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 i ntermediates for the preparation of a variety of functionalised allyls ilanes. These allylsilanes are interesting building blocks, used for e xample, 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 valua ble precursors to a range of useful heterosubstituted allyllithium rea gents. Finally, a one-step preparation of functionalised allylsilanes from readily available 3-methylseleno-2-[methylselenomethyl]propene is reported.