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Alkynyl silanes are used for protection and activation

المؤلف:  Jonathan Clayden , Nick Greeves , Stuart Warren

المصدر:  ORGANIC CHEMISTRY

الجزء والصفحة:  ص671-672

2025-07-03

725

Terminal alkynes have an acidic proton (pKa ca. 25) that can be removed by very strong bases such as organometallic reagents (Grignards, RLi, etc.). While this is often what is intended, in other circumstances it may be an unwanted side reaction that would consume an organo metallic reagent or interfere with the chosen reaction. Exchange of the terminal proton of an alkyne for a trimethylsilyl group exploits the relative acidity of the proton and provides a neat solution to these problems. The SiMe3 group protects the terminus of the alkyne during the reaction but can then be removed with fluoride or sodium hydroxide. A classic case is the removal of a proton next door to a terminal alkyne.

Additionally, acetylene itself is a useful two-carbon building block but is not very convenient to handle as it is an explosive gas. Trimethylsilylacetylene is a distillable liquid that is a convenient substitute for acetylene in reactions involving the lithium derivative as it has only one acidic proton. The synthesis of this alkynyl ketone is an example. Deprotonation with butyl lithium provides the alkynyl lithium that reacted with the alkyl chloride in the presence of iodide as nucleophilic catalyst. Removal of the trimethylsilyl group with potassium carbonate in methanol allowed further reaction on the other end of the alkyne.