How to start an approach in IMC loss of communication under IFR?
The FAA says (per 14 CFR 91.185):


  If the clearance limit is not a fix from which an approach begins,
  leave the clearance limit at the expect-further-clearance time if one
  has been received, or if none has been received, upon arrival over the
  clearance limit, and proceed to a fix from which an approach begins
  and commence descent or descent and approach as close as possible to
  the estimated time of arrival as calculated from the filed or amended
  (with ATC) estimated time en route.


This seems to answer your question unless you have a more specific one. You can descend to an IAF as you see fit and commence any approach. ATC will clear the way.