All of the types you mentioned are library constructs, not syntax.
Macros are syntax though.
Macros are syntax though.
In terms of syntax, you create a box with Box::new just like you might any other struct.
EDIT: anyway I'm not saying that means that your underlying issue isn't real, just that I think describing it as "syntax" makes the issue confusing to understand. It sounds to me like maybe you think Rust programs are too verbose?