7-(Phenylsulfonyl)-bicyclo[4.2.0]octa-1,3,5-triene as a synthetic intermediate.

7-(Phenylsulfonyl)-bicyclo[4.2.0]octa-1,3,5-triene as a synthetic intermediate.

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Title: 7-(Phenylsulfonyl)-bicyclo[4.2.0]octa-1,3,5-triene as a synthetic intermediate.
Author: Gowland, Barbara D.
Abstract: The role of 7-(phenylsulfonyl)-bicyclo[4.2.0]octa-1,3,5-triene (benzocyclobutene phenylsulfone (83)) as a synthetic intermediate is investigated. Attempts were made to prepare this compound by several new routes. Cyclization of 1-(chloromethyl),2-(phenylsulfonylmethyl)-benzene ( 127) was attempted with LDA, MeLi, and phase transfer conditions, as well as flash vacuum thermolysis. None of these modifications were successful. The synthesis of phenyl 2-(o-chlorophenyl)ethyl sulfone (80) was approached by a new route in moderate yields by condensation of the anion of methyl phenyl sulfone with o-chloro-benzyl bromide, followed by oxidation. Cyclization of (80) via a benzyne intermediate proved possible with only four equivalents of KNH2. Hindered bases such as 2,2,6,6-tetramethylpiperidide gave intractable tars. The o-quinodimethane intermediate of ( 83) could not be efficiently trapped with maleic anhydride; instead, adducts with toluene and anisole were obtained. A rationale is proposed for this transformation. The anion of (83) was found to be an efficient nucleophile, trapping alkyl bromides, iodides, ketones, and epoxides in high yields. Desulfonylations of the alkylated parent compound were carried out easily and in excellent yields to give the alkyl species. Thermolysis of 7-(phenylsulfonyl)-7-(5'-eta-hexenyl)-1bicyclo[4.2.6]octa-1,3,5-triene (161) resulted in 1,5 hydrogen abstraction to yield styrenes, whereas the desulfonylated species of (161) and (102) were transformed smoothly to tricyclic compounds. Novel approaches to 7-(hydroxy)-bicyclo[4.2.0]octa-1,3,5-triene (benzocyclobutenol (77)) were investigated by intramolecular attack of an aromatic halide on an epoxide via the Grignard or halogen-metal exchange. These attempts did not lead to the desired compound, but instead, gave bromohydrins and olefins.
Date: 1978
URI: http://hdl.handle.net/10393/10842

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