trifluorormethanesulfonic acid in tetrahydrofuran
-127 deg C. 1 h, then room t., 16 h; Yield given. Yields of byproduct given. Title compound not separated from byproducts;
Bergmann et al.
Recueil des Travaux Chimiques des Pays-Bas, 1952 , vol. 71, p. 168,192
Journal of the American Chemical Society, 1953 , vol. 75, p. 358