8π-Six-atom rings: 1,3,4,5-oxa- and -thia-triazines and 1,2,3,5-tetrazines from an extended tandem reaction: reactions of 1,2,3-triazolium-1-imides with (E)-cinnamaldehyde, methyl cyanodithioformate, and aryl-N-sulphinylamines: new tetrahydro-oxazolo[4,5-d]-1,2,3-triazoliumides and triazaspiro-[4.4]