Making a very sharp turn by pivoting on your front wheel?
In german this is called "Hinterrad versetzen" -- "displacing the back wheel". I got to learn this in an mtb course I took a while back. If you can, try to find an instructor or other experienced rider to teach you.

How to practice:

Start very, very small and always wear full protective gear, i.e. a full-face helmet and vest in case you crash. You will crash. Be prepared. Have a friend with you just in case.

Look for an open, empty and even space like a parking lot or similar where you can brake without fear of slipping. If possible, avoid concrete or similar very hard surfaces.

First, you practice the stoppie, without turning. Start small, i.e. just lift your back wheel a couple of centimetres. You don't need to ride very fast, it's mostly about the balance on the bike. It's absolutely possible to do this from a walking pace. Instead of moving your weight far back, as you normally would in a hard stop, keep it (more or less) in front. Find the point where it's easy to lift the back wheel without getting the feeling you will crash any moment. Do this a couple of times. Slowly increase the height of the back wheel. 

Do only the stoppie until you feel comfortable "standing on your front wheel" for a second or two without losing control.

If you feel safe holding the stoppie, try pushing your back wheel around a couple of centimetres by letting the inertia turn the bike. You need only provide the tiniest motion yourself, physics will do the rest. Slowly increase the arc until you are where you want to be.

Note 1. If you have front suspension, beware of your fork kicking back when in the stoppie. This can easily overturn you.

Note 2. I wouldn't try this on stairs or a rocky or otherwise dangerous path until I was absolutely sure I can do it. Also, don't force it. Practicing this kind of thing takes time and drains you faster than you think. Try integrating training into normal rides instead of riding out just to train.