Protection of Triple Bonds

Masking the potentially acidic proton of 1-alkynes (p. 25) is readily achieved by their conversion to the corresponding l-silyl-l-alkynes. ° 

Depending on the nature of the trialkylsilyl group, it can be removed under a variety of conditions (MeONa in MeOH, n-Bu4NF in THF, or AgNOj in EtOH followed by NaCN ° ). 

Protection of an internal triple bond (or an internal triple bond in the presence of a double bond) can be done by converting the former to the dicobaltoctacarbonyl complex. The following alkene hydroboration-oxidation example illustrates this approach.  

Reagents. Give the structures of the major products (A-G) expected from the following reactions. Assume standard aqueous workup conditions are used for product isolation. 

Selectivity. Show the product(s) expected for the following transformations, o OMe 

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