Silyl sulfides, hydrolysis

The TIPS group imparts a unique stability to silyl sulfides. They present a remarkable resistance toward hydrolysis. The TIPS group can be removed under mild conditions. Thus, treatment with CsF/DMF or TBAF/THF at room temperature followed by hydrolysis affords thiols. Alternatively, the intermediate thiolate can be alkylated in situ with an alkyl halide such as allyl bromide to provide the corresponding sulfide (eq 2). 

Enantioselective aldol reactions. Enders et ul. have reported a regiospecific and enantioselective aldol synthesis. The method involves conversion of a methyl ketone into the chiral hydrazone 2, a-metalation, reaction with a carbonyl compound, and silylation to form a doubly protected ketol 3. The chiral ketols 4 are obtained by oxidative hydrolysis with H2O2 (30%) at pH 7 or by sensitized photooxidation in THF followed by reduction with dimethyl sulfide. Optical yields are 30-60%. The absolute configuration of the ketols is not known at present. 

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