O-Diethynylbenzene

Surprisingly, the simplest graphdiyne model, PDM 1, had eluded synthesis. Even though substituted derivatives (e. g. 75,85) have been prepared by the standard cyclooligomerization reaction of o-diethynylbenzenes, isolation of the parent molecule failed via this method [8,51]. Utilization of an intramolecular... 

Another limitation of the traditional Cu-mediated cyclooligomerization reaction is generation of differentially substituted PDMs. In the above case, the substitution pattern in the starting o-diethynylbenzene must be maintained on each and every benzene moiety in the oligomeric mixture of PDMs that is produced. Thus, it is impossible to prepare less symmetric systems like 100 via this route. With the intramolecular synthetic approach, however, it should be possi-... 

Intramolecular cyclization of o-diethynylbenzene gives us an opportunity to compare results of the thermal and cation-radical variants of the reaction. There are three possible modes of cyclization shown in Scheme 7.25. 

Although the 1,6 cyclization takes place in the thermal process, the cation-radical initiation leads to the 1,5 cyclization (Ramkumar et al. 1996). Chemical oxidation of o-diethynylbenzene bearing two terminal phenyl groups by tris(p-bromophenyl)ammoniumyl hexachloroantimonate as the catalytic oxidizing agent in the presence of oxygen yields 3-benzoyl-2-phenylindenone in 70% yield (Scheme 7.26). 

Scheme 7.26 reflects the final result of the reaction. The initial step of this reaction consists of one-electron oxidation of the substrate. The resulting cation-radical of o-diethynylbenzene transforms into a fulvenyl intermediate, which further reacts with the neutral substrate to yield fulvenyl... 

According to the authors, the 1,5-cyclization mode of o-diethynylbenzene (see Scheme 7.25) is determined by electron state symmetry, which is different from that of the neutral molecule of o-diethynylbenzene (Ramkumar et al. 1996). 

Benzotellurepine has been prepared by the addition of Na2Te to o-diethynylbenzene in the presence of hydrazine hydrate, under PTC conditions. The compound is quite unstable but is converted into the more stable dihalides by treatment with SOjClj or Br2- The dihalides regenerate the tellurepine by reduction with NajS. ... 

Riphenylenes.1 o-Diethynylbenzene (l)2 cocyclizes with monoalkynes in the presence of this cobalt catalyst to furnish biphenylenes (2). The yield of 2 is high when... 

Ultraviolet irradiation of dialkynylbenzenes produces polymers along with small amounts of dimers. The dimer fraction consists of azulenes and, in some cases, naphthalenes. The product distribution in the dimer fraction depends on the relative orientation of the alkynyl groups as well as the substituents on the alkynyl groups and on the ring. o-Diethynylbenzene (365) produces azulenes 366 and 367 while p-diethynylbenzene yields 368 and 369 These products can be accounted for in... 

An azulene (36) having two intramolecularly crossing ethynyl groups was obtained together with its isomer (37) on irradiation of o-diethynylbenzene (35) and no further photochemical reaction was observed . On the other hand, o-bisphenyl-ethynylbenzcne (38) gave an azulenophenalene system, verdene (39), on irradiation . The mechanism of the formation of 39 was considered as a result of further cycloaddition of two triple bonds crossed in an intermediate azulene derivative (40). This photochemical reaction is reminiscent of the Biichi reaction in which diphenyl-acetylene yields an azulene system. 

The disadvantage of this route is the required multistep synthesis of o-diethynylbenzene. 

In many cases, e.g., with o-divinylbenzene or o-diethynylbenzene, monomeric as well as polymeric cyclic adducts can be isolated.439... 

The effect on the Bergman cycloaromatization of sulfur-containing substituents in the acetylene branch was studied for simple models, such as butyl-2-(triisopropylsilylethynyl)phenylethynylsulfide 3.922 (Scheme 3.133) [411]. The starting sulfide 3.922 was synthesized by treatment of the mono-trisopropylsilyl-protected orf o-diethynylbenzene 3.921 with butyllithium excess followed by the addition of sulfur dichloride [411]. Cyclization of compound 3.922 (benzene, 200°C, 6 M of 1,4-cyclohexadiene) gave butyl-2-naphthylsulfide 3.923 in 53% yield. Comparison of the parameters of this reaction with the cyclization of ortho-diethynylbenzene showed that the presence of the sulfur atom increases the cyclization barrier although the yield from compound 3.922 is much less than that from ort/ o-diethynylbenzene. These studies are consistent... 

Scheme 3.133 Synthesis and Bergman cyclization for butylthio-o-diethynylbenzene sulfide 3.922.

The above has shown that ethynylsulfides can undergo Bergman cycloaromatization to form one or two fused rings. In this way, dinaphtho[2,l- l, 2 -d]thiophene 3.931 can be obtained together with dinaphthyl sulfide 3.930 in a cascade of cyclizations starting with bis(o-diethynylbenzene)sulfide 3.929 (Scheme 3.135) [411]. At low concentrations of 1,4-cyclohexadiene, the yield of 3.931 increases. Development... 

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