Getting the -exec option in find to work

Okay, I am trying to make 'find' print out a list of directories that contain files other than jpgs, but I think my use of the -exec option is broken. My environment is Cygwin Bash.

$ find ! -iname "*.JPG$" -exec dirname

find: missing argument to `-exec'

$ find ! -iname "*.JPG$" -exec dirname {}

find: missing argument to `-exec'

$ find ! -iname "*.JPG$" -exec dirname;

find: missing argument to `-exec'

$ find ! -iname "*.JPG$" -exec dirname ;

find: missing argument to `-exec'

$ find ! -iname "*.JPG$" -exec dirname {};

find: missing argument to `-exec'