G280 Captain reported encountering wake turbulence on approach to IAD in trail of a B787.

Narrative

While on the GIBBZ4 arrival to IAD; we were at 6000 nearing GIBBZ. I noticed on TCAS and aircraft about 5 miles ahead descending. As the aircraft ahead made the turn at GIBBZ; I saw that it was a very large airplane. I requested a vector from the Approach Controller for wake turbulence. The Controller responded; 'No; he's 5.5 miles ahead; slow to 210 knots'. We continued the arrival as cleared and while making the south turn at GIBBZ; for a north landing; I noticed the wind was relatively very light; 10 knots from 360 degrees. I became concerned that the preceding aircraft's wake would likely be very close to course. Shortly after making the south turn; we encountered wake turbulence; still at 6;000 feet. The aircraft rolled and yawed abruptly to left; exceeding 30 degrees bank. We again requested a vector. The Controller cleared us to descend to 5;000 feet. Reaching 5;000 feet we encountered the wake turbulence again. This time the aircraft rolled violently to the right; the airframe shuddered and the nose dropped consistent with an aerodynamic stall. After losing about 300 feet; the aircraft was manually returned to level flight at assigned altitude. We again requested vectors for additional spacing. The Approach Controller then extended our downwind while turning the preceding aircraft onto the base leg. The final Controller vectored us to final and gave multiple warnings of wake turbulence; being in trail of a [B787]. We flew the entire approach to landing above glide path for wake avoidance and did not have any further encounters.