I don't know of any ejection seats that go sideways, but early F-104 models had a downward track ejection seat. The main issue is that parachutes need some time to open and helicopters tend to fly pretty low. So in most situations you wouldn't be in a safe altitude to actually eject.
Modern zero-zero seats can safely eject at any altitude, but they do so by using a rocket motor to fly upwards to a safe altitude for the parachute to open. So because of the rotors, helicopters generally don't have ejection seats. The exception is the Kamov KA-50 series. It has explosive bolts blowing off the rotors before ejection.
Presumably less "blowing off" and more "letting go." They're already being spun with as much centripetal force as they'll tolerate. The explosive only needs enough oomph to make itself disappear.
Which had to be a weird pitch. Like, 'for safety reasons, we're going to stitch this together with detcord.'