B757 Flight crew reported multiple EICAS issues upon reaching cruise altitude. Diverted and landed uneventfully.

Narrative

Our day started with a XA:00 short call reserve assignment. We were assigned to a XD:00 report for a ZZZ ZZZ confirmation flight and then a ferry flight ZZZ ZZZ1. During the ferry flight; ZZZ ZZZ1; approximately one minute after reaching cruising altitude at FL400; We received a master caution and multiple EICAS issues. The root issue was R AC BUS OFF. Associated messages included R PACK OFF; AND L ENG EEC (Electronic Engine Control). The R GEN CONT off button light was illuminated on the overhead electrical panel; along with the BUS TIE ISLN button light.The autopilot disengaged. The auto throttle disengaged. The flight director pitch command bar was gone; several aircraft lights extinguished; and ATC reported that they were not receiving our transponder.With the first officer flying; I first ran the R AC BUS OFF non normal checklist. Per the checklist; the R ENG GEN CONT reset; restored power to the right AC BUS; however the BUS TIE ISLN light meant that the right AC BUS WAS ISOLATED with no backup power. We checked the BUS ISOLATED checklist; and it stated that the button could not be reset unless directed by the AC BUS OFF CHECKLIST. We double checked the AC BUS OFF checklist and we were not directed to reset the BUS TIE BUTTON.We ran the R PACK OFF checklist; however there were no actions to take regarding the pack.The L ENG EEC checklist directed us to reduce thrust to thrust lever mid position and turn off both EECs. We requested a descent to FL300 and received; initially FL 350. During the descent; we ran the checklist. When complete; we reset both flight directors and the pitch commands were restored. We verified the MCP (Mode Control Panel); and re-engaged the autopilot and auto throttle. The checklist stated that the auto throttle provides maximum thrust limiting and that normal thrust management could be resumed with the observation of thrust limits.We coordinated with Dispatch and with Maintenance Control. Due to the fact the the R AC BUS was isolated with no back-up protection; when considering the time of night; the possibility of fatigue later in flight; the startle factor associated with the R AC BUS unpowered; and the increased workload that could be created during a critical phase of flight we elected to divert to ZZZ2. We [requested priority handling] with ATC and landed without further incident.