 9, 1133-1135 (2002). 

Mitchell RH, Carruthers RJ, Mazuch L, Dingle TW (1982) Toward the Understanding of Benzannelated Annulenes — Synthesis and Properties 01 [a]—Ring Monobenzannelated Dihydropyrenes. J Am Chem Soc 104 2544... 

Azaadamantanes biocide, 1, 400 mechanism, 1, 401 photoelectron spectroscopy, 2, 142 5-Azaadenines reactions, 5, 878 synthesis, 5, 901 8-Azaadenosines synthesis, 5, 895 Azaallyl cations generation, 7, 73 Aza[10]annulenes bridged... 

Heteroannulenes electrophilic reactions, 7, 726 tr-excessive synthesis, 7, 727 nucleophilic reactions, 7, 727 Hetero[l IJannulenes structure, 7, 715 Hetero[ 12]annulenes pyridine-like methano-bridged, 7, 715 Hetero[ 13]annulenes unrestricted structure, 7, 716... 

Obidoxime chloride as insecticide, 2, 516 Obtusilactone H NMR, 4, 578 Occidentalol synthesis, 1, 472 Octaaza[14]annulenes bis w-excessive, 7, 717 Octacoral... 

The 7/NMR spectrum displays signals of shielded protons = - 2.35, integral level 1) and of deshielded ones = 10.45 and 9.39, integral levels 1 1). This reflects a ring current due to aromaticity as described for annulenes and porphyrins in section 2.5.2. To conclude, the reaction involves an oxidative cyclisatlon of 2,5-bis(2-pyrrolylmethyl)-17/-pyrrole 2 with 47/-trlazole-3,5-dlaldehyde 3 to the corresponding 2,3-diazaporphyrin 4, following the 3-t-l pathway of porphyrin synthesis. Two non-equivalent tautomers may exist these are the diaza[ 18]annulene 4a and the tetraaza[18]annulene 4b. 

The term annulene was coined to refer to the completely conjugated monocyclic polyenes. The synthesis of annulenes has been extended well beyond the first two members of the series [4]annulene (cyclobutadiene) and [6]annulene (benzene). The generality of the Hiickel rule can be tested by considering the properties of members of the annulene series. 

The synthesis of annulenes has been carried forward to larger rings as well. 

Badger and coworkers devised a sequential synthesis of [ 18]annulene-l,4 7,10 l 3,16-trioxide which is formally the condensation product of three furan molecules and three ethylenes . The synthesis is illustrated below in Eq. (3.25). The [18]annulene trioxide was obtained as a red solid (mp 215—216 °d) whose proton nmr spectrum showed two peaks of equal area at 8.66 and 8.68 ppm. 

Another application of this method is the synthesis of 5,10-epoxy[10]annulene (7) from 2,3.6,7-tetrabromo-4a,8a-epoxydecahydronaphthalene.152-154 The byproduct is 1-benzoxepin (8). The 5,10-cpoxyannulcnc (7) incorporates the oxepin structure. The annulene can be converted to 1-benzoxepin by proton catalysis.153154... 

Cyclazines may be considered as nitrogen-bridged annulenes rather than as hetarenes and, therefore, are only briefly mentioned in this volume. The chemistry of [3.3.3]cyclazines 1 and aza analogs, e. g. 3, is covered comprehensively in Houben-Weyl, Vol. E7b, p 205 IT. For another recent review, see ref 1. Subsequently, the chemistry of individual types of cyclazines has been reviewed, in particular 2.2.x]cyclazines,1 2 [2.2.2]cyclazines,3 [2.3.x]cyclazines4 and [2.2.3]-cyclazines.5 Moreover, the synthesis and the reactions of [2.2.3]cyclazines and the question of the effect of bcnzannulation have been addressed specifically.6... 

The preparation of l,6-oxido[10]annulene, described simultaneously by Sondheimer and Shani4 0 and by Vogel, Biskup, Pretzer, and Boll, is illustrative of the rather general synthesis of aromatic 1,6-bridged [10]annulenes starting from 1,4,5,8-tetrahydronaphthalene. Apart from the present compound, the following bridged [10]annulenes have thus far been obtained by this approach l,6-methano[10J-annulene,2-8-9 the ll,ll-dihalo-l,6-methano[10]annulenes,9 10 and 1,6-imino [ 1 OJannulene.11... 

The first step in this preparation, the epoxidation of 1,4,5,8-tetra-hydronaphthalene, exemplifies the well-known selectivity exerted by peracids in their reaction with alkenes possessing double bonds that differ in the degree of alkyl substitution.12 As regards the method of aromatization employed in the conversion of ll-oxatricyclo[4.4.1.01-6]-undeca-3,8-diene to l,6-oxido[10]annulene, the two-step bromination-dehydrobromination sequence is given preference to the one-step DDQ-dehydrogenation, which was advantageously applied in the synthesis of l,6-metliano[10]annulene,2,9 since it affords the product in higher yield and purity. 

The recent upsurge of interest in systems of theoretical interest demands practical syntheses of several important compounds. These are BICYCLO[2.l.0]PENT-2-ENE, BENZOCYCLOPROPENE, 1,6-OXIDO[10]ANNULENE, and others. ewdo-TRICYCLO[4.4.0.02 5]-DECA-3,8-DIENE-7,10-DIONE is utilized as a model for the use of CYCLOBUTADIENE IN SYNTHESIS, and a stable monomeric ketene, icri-BUTYLCYANOKETENE offers opportunities for further studies of this interesting species. 

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