Mortgage interest deduction when paying cash for initial purchase

[Jean-Thierry Aleman]

I am about to acquire a property using cash so we can do a fast close. I am then going to finance it with standard mortgage.  I thought I could deduct the mortgage interest from the loan but read somewhere I can't do that if I purchase it with cash initially. Is this true? And if so, any thought on how to overcome this obstacle and deduct the interest?

Thanks