Triisopropylsilylethynyl triflone

Vasu Nair Byung I. Seo University of Georgia, Athens, GA, USA 

Alternate Name TIPS-acetylene triflone or TIPS-ethynyl triflone. Solubility most aprotic organic solvents. 

Form Supplied in colorless liquid not commercially available. Analysis of Reagent Purity reagent must be made fresh. Handling, Storage, and Precaution sensitive to free radical 

The TIPS variant in eq 1 is used not only neat on the cyclic C-H substrates THF, tetrahydrothiophene, and cyclohexane, but also in acetonitrile with adamantane, which substituted exclusively at the tertiary C-H (50% yield). Alkynylation was also successful with distal functionality, i.e. R = (CH2)20SiR3 and (CH2)3C1, but the triflone could not be formed with ether functionality closer to the acetylene. 

Previously, the alkynylation had heen reported with other attached hydrocarbon groups (R = Ph and / hexyl in eq 1). The presence of a second acetylene group in the hydrocarbon group R was successful only with four methylenes, but not fewer, separating the two acetylenes. However, with enough separation the outer acetylene succeeded with only H-substitution to yield 8 in eq 2 and the product could be carried through triflation and a second alkynylation to form 9. 

Alkylation of H2S with alkyl halides often leads to the formation of a mixture of alkanethiols, disulfides, and elimination products. But, when the hthium hydrosulfide was treated with TIPSCl (eq 24), the resulting triisopropylsilanethiol had one site blocked, allowing clean monoalkylation with a variety of electrophiles, including allyhc, benzylic, and 1° or 2° halides and tosylates (eq 25).  

Removal of the TIPS group with TBAF or CsF in the presence of H2O led to the formation of thiol. Unsymmetrical sulfides can be formed when a suitable alkylating agent was used to trap the thiolate intermediate after addition of the fluoride source (eq 26).  

TIPSCl reacted with 2-lithio-l,3-dithiane to form a precursor to formyltriisopropylsilane, which was unmasked in a two-step sequence (eq 27).  

Although formyltriisopropylsilane ignites in air, the hydrazone derivative was isolable and formyltriisopropylsilane was used in situ in Wittig and aldol reactions. 

Related Reagents. r-Butyldimethylchlorosilane f-butyldi-phenylchlorosilane triisopropylsilyl trifluoromethanesulfonate. 

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