Retry a jquery ajax request which has callbacks attached to its deferred

You could use jQuery.ajaxPrefilter to wrap the jqXHR in another deferred object.

I made an example on jsFiddle that shows it working, and tried to adapt some of your code to handle the 401 into this version:

$.ajaxPrefilter(function(opts, originalOpts, jqXHR) {
    // you could pass this option in on a "retry" so that it doesn't
    // get all recursive on you.
    if (opts.refreshRequest) {
        return;
    }

    // our own deferred object to handle done/fail callbacks
    var dfd = $.Deferred();

    // if the request works, return normally
    jqXHR.done(dfd.resolve);

    // if the request fails, do something else
    // yet still resolve
    jqXHR.fail(function() {
        var args = Array.prototype.slice.call(arguments);
        if (jqXHR.status === 401) {
            $.ajax({
                url: '/refresh',
                refreshRequest: true,
                error: function() {
                    // session can't be saved
                    alert('Your session has expired. Sorry.');
                    // reject with the original 401 data
                    dfd.rejectWith(jqXHR, args);
                },
                success: function() {
                    // retry with a copied originalOpts with refreshRequest.
                    var newOpts = $.extend({}, originalOpts, {
                        refreshRequest: true
                    });
                    // pass this one on to our deferred pass or fail.
                    $.ajax(newOpts).then(dfd.resolve, dfd.reject);
                }
            });

        } else {
            dfd.rejectWith(jqXHR, args);
        }
    });

    // NOW override the jqXHR's promise functions with our deferred
    return dfd.promise(jqXHR);
});

This works because deferred.promise(object) will actually overwrite all of the “promise methods” on the jqXHR.

NOTE: To anyone else finding this, if you are attaching callbacks with success: and error: in the ajax options, this snippet will not work the way you expect. It assumes that the only callbacks are the ones attached using the .done(callback) and .fail(callback) methods of the jqXHR.