| The tris(trimethylsilyl)silyl (sisyl) ether is photolabile, and possesses the potential to be used as a hydroxyl protecting group which can be photolytically cleaved selectively, in the presence of other silyl ethers. In order to compare its hydrolytic stability with that of a t-butyldimethylsilyl (TBS) ether, the rates of acidic hydrolysis of a series of sisyl and TBS ethers were determined under pseudo-first-order conditions. The sisyl ethers were found to be more hydrolytically stable in CDCl3 containing p-TsOH·H 2O, but less hydrolytically stable in a AcOH/THF/H2O solvent mixture.; The hydrolysis studies were extended to the corresponding series of alkoxyallyl- t-butylmethylsilanes, which were determined to be more hydrolytically stable than either the sisyl or the TBS ethers. The ability of the alkoxyallyl-t-butylmethylsilanes to function as both allylsilanes (undergoing silicon-carbon bond cleavage), and alkoxysilanes (undergoing silicon-oxygen bond cleavage), was examined under conditions that could lead to both processes. In the presence of Bronsted acids, silicon-oxygen bond cleavage occurred exclusively. Electrophilic substitution of the allyl group was only observed in the presence of the very sterically hindered triphenylcarbenium ion.; Allylsilanes were also originally envisioned as ideal nucleophilic partners for the development of a method of forming carbon-carbon bonds at the propargylic carbon atom of dicobalt-complexed acetylenic aldehydes or ketones, diastereoselectively. Allyl transfer onto racemic mixtures of chiral dicobalt pentacarbonyl(triarylphosphine)-complexed acetylenic aldehydes, leading to the formation of the hexa-1,5-enyne system, was accomplished with modest diastereoselectivity. |
