Well, "syntactic sugar" usually refers to things that can be translated in a syntactically local, structure-preserving way. I'm aware that generators can be compiled down to an ES5 representation, but it requires non-trivial analysis. Take a look at the example on their home page: https://facebook.github.io/regenerator/.

Do you also consider functions to be syntactic sugar? Because you can also implement them in terms of a switch statement.