Reactive intermediates. Part II. Some addition reactions of benzyne

Abstract

Benzyne, generated by the oxidation of 1 -aminobenzotriazole with lead tetra-acetate, adds to 1.3-dienes and reacts with nucleophiles in moderate to excellent yields, However, it generally dimerises much faster than it adds to heterocyclic dienes. Addition of benzyne to 2-methyl-and 2-benzyl-benzotriazole gives 1 -phenylbenzotriazole. Mechanisms for these reactions are proposed. Benzyne, generated oxidatively, does not add appreciably to mono-olefins.

Reactivity of Dehydrometallophthalocyanines and ‐porphyrazines

“…The conditions for the formation of biphenylene by dimerization of benzyne generated from 1-amino-benzotriazole were described by Campbell and Rees. [6] Thus, mixing solutions of PbA C H T U N G T R E N N U N G (OAc) 4 and 1-amino-benzotriazole in benzene or CH 2 Cl 2 at room temperature gave excellent yields (up to 82 %) of biphenylene; no adducts with solvents were mentioned. [6] As described above, 1 cannot be oxidized in either solvent, since a noticeable oxidation of Pc macrocycle occurs under these conditions.…”

“…An explanation for this could be given as follows: a nearly saturated solution of 8 in benzene has a one order of magnitude lower concentration than the one applied by Campbell and Rees in their experiments with 1N-amino-benzotriazole. [6] A tenfold decrease of the concentration of 8 would reduce the dimerization rate by 100 in case if the dimerization of dehydrobenzene follows the second order rate, which would allow the competitive reactions to dominate.…”

“…UV/Vis spectroscopy: Shimadzu UV-365. 1 (1), [2] bis(4-tert-butylphenyl)fumaronitrile (A), [15] 5,6-dicyano-1H-benzotriazole (B), [9] and 1-aminobenzotriazole (15) [6] were prepared as described earlier. Other chemicals and solvents were purchased from commercial sources and were used without additional purification, unless mentioned.…”

Recent Progress in the Synthesis of 2,3-Dihydrobenzofurans

“…48 In particular, Rees and Campbell highlighted that 1-aminobenzotriazole rapidly disintegrates in the presence of oxidants such as N-bromosuccinimide (NBS) or Pb(OAc) 4 to afford the corresponding benzyne under mild conditions and in stark contrast with base-induced eliminations. 49 Based on this work, Knight and co-workers more recently reported the use of a class of 7-substitued-1-aminobenzotriazoles for the synthesis of 2,3-dihydrobenzofurans. In particular, the exposure of compounds 27a-c, derived from the Boc-triazole 26 after a first treatment with an aldehyde in presence of n-BuLi and tetramethylethylendiamine (TMEDA) followed by deprotection of the Boc protecting group by trifluoroacetic acid in dichloromethane, to 2.0 equivalents of NBS in dichloromethane at room temperature leads to the formation of the corresponding benzyne intermediates, which rapidly undergo intramolecular trapping by the hydroxyl function to give the corresponding 2-alkyl-7-bromo-2,3-dihydrobenzofurans 28a-c (Scheme 19).…”

O ressurgimento da química de benzino com sililaril triflatos no contexto das reações de inserção em ligações sigma

“…[1][2][3][4][5][6] No entanto, vale destacar que os métodos tradicionais para geração de arinos, embora em posição de destaque no contexto da química de benzino, 1 inviabilizavam muitas das aplicações de tais espécies reativas no universo da química orgânica, devido às condições reacionais drásticas utilizadas, incluindo altas temperaturas, reagentes extremamente básicos ou fortemente oxidantes. [1][2][3][4][5][6] Em virtude do cenário delineado, Kobayashi e colaboradores publicaram no início da década de 80, uma rota sintética para a obtenção de 2-(trimetilsilil)fenil triflato (2), que foi usado na formação de benzino (1) sob condições reacionais brandas, que envolvem o uso de uma fonte de íons fluoreto, um solvente polar aprótico e temperaturas próximas da temperatura ambiente 7 (Esquema 1).…”