From benzynes

X-ray crystal structure, 6, 516 Benzophenanthridines synthesis from anils, 2, 416 Benzophenanthridines, tetrahydro-synthesis, 2, 469 Benzo[c]phenanthridines synthesis, 2, 414 from aryl isocyanides, 2, 411 from benzynes, 2, 432 Benzo[i]phenanthridines synthesis, 2, 414 Benzophenanthridinones... 

Pomerantz synthesis, 2, 429 synthesis, 2, 413 from benzynes, 2, 432 Isoquinoline, 1,2,3,4-tetrahydro-mass spectrometry... 

Another reaction which requires o-quinoneallides as intermediates is the synthesis of chromenes from benzyne and ,/3-unsaturated aldehydes (Scheme 5).189 The formation of the unstable benzoxete was confirmed by isotope labeling. Yields are in the range 4—40%. 

To confirm reaction scheme (4) for the formation of naphthalene and biphenyl, phthalic anhydride was allowed to react with benzene-dx (Fields and Meyerson, 1966c). Barring an appreciable isotope effect, two-thirds of the naphthalene should contain a deuterium atom and one-third only protium. Biphenyl arises in two ways insertion of benzyne into a C—H bond of benzene and pyrolysis of benzene. Biphenyl from benzyne insertion should form with retention of the deuterium atom biphenyl from benzene pyrolysis should—again ignoring any isotope effect—be d0, dlt and dz on the statistical basis of losing two, one, or zero deuterium atoms from a total of twelve protiums and deuteriums in the over-all reaction of two benzene molecules. The amount of biphenyl-... 

Benzyne in solution reacts as a dienophile Wittig (1957) first demonstrated this in the reaction of benzyne with furan. Corbett and Porter (1965) obtained further supporting evidence by isolating 1,4-addition products from benzyne with 1-vinylnaphthalene and 3-vinylbenzo[b]-thiophene Dilling (1966) did the same with styrene. 

Trimellitic anhydride yielded products derived both from benzyne and carboxybenzyne. Decarboxylation at 690° should be extensive, and this compound then would react like phthalic anhydride. Under the circumstances, the survival of appreciable amounts of carboxybenzyne derivatives was surprising. The 4-methyl ester of trimellitic anhydride would probably be a stable source of carboxybenzyne methyl ester. 

We propose rather that thiophyne is formed by intramolecular dehydrogenation, and that the minor pyrolysis products of thiophene arise from the reaction of thiophyne with thiophene (Scheme 22). Phenylthiophene is a major product from benzyne and thiophene, and therefore suggests the intervention of benzyne in thiophene pyrolysis. A likely source of benzyne in this system is the 1,4-addition of thiophyne to thiophene followed by loss of acetylene and sulfur (Scheme 23). Such a scheme parallels the behavior of benzene, which at 690° gives a small amount of naphthalene, arising presumably from intramolecular... 

Benzyne, generated either by oxidation of 1-aminobenzotriazole with lead tetraacetate or by decomposition of benzenediazonium-2-carboxylate, was efficiently trapped by (2) to give 88% of the 1,2-benzisoselenazole (26) however, it was trapped in only 5-10% yield by (1). The series of adducts analogous to (26), prepared from benzyne and substituted benzoselenadiazoles (81JCS(P1)607), occurred via attack of the benzyne at the selenium atom followed by reorganization of the intermediate according to Scheme 6. Benzyne addition to dimethylthiadiazole produced methyl derivatives of quinoline and 1,2-benzisothiazole (82CC299). 

The reaction of thiobenzophenones with benzyne shows the superiority of the present iodine precursor 2 over benzenediazonium-2-carboxylate (5), which is widely used.8 The reaction of the hypervalent iodine precursor 2 with thiobenzophenones affords [4+2] cycloadducts from benzyne and thiophenzophenones under mild... 

