ipso-Nitrodesilylation or Nitrodegermylation of Vinylsilanes and Vinylgermanes by Nitrate Salts

We present a simple, additive-free protocol for the ipso-nitrodesilylation of vinylsilanes (Csp2-SiR3 to Csp2-NO2) with nitrate salts to form trans-nitroalkenes, mostly applicable to β-styrylsilanes. For β-alkyl-substituted vinylsilanes, the nitration yields are low. A series of metal nitrate salts are suitable, with the optimum nitrating agent being Fe(NO3)3 nonahydrate in acetonitrile. One oxygen atom from nitrate is connected to silicon, as the fate of the silyl group is its transformation into a silanol. Our mechanistic analysis is consonant with a polar mechanism involving a carbocationic intermediate stabilized by the β-silicon effect, which can result either from the rearrangement of a hypervalent silicon species formed by the nucleophilic attack of a nitrate ion on the silicon, or by the electrophilic substitution on the alkene double bond by the NO2+ moiety from metal nitrate. The ipso-nitrodegermylation of the analogous β-aryl-substituted vinyltrimethylgermanes appears also to be feasible in good to moderate yields.