Move Calendar event to Reminders?
This seems to work:


Open your calendar.
Click on the event you want to move to Reminders.
Copy the event (&#8984; command+C).
In the Reminders app, click in a new event line.
Paste the event (&#8984; command+V).


There are a couple things I noticed when testing this (on Mac OS Sierra, 10.12.6):


The title of the reminder matches the name of the calendar event, but it's followed by "Scheduled:".
If the calendar event contains any alerts prior to the time of the event, these alerts are not added to the reminder.  The reminder is only for the actual time of the event.