Under current HDB regulations, you will need to fulfil your MOP before you are eligible to purchase a private property ie exercise the option of a private property.
However, if you have a genuine reason, you may write in to HDB to ask for a waiver of the MOP period. HDB will assess the case based on the factors that you provided.
Once the MOP is reached, you may purchase the private property FIRST and dispose off the HDB subsequently if the finances is not an issue.