Benzocyclobutene-1,2-diones

With substituted benzocyclobutene-1.2-diones other derivatives are available.36 Radical intermediates seem to be involved in the reaction process.37... 

The diazotization of anthranilic acid, a classic route to benzyne, when carried out in the presence of vinyl acetate, vinyl ethers or 1,1-dichloroethylene gives the expected benzocyclobutenes in about 40% yield. Despite the rather moderate yields this method represents a convenient route to multigram quantities of the parent compounds, benzocyclobutenol and benzocyclobutenone. The latter is easily converted to benzocyclobutene-1,2-dione. The diazotization sequence applied to 2-amino-3,6-dimeth-oxybenzoic acid and 1,1-dichloroethylene results in a 80% yield of 3, imethoxycyclobuten-l-one. Trapping of benzynes with other ethylene derivatives, and especially more substituted alkenes, has given generally poorer, variable results. ... 

Switlak, K., He, D., and Yates, P, Intramolecular trapping of an oxacarbene intermediate in the photochemical ring expansion of a cyclopentanone,/. Chem. Soc., Perkin Trans. 1, 2579, 1992. Staab, H. A. and Ipaktschi, J., Photochemische reaktionen des benzocyclobuten-1, 2-dions, Chem. 

A benzocyclopropenone intermediate 177 may account for the formation of terphenic acid 178 on hydrolytic decomposition of benzocyclopropenium cation i 761303). Likewise, the intermediacy of benzocyclopropenone (166, R = H) is claimed from spectroscopic evidence in the low-temperature photolysis of benzocyclobutene dione leading to benzyne130b). 

Benzocyclobutene-l,2-dione (11) can be condensed with benzene-1.2-diamine to provide an annulated quinoxaline (cf. Houben-Weyl, Vol. E9b/Part 2, p203), which on oxidation with hydrogen peroxide in acetic acid leads to the 1,4-diazocine derivative 12.34... 

Abb. 10. Beziehungen zwischen dem Edukt Benzocyclobuten-3,4-dion (E) und sei-nem Photo- (Ti) und Thermo-Transienten (T2)... 

The highly strained benzocyclobutene-l,2-dione (24) forms dimers when irradiated in 2 1 pentane-methylene chloride63 or cyclohexane84 and forms adducts when irradiated in ethanol or in the presence of olefins. These products have been interpreted in terms of a carbene intermediate (25). 

Benzocyclobutene-l,2-dione (74) undergoes base-catalysed ring fission between the carbonyls to give 2-formy I benzoate (75). Rate constants, activation parameters, isotope effects, and substituent effects have been measured in water.107 Rapid reversible addition of hydroxide to one carbonyl is followed by intramolecular nucleophilic attack on die otiier, giving a resonance-stabilized carbanionic intermediate (76a)-o-(76b). 

Until now, only few attempts were made to apply the ortho photocycloaddition to organic synthesis. Particular interest lies in the field of compounds possessing interesting biological activity (Sch. 22). The cyclohexane-1,3-dione carboxylic acid derivative 110 can be used as core structure of new herbicides [27,51,84]. Benzocyclobutenes 75a,b obtained... 

The same sequence when applied to benzocyclobutene-l,2-diones such as (118) afforded the adduct (119 80%), which was rearranged upon heating at 160 °C and air oxidation to the anthraquinone... 

In contrast, for reaction of benzocyclobutene-l,2-diones (108) to give 2-sulfonylbenzoic acids (113) in water-DMSO, p — 3.6, = 1.7, and reaction... 

In the presence of pyridine, photolysis of benzocyclobutene-l,2-dione (196) leads to the formation of pyridine ylide (197), and this is thought to arise by reaction with bisketene formed from the substrate dione rather than from an oxacarbene (198). 3-(2-Hydroxy-4-methoxyphenyl)-4-phenyl-2(5H)-fura-none, one of the photoproducts of 6-methoxybenzofuran-2,3-dione and styrene, has now been synthesised. ... 

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