It turned out the error message was missleading. There was no problem with whitespaces in path but with a permission on a subfolder.
Thanks a lot for everyone helping me with this problem. To sum up: You don't need to escape whitespaces in a path at all when using a shell to execute commands. Whitespaces causing no problem at all.
If you want to escape whitespaces on OS X you may:
a) use quotes, i.e. "/Users/user1/Library/Application Support/b4j.example" (in B4x """")
b) user single quotes, i.e. 'Users/user1/Library/Application Support/b4j.example'
c) escape whitespaces, i.e. Users/user1/Library/Application\ Support/b4j.example
Thanks a lot to everyone, helping
Thomas