Catalyzes the conversion of dTDP-alpha-D-fucopyranose to dTDP-alpha-D-fucofuranose. This is a step in the biosynthesis of D-fucofuranose, a component of E.coli O52 O antigen. dTDP-alpha-D-fucose = dTDP-alpha-D-fucofuranose Binds 1 FAD per subunit. Inhibited by Cu(2+), while other divalent cations such as Ca(2+), Co(2+), Fe(2+) and Mg(2+) have no obvious effects on enzyme activity. kcat is 3.3 min(-1). Optimum temperature is 15-37 degrees Celsius. Bacterial outer membrane biogenesis; LPS O-antigen biosynthesis. Cells lacking this gene produce semirough (SR-type) LPS with only one O unit attached to the core-lipid A moiety while the wild-type strain produces normal LPS. Belongs to the UDP-galactopyranose/dTDP-fucopyranose mutase family.