Not sure whether it is illegal. I certainly don't like the imperialistic US view that their sanctions are globally binding. Citizens and businesses from other countries should not be bound by US laws while not being on US ground.

But I think that these sanctions against Russia are ethically justified. So circumventing them is unethical for me, whether illegal or not.

Edit: Saying that these sanctions are ethically justified does not imply that they would be the most efficient or effective way to stop the war.