How to buy a lease land from landlord

Hi, If Mr.A is willing to purchase a vacant land from the landlord which is leased to some one for 30 years and the lease expires on Jan/2034. 

The land lord says that he will give a Irrevocable power to A name and signs the sale deed with the value of land and it can be registered only after the expiry of lease.

OR

Kindly suggest whether Mr. A can buy and register the land on his name before the expiry of lease. 

Pl Note: There is no condition stated in the lease agreement about the sale of land.

Kindly suggest what is the solution to go with Landlord or A or there is any other way

Thank you.