I solved the Access-Control-Allow-Origin error modifying the dataType parameter to dataType:’jsonp’ and adding a crossDomain:true
$.ajax({
url: 'https://www.googleapis.com/moderator/v1/series?key='+key,
data: myData,
type: 'GET',
crossDomain: true,
dataType: 'jsonp',
success: function() { alert("Success"); },
error: function() { alert('Failed!'); },
beforeSend: setHeader
});