Synthesis and electrophilic substitution of some Hexa- and Penta-2,4-dienyl-silanes,-germanes and -stannanes

Penta-2,4-dienyl and hexa-2,4-dienyl derivatives of silicon, germanium and tin have been synthesized (normally as E/Z mixtures) by metalation of the corresponding pentadienyllithium reagents. The E/Z isomeric mixtures have been fully characterized by 1H and 13C nuclear magnetic resonance spectroscopy. Trifluoroacetolysis of these compounds (CF3COOD) has been studied by direct 2H n.m.r. spectroscopy, and ε-electrophilic attack is predominant. In contrast, sulfur dioxide insertion (with the stannanes) is γ-regiospecific, but these kinetic γ-sulfinates rearrange, by a presumed electrocyclic process, to the conjugated dienylmethylsulfinates.