Rotate Around by 90 Degrees

Is there a way to use the RotateAround function by a certain amount of degrees

For example, I have:

transform.RotateAround(v3Pos,  transform.right, Time.deltaTime * speed);

How would you modify this code to rotate by 90 degrees in the right direction and then stop?

Before rotation begins, get the euler angle around which you are rotating (looks like X), then in update check to see if current angle is >= that angle+90 (mod 360 of course)