Preparation and synthetic utility of 2-methylselenomethyl allyl methyl selenide. A valuable precursor to 2-silylmethylallyllithiums

3-Lithio-2-[silylmethyl]propenes, easily prepared from 3-methylseleno-2-[silylmethyl]propenes by the cleavage of the C-Se bond, are useful intermediates for the preparation of a variety of functionalised allylsilanes. These allylsilanes are interesting building blocks, used for example, as annelating agents in the efficient synthesis of spiroketals by the Intramolecular Silyl-Modified Sakurai (ISMS) cyclisation. The methodology described in this article provides also an expedient route to a range of heterosubstituted methylselenopropenes, which are valuable precursors to a range of useful heterosubstituted allyllithium reagents. Finally, a one-step preparation of functionalised allylsilanes from readily available 3-methylseleno-2-[methylselenomethyl]propene is reported.