4-Bromo-benzocyclobutene

During the workup of the o-xylene oxidation run, a strong lachrymator made its presence felt. This was probably a-bromo-o-xylene, although it was not detected in the low voltage mass spectrum. We suspected that a strong peak at mass 104, undoubtedly caused chiefly by a fragment ion derived from o-methylbenzyl alcohol by loss of H20 (I), might also contain a contribution from benzocyclobutene from the interaction of a-bromo-o-xylene with the indium tube used to introduce samples into the spectrometer. To test this possibility, benzyl bromide and a-bromo-o-xylene were run separately under the same conditions. 

Intramolecular cyclizations via aryl anions have been used to prepare benzocyclobutenes (138) from o-bromo-3-phenethyl bromides and benzocyclobutenols (139) from o-bromostyrene oxides. ... 

The sonochemical conditions minimize p-elimination.274 Perfluoroalkylation of arene tricarbonyl-chromium aldehydes occurs without decomposition of the transition metal group used to induce stereoselectivity in the addition.275 l,l/l-Trifluoro-2-bromo-2-propene adds to an aldehyde function in the presence of zinc and copper chloride (Eq. 62).276 The adduct was used for the s3mthesis of steroid precursors via a ring opening of the benzocyclobutene to an ortho quino-dimethane, followed by an intramolecular Diels-Alder reaction. 

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