Trimethylsilyloxy vinyllithium

Preparative Methods hromine-lithium exchange starting from (Z)-2-hromo-l-(trimethylsilyloxy)ethylene in dry Et20 

Handling, Storage, and Precautions when prepared with 2 equiv of r-BuLi the reagent is stable in Et20 over 20 h at —70°C 1 from —60°C it begins to decompose with formation of acetylene.  

General Discussion. (Z)-(Trimethylsilyloxy)vinyllithium (1) has essentially been used for a one-pot vinylogation of carbonyl compounds. Condensation of (1) with aldehydes and ketones (2) occurs readily at low temperature (—70 °C) then treatment of the reaction mixture with an acidic solution in mild conditions (IN hydrochloric acid, 0 °C to rt) produces the Q ,/3-unsaturated aldehydes (3), without double bond migration. The ( 0 isomers are obtained alone (from aldehydic compounds) or very predominantly (fromketonic compounds). The intermediate adducts, y-hydroxy enol ethers (4), can be isolated by slightly basic mild hydrolysis (eq l).l 

Thus (Z)-(trimethylsilyloxy)vinyllithium (1) is an excellent reagent for the preparation of building blocks such as (4), (5a), and (5b) (eq 3), which are useful for short convergent syntheses of terpenoid compounds (eqs 4 and 5).  

Condensation of acetylacetaldehyde dimethyl acetal with reagent (1) leads to the 5-aldolacetal (3c) in 90% yield, which has been transformed by classical methods into bromoacetal (4) and bromo enol ethers (5a,5b) (eq 3).  

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Trimethylsilyloxy)vinyllithium 548 has been prepared by tin-lithium exchange from the vinylstannane 552, which is generated from acetyltri-n-butyltin 551 (Scheme 149)830. This vinyllithium suffers a reverse Brook rearrangement to generate the alkoxide 553 used for the synthesis of acylsilanes831. 

Z)-2-Bromo-l-(trimethylsilyloxy)ethylene 1 is used essentially as a precursor of (Z)-2-(trimethylsilyloxy)vinyllithium (eq 1).3... 

M) and r-Butyllithium at —70 °C under inert atmosphere. One equivalent of t-BuLi is sufficient if (Z)-(trimethylsilyloxy)-vinyllithium is condensed with reactive electrophilic reagents which are added 10-20 min after the end of the addition of r-BuLi. In other cases, two equivalents of f-BuLi are needed, the second equivalent is used to destroy f-BuBr formed during the exchange and the electrophilic reagents are added after the end of addition of f-BuLi. 

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