If Windows 8.1 or 2018 R2 Preview setup fails when you try installing on Oracle VirtualBox, try the following:
"c:\Program Files\Oracle\VirtualBox\VBoxManage.exe" setextradata "vbox_W2012R2_Prev" VBoxInternal/CPUM/CMPXCHG16B 1
9431.0.WINMAIN_BLUEMP.130615-1214_X64FRE_SERVER_SOLUTION_EN-US- IMP_SSSO_X64FRE_EN-US_DV5.ISO
and run and install Windows. With serial numbers, using these serial numbers (not sure if you got same serial numbers):
Windows Server 2012 R2 Essentials Preview now supports two types of activation:
Product Key :
N4F2V-VRDD2-7VQ6J-JJYHK-WTT88
for Automatic Virtual Machine Activation (AVMA), the key was:
7VW9N-8C48X-J6442-J3KM6-FVTM9