P-Benzyne generation

Photoexciting 1,4-dibromobenzene in a molecular beam with 307-nm pump pulse photons leads to sequential loss of both bromine atoms within 100 fs the excited dibromide has a lifetime of 50 fs and the monobromide of 80 fs. The p-benzyne generated decays relatively slowly, showing a lifetime of 400 ps. It presumably leads to (Z)-3-hexene-l,5-diyne through a valence isomerization of the sort associated with the Bergman rearrangement. 

Jones, R. R., Bergman, R. G. p-Benzyne. Generation as an intermediate in a thermal isomerization reaction and trapping evidence for the... 

In a sequence of cycloaddition and cycloreversion, 3-phenyl-l, 2,4-triazine 1-oxides react with benzyne, generated from 2-aminobenzoic acid (see Houben-Weyl, Vol. 5/2 b, p 622 ff), to give 2-phenyl-l, 3-benzoxazepines in moderate yield.419... 

Okuma et al. <1998CL79, 2000BCJ155, 1999J(P 1)2997, 2005H(65)1553> published a series of papers describing reactions of various thioketones with benzyne generated from 2-trimethylsilylphenyl trifluoromethanesulfonate 96, phenyl[2-(trimethylsilyl)-phenyl]iodonium trifluoromethanesulfonate 97, or benzenediazonium-2-carboxylate 98, which led to the formation of benzothietes. Compounds 96-98 are good precursors of benzyne, but not in the... 

The Bergman and Breslow observations complement one another in that both ring-opened and ring-closed forms of p-benzyne can be generated. DPT calculations suggest that the closed form is 37 kcal/mol less stable than the open form and that the barrier to ring opening of the closed form is less than 6 kcal/mol which is not very different than the earlier MINDO 3 calculations. ... 

Benzynes, generated from 2-(trimethylsilyl)phenyl triflates, react with P-alkenyl-X(5)-phosphazenes via a formal r-insertion into the PN bond. A subsequent retro 2 - -2-cycloaddition/6 r electrocyclization-protonation cascade rationalizes the formation of the resulting 1,4-benzazaphosphorinium triflates (Scheme 21). 

Arynes and Derived Compounds.—The generation of tetiafluorobenzyne by thermal decomposition of the diazonium carboxylate (134), obtained by treatment of tetrafluoroanthranilic acid with n-butyl nitrite, was first reported some years ago, and Scheme 34 shows some recently described reactions of the benzyne generated in this way (see also p. 411 The reaction... 

Benzynes, generated from Kobayashi precursors (2-trimethylsilyl)-phenyl triflates), undergo 7i-insertion reactions into the P=N bond of N-aryl iminophosphoranes to afford, eventually, a-aminoaiyl-diphenyl-phosphine oxides (Scheme 3). ... 

Systematic studies by Popik and co-authors [240-249] led to two of the above methodologies for the photochemical generation of reactive enediynes and their derivatives capable of cycloaromatization into p-benzynes 3.488 or intermediates such as the naphthyl diradical 3.490 (Scheme 3.19) [249]. 

Benzyne itself has been isolated in solid argon at 8 K, and much evidence for the existence of arynes has come from trapping experiments and spectroscopy. Thus generation of benzyne (101) in the presence of furan (102) leads to the formation of the Diels-Alder (p. 197) adduct (103), which undergoes ready acid-catalysed... 

There has been a review of didehydropyridines, focusing on then formation from halopyridines and base.123 The reactions of tri-p-tolyloxonium salts with hydroxide in water yield a mixture of p- and m-cresols via a benzyne intermediate,124 as shown in Scheme 7. A benzyne intermediate, generated by loss of lithium fluoride, is also implicated in the reaction of organolithium reagents with fluoro-AyV-diallylanilincs leading to 3,4-disubstituted indolines.125 The reaction of benzyne with 1,8-diethynylnaphthalene has been shown to yield benzo [a]pyrene.126... 

The synthesis of the triptycene system illustrates a synthetic use of the important reactive intermediate benzyne (13) which is generated by the thermal decomposition of benzenediazonium-2-carboxylate (see Section 6.5.3, p. 900). The latter is produced when anthranilic acid (11) is treated with an alkyl nitrite in an aprotic solvent, and probably exists mainly as the zwitterionic form (12). 

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