[55339-31-6] · C5H11LiSi · (E)-2-(Trimethylsilyl)vinyllithium · (MW 106.19)
(for introduction of the b-(trimethylsilyl)vinyl moiety; the resulting alkenylsilanes undergo useful electrophilic substitutions of the TMS group1)
Form Supplied in: not available commercially; prepared in situ in either THF or diethyl ether.
Preparative Methods: attempts to produce synthetically useful quantities of (E)-2-(trimethylsilyl)vinyllithium (1) by reaction of Lithium metal with (2-Bromovinyl)trimethylsilane (2) failed because of concomitant metalation-elimination processes involving (1) and (2).2 However, the transmetalation process between (2) and excess t-Butyllithium has been effectively used to provide (1) (eq 1).3 An alternative route to (1) employs the transmetalation of a 1-(trimethylsilyl)-2-stannylethylene with organolithium reagents (eqs 2 and 3).4,5
Handling, Storage, and Precautions: must be prepared and transferred under inert gas (Ar, N2) to exclude oxygen and moisture.
Alkylating agents containing primary alkyl or methyl groups react with (1) in synthetically useful yields (eqs 4 and 5).4,5 Reaction of (1) with 1,2-Dibromoethane affords (2),4 while the use of metal or metalloidal halides generally results in high yields of coupling products (eqs 6-9).4 -7
An important subset of the reaction with metal halides is the conversion of (1) into more discriminating reagents. Thus the reaction of (1) with Copper(I) Iodide forms a diorganocuprate (3) which adds in a 1,4-fashion to conjugated enones (eqs 10 and 11).3a,b,8 In this same vein, (2) was transformed into an alkenylzinc reagent which displayed selectivity between adjacent aldehyde and ester functionalities (eq 12).9
The behavior of (1) with carbonyl-containing compounds is completely straightforward, with aldehydes (eqs 13 and 14),10,11 ketones (eqs 15 and 16),12,13 and Carbon Dioxide (eq 17)4 leading cleanly to expected products. Sato and co-workers have observed (1) to display considerable chemoselectivity in favor of an aldehyde functionality when presented with an ester as the alternative (eq 18).13
Robert F. Cunico
Northern Illinois University, DeKalb, IL, USA