Synchronize to another remote directory

Hello,
is it possible to do synchronize local-folder1 remote-folder2 -preview and copy the files not in local-folder1 into the remote-folder3?

You can use WinSCP .NET assembly and its Session.CompareDirectories method to find the differences.
https://winscp.net/eng/docs/library_session_comparedirectories

Then you can iterate the differences and apply them to the third folder.