The Electrochemical Reductive Trimethylsilylation of Aryl Chlorides: A Good Route to Aryltrimethylsilanes and a Novel Route to Tris(trimethylsilyl)cyclohexadienes

Article abstract of DOI:10.1021/jo00043a031

The electroreductive trimethylsilylation of aryl chlorides R-C6H4Cl (R = H, o-Me, m-Me, p-Me) can be controlled so as to give, in good yields, either the corresponding aryltrimethylsilanes (products of the reduction of the carbon-chlorine bond) or mixtures of cis- and trans-tris(trimethylsilyl)cyclohexa-1,3(or 1,4)-dienes (products of the successive reduction of the carbon-chlorine bond and the partial reduction of the aromatic ring).Which of the two products is formed depends upon how much electricity is passed during the constant current electrolysis, in a one-compartment cell equipped with a sacrificial aluminum anode, of an aryl chloride in 80:20 THF/HMPA solution that also contains Et4NBF4 as the supporting electrolyte and excess Me3SiCl.The electroreductive trimethylsilylation of phenyltrimethylsilane gave, in 62percent yield, a mixture of three 3,5,6-tris(trimethylsilyl)cyclohexa-1,3-dienes, of which the trans, pseudo a-a isomer constituted 89percent.Such products cannot be obtained by the chemoreductive trimethylsilylation of phenyltrimethylsilane.The electroreductive trimethylsilylation of benzene and toluene produced the corresponding bis(trimethylsilyl)cyclohexa-1,4-dienes.The regio- and stereochemical outcomes of the electroreductive trimethylsilylation of the various substrates can be explained in terms of the electronic and steric effects of the substituents originally attached to the aromatic ring and the steric effects of the trimethylsilyl groups that are subsequently attached.