Triethylsilyloxy-1,4-pentadiene

Charles G. Caldwell Merck Research Laboratories, Rahway, NJ, USA 

Preparative Method by sUylation of 3-hydroxy-1,4-pentadiene with chlorotriethylsilane. Other relatives of the title compound are avaUahle hy sUylation with chlorotrimethyl-silane or t-hutyldimethylchlorosUane 3-TrimethylsUyloxy-1,4-pentadiene is usuaUy prepared and used in situ. Storage of 3-trimethylsUyl-l,4-pentadiene at —30 °C is recommended. The dianion of the parent 3-hydroxy-1,4-pentadiene can also he prepared.  

A wide variety of electrophiles may he used and the selectivity is based on kinetics. In some cases the products have heen thermally interconverted (cf. entry 8, Table 1). Because of polarity differences, the isomeric products usuaUy can he separated hy sUica gel chromatography. 

Elaboration of the alkylation products to give vinyl ketones may be accomphshed with potassium fluoride in methanol at —10 to 0 °C or in i-PrOH at 25 °C (eq 3). For example, preparation of p-hydroxylethyl vinyl ketone synthons has been accomplished using a PhMc2Si unit as a masked hydroxyl group (eq 3).  

The method has been used to prepare intermediates for intramolecular Diels-Alder reactions (eqs 4 and 5). The title reagent may provide ether the diene for the intramolecular Diels-Alder (eq 4) or, after hydrolysis, the dienophile (eq 5).  

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Other Methyldiphenylsilylations. Methyldiphenylchlorosilane was used to form 6-silyluracils and uridines. The yields were better than those obtained with chlorotrimethylsilane (eq 9). The methyldiphenylsilylation of the lithium anion of 3-triethylsilyloxy-l,4-pentadiene occurs to place the methyldiphenylsilyl group on the 1-position, providing, after deprotection, the 8-methyldiphenylsilyl ketone (6) (eq 10). ... 

Table 1 Regioselective reactions of 3-Triethylsilyloxy-l,4-pentadiene with typical electrophiles...

General Discussion. 3-Triethylsilyloxy-l,4-pentadiene may be used to prepare the useful 3-triethylsilyloxypentadienyl anion via metalation with sec-butyUithium (eq 1). ... 

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