[62418-65-9] · C11H22OSi · 3-Triethylsilyloxy-1,4-pentadiene · (MW 198.42)
Physical Data: bp 140 °C; n
Solubility: sol pentane, benzene, THF, ether, CH2Cl2.
Analysis of Reagent Purity: NMR, GC (4.56 min on 1 mm 5% OV 225 on Chromosorb W at 108 °C) or TLC: R
Form Supplied in: commercially available.
Preparative Methods: by silylation of 3-hydroxy-1,4-pentadiene with Chlorotriethylsilane.1,2 Other relatives of the title compound are available by silylation with Chlorotrimethylsilane2 or t-Butyldimethylchlorosilane.3 3-Trimethylsilyloxy-1,4-pentadiene is usually prepared and used in situ. Storage of 3-trimethylsilyl-1,4-pentadiene at -30 °C is recommended.2 The dianion of the parent 3-hydroxy-1,4-pentadiene can also be prepared.4
Handling, Storage, and Precautions: use in a fume hood.
3-Triethylsilyloxy-1,4-pentadiene may be used to prepare the useful 3-triethylsilyloxypentadienyl anion via metalation with s-Butyllithium (eq 1).1,2
Reaction of the 3-triethylsilyloxypentadienyl anion with electrophiles is usually regioselective for the g-adduct (eq 2 and Table 1).2,5,7 This reaction provides a direct route to substituted dienes, as well as to vinyl ketones after hydrolysis. A representative procedure is as follows: a solution of 3-triethylsiloxy-1,4-pentadiene in THF was cooled to -78 °C and a solution of s-butyllithium in cyclohexane (1.1 equiv) was added dropwise over 30 min. The electrophile dissolved in THF was then added dropwise to the often yellow pentadienyl anion solution. The reaction mixture was stirred for 15 min and then quenched with saturated NH4Cl solution and the product extracted with ether.
A wide variety of electrophiles may be used and the selectivity is based on kinetics. In some cases the products have been thermally interconverted (cf. entry 8, Table 1).5,6 Because of polarity differences, the isomeric products usually can be separated by silica gel chromatography.
Elaboration of the alkylation products to give vinyl ketones may be accomplished with Potassium Fluoride in methanol at -10 to 0 °C or in i-PrOH at 25 °C (eq 3). For example, preparation of b-hydroxylethyl vinyl ketone synthons has been accomplished using a PhMe2Si unit as a masked hydroxyl group (eq 3).7,8
The method has been used to prepare intermediates for intramolecular Diels-Alder reactions (eqs 4 and 5).2-6 The title reagent may provide ether the diene for the intramolecular Diels-Alder (eq 4)4 or, after hydrolysis, the dienophile (eq 5).3
Stephen R. Wilson
New York University, NY, USA