The actual command would be:
git rebase --onto newbranch1 branch1 branch2
That will replay on top of new_branch1 all commits after branch1 up to branch2 HEAD.
As Joshua Goldberg puts it in the comments:
git rebase --onto <place-to-put-it> <last-change-that-should-NOT-move> <change to move>
As Denis Sivtsov illustrates in the comments:
If you need only replay the last commit only from branch, in this case work:
git rebase --onto newbranch1 HEAD~1