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Tandem 1,4-Addition Reactions with Benzene and Alkylated Benzenes Promoted by Pentaammineosmium(II)

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journal contribution
posted on 11.10.2002, 00:00 by Fei Ding, Michael E. Kopach, Michal Sabat, W. Dean Harman
Electrophiles such as dimethoxymethane and 3-penten-2-one react with the complex [Os(NH3)52-benzene)]2+ in the presence of triflic acid to form metastable benzenium intermediates. These benzenium intermediates further react with carbon nucleophiles including silyl ketene acetals, (silyloxy)alkenes, and phenyllithium in an overall tandem 1,4-addition sequence. The metal fragment controls the relative stereo- and regiochemistry for both electrophilic and nucleophilic addition steps. Upon oxidative demetalation with silver triflate, cis-1,4 cyclohexadienes are formed in yields ranging from 16 to 82%. This methodology can also be used to dearomatize toluene and ortho- and meta-xylene with unexpectedly high regio- and stereocontrol.