Reactions of Trimethylstannide and Trimethylsiliconide Anions with Aromatic and Heteroaromatic Substrates

AL POSTIGO, SANTIAGO E. VAILLARD, Y ROBERTO A. ROSSI

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

JOHN WILEY & SONS LTD

Año: 2002 vol. 12 p. 889 - 893

0894-3230

 A parallel study was carried out on the reactions of Me3Sn- and Me3Si- ions towards aromatic and heteroaromatic substrates in hexamethylphosphoramide (HMPA) as solvent. It was found that Me3Si- ions are more reactive and therefore less selective than Me3Sn- ions. In HMPA, PhI and PhBr react with Me3Sn- ions through an HME pathway. PhCl also reacts by an HME reaction, but under photostimulation the SRN1 mechanism competes with the HME process. With PhF as substrate, Me3Sn- ions afford (4-fluorophenyl)trimethylstannane, presumably through a hypervalent tin species. Under irradiation, the SRN1 mechanism operates concurrently with the formation of the hypervalent tin species. Me3Si- ions, on the other hand, react with PhX (X = Cl, Br, I) to yield the ipso substitution product, presumably through the intermediacy of a hypervalent silicon species. PhF affords, upon reaction with Me3Si- ions, o- and p-fluorotrimethylsilylbenzenes together with the ipso substitution product PhSiMe3. A novel type of nucleophilic substitution mechanism takes place with Me3Si- ions upon reaction with aromatic and heteroaromatic substrates without classical leaving groups in HMPA.