Benzyne trapping agents

Benzyne trapping agents 2,5-Di-p-anisyl-3,4-diphenylcyclopentadienone. 1,3-Diphenyl-isobenzofurane. Tetraphylcyclopentadienone. 

Benzyne trapping agents s. 19, 910 Benzotropolone-l, 2 -quinones from o-quinones via l, 2 -dihydroxybenzotropolones s. 18, 914 Pyrroles by 1,3-dipolar addition from acetylene derivatives... 

Naphthalenes from cyclones Benzyne trapping agents... 

In the context of this section it is important that Ruchardt and Tan (1970 a) found that (solid) benzenediazonium fluoroborate gave benzyne adducts with potassium acetate in the presence of aryne trapping agents such as tetracyclone or anthracene. This is, however, not the case if water is present (Cadogan, 1971). As a consequence of these observations, Cadogan et al. (1971) simplified the formation of arynes from diazonium ions by converting aniline or its substitution products into arynes in a... 

Mixtures of xanthone (246) and 3,4-benzocoumarin (247) result when 2-aryliodoniobenzoates 245 are heated at higher temperature. This reaction involves fragmentation of 245 to benzyne, carbon dioxide, and iodoarene. Thus, in the absence of trapping agents, the benzyne intermediate reacts with 245 to form cyclized products 246 and 247 (64JOC1637) (Scheme 63). 

Beazyae. Reactions of acetanilide in dry benzene with PCBN in the presence of tctraphenylcyclopentadienonc, anthracene, 9,10-dimethoxyanthracene, and methyl methacrylate a.s trapping agents give the corresponding benzyne adducts, 1,2,3,4-... 

This synthesis of 1,2,3,4-tetraphenylnaphthalene (7) demonstrates the transient existence of benzyne (5), a hydrocarbon that has not been isolated as such. The precursor, diphenyliodonium-2-carboxylate (4), is heated in an inert solvent to a temperature at which it decomposes to benzyne, iodobenzene, and carbon dioxide in the presence of tetraphenylcyclo-pentadienone (6) as trapping agent. The preparation of the precursor (4) illustrates oxidation of a derivative of iodobenzene to an iodonium salt (2) and the Friedel-Crafts-like reaction of the substance with benzene to form the diphenyliodonium salt (3). Neutralization with ammoniuim hydroxide then liberates the precursor, inner salt (4), which, when obtained by crystallization from water, is the monohydrate. 

Diphenyliodonium-2-carboxylate monohydrate. Mol, wt, 341,13, m.p, 220°, dec. This stable and safe reagent is useful for the generation of benzyne in an aprotic solvent in the presence of a reactive diene as trapping agent. The original preparative procedure has been improved to a point such that 2 g. of o-iodobenzoic acid (Aldrich, Eastman) can be converted into 2.1 g. of the benzyne precursor in li-2 hrs. working time. The synthesis of 1,2,3,4-tetraphenylnaphthalene can be... 

The efficiency of diphenylisobenzofurane as a trapping agent is demonstrated by its reaction with benzyne to produce the adduct (10) in 85% yield. The reagent... 

One of the simplest routes to benzyne starts with aniline which is converted to benzenediazonium ion. Benzyne is liberated when this ion is deprotonated by acetate base in solvents such as benzene, Eq. (20). Detracting from this approach, however, are competing reactions in which phenyl radicals and phenyl cations are formed. Presently it is possible to minimize the importance of radical chain side reactions and thereby to favor benzyne formation by adding a radical trapping agent such as 1,1-diphenylethylene. 8S ... 

Generation of benzyne (see also 1, 560). Campbell and Rees1 point out that the generation of benzyne from this precursor by oxidation with lead tetraacetate differs from other methods in that, in the absence of a trapping agent, the dimer, diphenylene, is formed in yields as high as 83%. The trimer, triphenylene, is formed in less than 0.5% yield. Addition reactions of benzyne generated in this way with 1,3-dienes have been discussed.2... 

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