Concise synthesis of functionalized benzocyclobutenones
作者:P.-H. Chen、Nikolas A. Savage、Guangbin Dong
DOI:10.1016/j.tet.2014.03.080
日期:2014.7
to access functionalized benzocyclobutenones from 3-halophenol derivatives is described. This modified synthesis employs a [2+2] cycloaddition between benzynes generated from dehydrohalogenation of aryl halides using LiTMP and acetaldehyde enolate generated from n-BuLi and THF, followed by oxidation of the benzocyclobutenol intermediates to provide benzocyclobutenones. The [2+2] reaction can be run on
derivatives with α-alkyl α-diazo esters utilizing a chiral scandium(III) N,N′-dioxide as the Lewis acid catalyst. This reaction supplies a highly chemo-, regio-, and enantioselective pathway for the synthesis of optically active β-keto esters with an all-carbon quaternary center through highly selective alkyl-group migration of the ketones. Moreover, the ring expansion of cyclicketones was accomplished under
Rapid, convergent, and regioselective synthesis of anthracenes
作者:John J. Fitzgerald、Neville E. Drysdale、R. A. Olofson
DOI:10.1021/jo00052a027
日期:1992.12
Anthracenes are obtained in moderate to good yield by the simultaneous treatment of benzocyclobutenols and halobenzenes with LTMP in tetrahydropyran. In the key step of this one-pot process, o-toluoyl anion intermediates from the known ring-opening of benzocyclobutenoxides add to halobenzene derived arynes. Methoxy-substituted benzocyclobutenols which are readily made regiospecifically by known methods also react regiospecifically with the single benzyne generated from either a 2- or 3-haloanisole. For example, the only trimethoxyanthracene isolated (48% yield) from the reaction of 6-methoxybenzocyclobutenol (8) with 5-chloro-1,3-dimethoxybenzene is the 1,3,8-isomer 20. When 1,2-dihydrocyclobuta[l]phenanthren-1-ol (14) and/or halonaphthalenes are the reactants, benzannulated anthracenes are formed; e.g., tribenz[a,c,h]anthracene in 68% yield from 14 and bromonaphthalene. In another extension, pentaphene (31) was made in one pot from o-dichlorobenzene.