I am having trouble with coming up with an advanced search syntax to find folders that does not contain a specific folder name "Legal" Any suggestions? thanks.
There is no search syntax to perform this search. See this thread for an alternative solution.
The syntax {LF:ChildName="Legal", Type=F} will return all folders that do contain a folder named Legal (as a direct child, not a subsubfolder), so you can use the NOT operator to combine this with a search that returns all the potential folders, such as looking for a specific template or within a section of the repository:
Examples:
Searching for folders that have the template "Clients" but do not contain a folder called "Legal":
{[Clients]}-{LF:ChildName="Legal", Type=F}
Looking in the folder "All Clients" for folders that do not contain a folder called "Legal"
{LF:LOOKIN="RepoName\All Clients"}-{LF:ChildName="Legal", Type=F}