Strategy VII Use of Acetylenes Alkynes

Background Needed for this Chapter Reference to Clayden, Organic Chemistry  

Chapter 9 Using Organometallic Reagents to Make C-C Bonds. 

This strategy chapter is rather different. We shall look at one class of starting material—alkynes or acetylenes—and see what special jobs they can do in synthesis. In particular, we shall see how they can solve some problems we have already met. Acetylene itself 3 is readily available and its first important property is that protons on triple bonds are much more acidic than most CH protons. Acetylene forms a genuine anion 4 with sodium in liquid ammonia, a lithium derivative 1 with BuLi and a Grignard reagent 2 by reaction with a simple alkyl Grignard such as EtMgX. 

These derivatives react with the type of carbon electrophiles we have already met such as alkyl halides, aldehydes and ketones, and epoxides to give 5, 6 and 7 respectively. 

These products still have an acidic hydrogen on the triple bond so they can react again with base and an electrophile. Surfynol 10 is clearly an acetylene diadduct with the same ketone 11 being used twice.2 

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