Exploration of new synthetic methods for aromatic compounds based on the benzyne cycloaddition reactions

点击翻译按钮获取中文摘要

Some new methods for aromatic synthesis have been developed by utilizing the benzocyclobutene derivatives obtained by the regioselective cycloaddition of benzyne which we previously reported.(1) Novel synthesis of isochroman-3-one :Upon treatment with an aromatic aldehyde and lithium tetramethylpiperidide, a benzocyclobutenone undergoes insertion of its C( 1 )-C(4) bond into the carbonyl of the aldehyde to give isochroman-3-one derivative. The reaction proceeds under mild conditions, and is applicable to various combinations of benzocyclobutenone and aromatic aldehyde, thereby enabling to synthesize the derivatives with an alkyl or an alkoxy substituent at the C(4) which were difficult to synthesize by the methods so far reported.(2) Ring expansion of 2-alkoxy-2-vinylbenzocyclobutenol into substituted naphthalene :Promoted by lithium dialkylamide, 2-alkoxy-2-vinylbenzocyclobutenol derivatives undergo ring expansion by incorporating the two vinyl carbons between the C(1) and C(2) positions of the fourmembered ring. The reaction proceeds stereoselectively, and the stereochemical courses give new views into the reaction mechanism.(3) Novel synthesis of biaryl compounds :The cyclobutenolate generated by addition of aryllithium to 2-alkoxy-2-vinylbenzocyclobutenone gives aryl-substituted dihydronaphthalene via the ring expansion. Aromatization of the product is effected under mild acid treatment to give the corresponding 1-arylnaphthalene. The method is valid for the synthesis of the derivatives which are sterically congested around the biaryl linkage.