2,4-Bis(bromomethyl)-3-methylthiophene was synthesised as an intermediate to prepare the strained thiophenobenzophanediene 11, which readily thermally valence isomerizes to the novel thia[13]annulene 10. This thia-annulene is notably diatropic and shows about 40% of the ring current of the parent bridged [14]annulene 9, which is substantially more than an analogous oxaannulene, 18, and substantially less than the azaannulene 19.