[22430-47-3] · C10H22Si2 · (1E,3E)-1,4-Bis(trimethylsilyl)-1,3-butadiene · (MW 198.45)
(building block for the stereodefined construction of conjugated polyenyl chains1-4)
Physical Data: bp 46-49 °C/15 mmHg; n
Analysis of Reagent Purity: GC/MS, IR, 1H and 13C NMR.
Preparative Methods: coupling of the Grignard reagent derived from (E)-2-(trimethylsilyl)-1-bromoethylene with the same bromo derivative leads to the silyldiene in 51% yield;5 a higher yield (62%) is obtained by reaction of bis(trimethylsilyl)methyllithium with (E)-3-(trimethylsilyl)-2-propenal.6 Other procedures involve the Pd0-catalyzed demercuration of bis[(E)-(2-trimethylsilylvinyl)]mercury, prepared from (E)-2-(trimethylsilyl)-1-lithioethylene and HgCl2 (77% yield),7 or the reaction of (E)-1,4-bis(trimethylsilyl)-2-butene with n-BuLi and TMEDA and subsequent oxidation with HgCl2 of the isolated bis-lithiated species, stabilized by complexation with TMEDA (57% yield).8
Handling, Storage, and Precautions: conveniently stored at -15 °C for several months, without appreciable isomerization.
A highly selective substitution of a trimethylsilyl group is readily performed with acyl chlorides in the presence of Aluminum Chloride to obtain silylated ketones with high retention of configuration (>98%). Dicarbonyl compounds are prepared with a one-pot procedure, by simply adding the second acyl chloride after completion of the first step, without isolation of the monosubstitution product (eq 1).1
The versatility of this approach is illustrated by the synthesis of polyunsaturated fatty acids of special interest. Ostopanic acid, a cytotoxic fatty acid,9 is directly obtained by acylation reactions with the appropriate acyl chlorides,2 whereas b-parinaric acid methyl ester, an interesting fluorescent probe for biological membranes,10 is prepared by a selective double acylation, followed by reduction and dehydration reactions (eq 2).3
Moreover, unsaturated keto silanes and diketones obtained according to eq 1 can be easily reduced to saturated keto silanes or 1,6-dicarbonyl compounds;11 unsaturated keto silanes can be transformed into enantiomerically enriched hydroxy derivatives by reduction and enzymatic kinetic resolution.12 Monosilylated unsaturated sulfides, precursors of a variety of dienylsilanes,13 can be also obtained by chemoselective electrophilic substitutions.4
Bromine addition leads to a tetrabromo derivative which can be bromodesilylated to (1Z,3Z)-1,4-dibromobutadiene (eq 3).14
Diels-Alder reactions with Maleic Anhydride (eq 4)5,6 lead to cyclic allylsilanes, which can undergo further interesting elaborations.6