Propargylsilanes synthesis

Schmitt A, Reissig H-U (2000) On the stereoselectivity of y-lactol substitutions with allyl-and propargylsilanes - synthesis of disubstituted tetrahydrofuran derivatives. Eur J Org Chem 3893-3901... 

Allylsilane and Propargylsilane Synthesis. (lodomethyl)-trimethylsilane has been used to prepare aflylsUanes, which are t)q)icafly utilized in Lewis acid or fluoride ion-promoted reactions with carbonyl compounds to provide homoallylic alcohols. Treatment of Mc3SiCH2l with methyltriphenylphosphonium bromide and base produces an intermediate phosphonium salt which can be further utilized to prepare allylsilanes from carbonyl compounds. This procedure has been modified so that this series of transformations can be done as a one-pot procedure (eq 1). ... 

Scheme 4.52 Asymmetric synthesis of allenes via the allenyl- or propargylsilanes.

Polyene cyclization in terpene and steroid synthesis is critically dependent on the terminator in order to generate useful functionalities for further modification of the products. Allyl- and propargylsilanes have proven their value in facilitation of the cyclization and generation of an exocyclic methylene and allene, respectively. Thus, a concise approach to albicanyl acetate [126] and the rapid construction of a tetracyclic precursor of steroids [127] are sufficient to demonstrate the concept. Again, a comparison of the substrates with a silyl group with those having a simple alkyl moiety is very enlightening. 

A particularly interesting cyclization utilizes a propargylsilane group as a terminator for a biomimctic synthesis of a tetracyclic hydrocarbon (6) with a potential cortical side chain.5... 

A synthesis of the Inhoffen-Lythgoe diol (46.7, Scheme 2.46), a useful intermediate in the synthesis of Vitamin D derivatives, demonstrates the use of a chiral acetal in an asymmetric tandem cyclisation reaction.102 Once again, Lewis acid co-ordination to the less hindered oxygen of the acetal 46.1 initiated a Prins-like cyclisation that terminated by attack of the propargylsilane on an incipient tertiary carbocation. After removal of the chiral auxiliary, the allene function in the alcohol 46.4 was transformed into the side chain of 46.7 with the creation of two new stereogenic centres. 

The palladium/PPFA-catalyzed asymmetric cross-coupling of a-(trimethylsilyl)-benzylmagnesium bromide 25 has also been applied to the synthesis of optically active propargylsilane 29 (18% ee) by the use of l-bromo-2-phenylacetylene as a coupling partner (Scheme 2-18) [37]. 

Synthesis of Propargy Isilanes. A propargylsilane with a bulky group on silicon has been prepared in 34% yield from reaction of the Grignard reagent derived from propargyl bromide with TDSOTf (eq 21). Less reactive TBDMSCl did not react with... 

The synthesis of propargylsilanes has also been thoroughly explored, and these useful reagents are readily prepared by the addition of substituted lithioacetylides to Me3SiCH2l. Propargylsilanes have subsequently been used in titanium(IV) chloride-promoted reactions with acetals to yield functionalized Q -allenylsilanes or functionalized alkenes. 

Scheme 3-108. Cyclobutene synthesis using propargylsilanes and a,ji-unsaturated ketones.

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