Something like this?
var fName = app.activeDocument.name;
fName.match(/(.*)(\.[^\.]+)/) ? fName = fName.match(/(.*)(\.[^\.]+)/):fName = [fName, fName];
fName[1]+'.psd';
var myFile = new File('~/Desktop/'+fName[1]+'.psd');
var saveFile = myFile.saveDlg(undefined,"Photoshop:*.psd");
if(saveFile) { app.activeDocument.saveAs( saveFile, new PhotoshopSaveOptions() ); }
Have fun