Question

Show how you would use a protecting group to convert 4-bromobutan-1-ol to hept-5-yn-1-ol.

Short answer

Triisopropylsilyl chloride is used as protecting group for the protection of hydroxyl group. Base is used to abstract the proton from hydroxyl and convert it into good nucleophile so that attack of nucleophile can be easily facilitated on TIPS group.

Protection of hydroxyl group using TIPS chloride as protecting group

Step-by-step solution

Step-1. Protection of hydroxyl group in 4-bromobutan-1-ol:

Triisopropylsilyl chloride is used as protecting group for the protection of hydroxyl group. Base is used to abstract the proton from hydroxyl and convert it into good nucleophile so that attack of nucleophile can be easily facilitated on TIPS group.

Protection of hydroxyl group using TIPS chloride as protecting group

Step-2. SN2 attack and deprotection of protecting group:

Propyne on treatment with sodium amide which acts as a base abstracts acidic proton from terminal alkyne and converts it into good nucleophile which attacks at the product formed in first step, and forms another product which further on deprotection with tetra-n-butylammonium fluoride forms the required product, that is, hept-5-yn-1-ol.

Formation of the product hept-5-yn-1-ol