The direct synthesis of benzocyclopropene (1) from benzyne and a carbene or from synthetic equivalents thereof has not yet been realized, but arc-generated carbon reacted with benzene at — 196°C to give benzocyclopropene (1) in 11% yield, together with toluene (24%), cyclo-heptatriene (17%), 7-phenylcycloheptatriene (21%) and heptafulvene (17%). Phenylcarbene in an excited state is a possible intermediate in the formation of benzocyclopropene. ... 

Benzyne (145) may also be used as a starting material, thus dibenzotetraselenafulvalene (149) can be prepared starting from 1,2-bismethylselenobenzene (146), which is obtained from benzyne (145) and dimethyldiselenide and subsequent coupling of the resulting benzo-1,3-diselenole-2-thione (147) with triphenyl phosphite (Scheme 35) <84TL833>. 

Vinylbenzo[b]thiophen and benzyne (from o-bromofluorobenzene) afford 62 (13%) dehydrogenation of the 1 1 adduct 61 is possibly induced by attack of benzyne.60 Formation of the 1 1 adduct 45 (14%), from benzyne and l,3-diphenylbenzo[c]thiophen (143) is accompanied by some desulfurization to give 9,10-diphenylanthracene (9%)48 45 also loses sulfur at 250°C. 

N-phenylation. The further reaction of 87 and 88 with benzyne to give 9-aminoanthracene derivatives 91 (cf. the mechanism outlined in Scheme 12) is blocked by the presence of substituents at the bridgehead positions as in 86. Anthracene (9%) is also produced from the reaction of 87 with benzyne,48 and the formation of the tetramethyltriptycene 93 from benzyne and the isoindole 92 is attributed to a similar deamination of an intermediate anthracen-9,10-imine.68 Deamination of 86 and 87 is more conveniently accomplished by treatment with hydrogen peroxide.72... 

Benzoselenadiazole (128) behaves as a heterodiene toward dimethyl acetylenedicarboxylate, with which it gives the quinoxaline 124 and selenium. But 128 reacts differently with benzyne (generated from 4 or from 9) to give the 1,2-benzisoselenazole derivative 132 (88%) and a small amount of a cis,trans stereoisomer of 132.82 The analogous adduct 131 is obtained in lower yield from benzyne and 2,1,3-benzothiadiazole (127). The structure of these benzyne adducts is strikingly reminiscent of 135, which is obtained from a photochemical addition of dimethyl acetylenedicarboxylate to 126 via a nitrile oxide intermediate.84 However, for reasons given elsewhere,82 a nitrile selenide is unlikely to be an intermediate in the formation of 132, which is better explained by the mechanism outlined in Scheme 16. As in the case of thiophen (Section V,B), this is a 1,3-cycloaddition (in one or two steps) of benzyne to the heterocycle, enabled by the use of d orbitals on the sulfur or selenium atom. 

A series of adducts analogous to 132 has been prepared from benzyne and substituted 2,l,3-benzoselenadiazoles.84a The adduct 133, from 5,6-dimethyl-2,l,3-benzoselenadiazole (129), undergoes a further remarkable rearrangement either thermally or photochemically to give the selenocyanate 136. The corresponding compound 137 is obtained directly from the reaction of benzyne with 130, which implies that the adduct 134 is even more labile... 

Pacquer et al. also recognized a second series of intensely colored 1 1 adducts, the trithiapentalenes 153, from benzyne and 5-aryl-l,2-dithiole-3-thiones (151).93 Although very little of 153 (Ar = Ph) was obtained (< 1%), p-anisyl, p-tolyl, and p-chlorophenyl compounds were formed in higher yields. Unsuccessful attempts to achieve the conversion 152 - 153 render more likely an independent pathway for the formation of 153, e.g., one involving an initial 1,2-cycloaddition of benzyne to the exocyclic C=S bond of 151. Derivatives of the related l,2,4-dithiazole-3-thione system 160 and benzyne also afford two series of 1 1 adducts 161 and 162 corresponding to 152 and 153, respectively.93... 

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