Using shell expansion with Ansible -

i'm trying execute remote command via ansible requires gathering pid of process:

ansible webserver -m shell -a 'jstack -l $(pgrep -f java)' 

however seems ansible not able expand shell command contained in parenthesis (tried grave accent):

127.0.0.1 | failed | rc=1 >> usage:     jstack [-l] <pid> 

executing command in expansion reveals expansion not take place:

ansible webserver  -a 'echo $(pgrep -f java)' 192.168.0.1 | success | rc=0 >> $(pgrep -f java)