Functionalisation of tetraalkylsilanes derived from CH activation; towards annulations of diterpenoids

Vinyl trialkylsilanes are efficient substrates for use in the ortho alkylation of aromatic ketones catalysed by zerovalent ruthenium complexes, giving, e.g. (2-trimethylsilylethyl)acetophenones. Methods for the selective desilylation–functionalisation of such tetraalkylsilanes are investigated. Some diterpenoid tetraalkylsilanes derived from the ruthenium-catalysed insertion of vinyltrimethylsilane have been functionalised by benzylic bromination of an ArCH2CH2SiMe3 fragment with NaBrO3–Na2S2O5 (optimally), leading to a 1,2-dibromoethyl derivative. Further transformations culminated in the overall conversion of ArCH2CH2SiMe3 into ArCOCH3. Attempted aldol coupling of the resulting 1,4-diketone provoked skeletal reorganisation. A tetraalkylsilane was converted into a silanol (ArCH2CH2SiMe2OH) by the action of aluminium chloride and water, but further oxidation of this silanol to the primary alcohol (ArCH2CH2OH) was unsuccessful.