Cause and result?

Thermodynamically, I would say, no, it's not possible. Every step will lose energy, you've defined a closed system, so the last step can't cause the first, there would have to be an energy input in one of the steps. There's nothing to replenish the potential energy of the system.

On a non-scientific note, maybe if you had some kind of theoretical situation in which there was a group of people reacting in series, a hits b, b hits c, c hits d, etc. Each hit makes a person mad, so that person hits someone, that might work. It's a highly stylized thought experiment. And along with being hit, each person would have to have the condition that being hit by one person would make them hit another. So, there would have to be conditions it would work. It would only work if there was another cause, another thing giving input, so I think the answer to this situation would also be no. Because it's a closed system.

Unless you meant would it work if it was not a closed system, in which case, yes, to both.

It would seem to me if the entirity is the question, it would depend on where you started in the cycle. If you started (your alphabet does not have an absolute zero as a time line or measurment would) with the letter "D" and went through the entire alphabet (making D the point of entry) would cycle around causing D to be responsible for anything happening after that.

If "D" represented an action in a city on a map... and I started at D and cycled around in a circle to all of the actions in all of the cities in sequence came back to "A" ... to complete the cycle all the way to A again... then D could be the cause of "A"

It would depend entirely on how your alphabet position is guaged.

No, A is the cause of D.