Question

Consider the above synthesis. What is wrong with this transformation?

• A. $B{H}_3$ is actually unreactive towards alkyne.
• B. $B{H}_3$ should add to adjacent carbon rather than the same carbon.
• C. Boron can be used as an electrophile only with non-terminal alkyne.
• D. The borane addition follows regiochemistry opposite to that shown.

Answer 1

Answer: (D)

The borane addition follows regiochemistry opposite to that shown.

In the given synthesis, the borane addition follows regiochemistry opposite to that shown. In the product -OH group should be added to terminal C atom which will given an aldehdye and not a ketone. This reaction follows anti-markovnikov's rule. The corrected reaction sequence is as shown.