[70901-64-3] · C8H16Si · 2-Trimethylsilylmethyl-1,3-butadiene · (MW 140.33)
Physical Data: bp 69-70 °C/80 mmHg.
Analysis of Reagent Purity: 1H NMR.
Purification: by distillation.
Solubility: sol common organic solvents.
Preparative Methods: prepared most conveniently by the coupling reaction of the Grignard reagent prepared from (Chloromethyl)trimethylsilane with 2-chloro-1,3-butadiene (chloroprene) in the presence of a catalytic amount of Ni[Ph2P(CH2)3PPh2]Cl2 (91% yield) (eq 1).2 Alternatively, it can be prepared by the reaction of the same Grignard reagent with allenylmethyl phosphate in 57-73% yield (eq 2).3 Direct metalation of Isoprene followed by the reaction with Chlorotrimethylsilane gives 2-trimethylsilylmethyl-1,3-butadiene in low yield.4 Thermal isomerization of 1-trimethylsilylmethylcyclobutene to 2-trimethylsilylmethyl-1,3-butadiene has also been reported.5
Handling, Storage, and Precautions: can be stored in a glass bottle under nitrogen.
Like other allylic silanes, 2-trimethylsilylmethyl-1,3-butadiene reacts with various electrophilic species such as acetals, acid chlorides, and carbonyl compounds with the aid of a Lewis acid to give the corresponding isoprenylated compounds (eqs 3-6).
The direct reaction of 2-trimethylsilylmethyl-1,3-butadiene with isovaleraldehyde gives (±)-ipsenol (2-methyl-6-methylene-7-octen-4-ol) in rather low yield (30%) (eq 5). However, ipsenol is obtained in 62% overall yield by the reaction of 2-trimethylsilylmethyl-1,3-butadiene with isovaleryl chloride, followed by reduction with Diisobutylaluminum Hydride (eq 7). Similarly, (±)-ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) is obtained by reduction of myrcenone, prepared by the reaction of 2-trimethylsilylmethyl-1,3-butadiene with 3,3-dimethylacryloyl chloride, in 75% overall yield (eq 8).
The methyl ether of ipsenol can be prepared by the reaction of 2-trimethylsilylmethyl-1,3-butadiene and isovaleraldehyde dimethyl acetal with Iodotrimethylsilane catalysis (90%) (eq 9)6 and from methyl 1-chloro-3-methylbutyl ether (72%).7 Isoprenylation of carbonyl compounds with 2-trimethylsilylmethyl-1,3-butadiene initiated by a catalytic amount of Tetra-n-butylammonium Fluoride (TBAF) (eq 10) is the most convenient route to ipsenol and ipsdienol.8 Reactions with g-vinylbutyrolactone9 and N-alkylmethyleneiminium salt10 are also reported.
2-Trimethylsilylmethyl-1,2-butadiene and 2-Trimethylstannylmethyl-1,3-butadiene undergo facile cycloaddition with dienophiles (eq 11). The reactions of 2-trimethylsilylmethyl- and 2-trimethylstannylmethyl-1,3-butadiene with unsymmetrical dienophiles give the so-called para product predominantly, and the selectivity is much higher in the reactions with 2-trimethylsilylmethyl- and 2-trimethylstannylmethyl-1,3-butadiene compared to reactions with isoprene. The para/meta ratios in the reactions with Methyl Acrylate (eq 12) are: 70/30 (X = H), 84/16 (X = SiMe3), and 91/9 (X = SnMe3).11
2-Trimethylsilylmethyl-1,3-butadiene undergoes highly regioselective Aluminum Chloride-catalyzed Diels-Alder reactions with dienophiles such as Acrolein and Methyl Vinyl Ketone in which the
para isomers are obtained almost exclusively (eqs 13 and 14). The adducts are converted readily to a variety of naturally occurring mono- and sesquiterpenes (eq 15).12
2-Trimethylsilylmethyl-1,3-butadiene forms a titanium(III) complex by the reaction with Dichlorobis(cyclopentadienyl)titanium and n-PrMgBr. The complex reacts with carboxylic acid chlorides RCOCl (R = alkyl, alkenyl) to give b,g-unsaturated ketones (eq 16).13
The regioselectivity of nucleophilic additions to the Co(CO)3BF4 complex has also been examined.14 Ziegler-Natta polymerization of 2-trimethylsilylmethyl-1,3-butadiene catalyzed by Triethylaluminum and Titanium(IV) Chloride gives predominantly cis-1,4-polymer. However, anionic polymerization yields a polymer whose microstructure is composed of cis-1,4-, trans-1,4-, and 3,4-units.15
Tohoku University, Sendai, Japan