Starting in 2013.1, XST is not part of the Synthesis Settings Strategy Options by default. How can XST be added and run within the Vivado tools environment?
To make XST available as part of the Synthesis Settings Strategy Options, the following Tcl command needs to be specified using the Vivado tool Tcl console:
set_param project.enableXSTFlows 1
The above Tcl command adds XST as part of the Synthesis Setting Strategy Options within the Vivado tool, then you can use XST for running designs.