Facile and Convenient Synthetic Methods for Bis(trifluoroacetyl)ketene N,O-, N,S- and S,S-Acetals and 2,2-Bis(trifluoroacetyl)vinylamines and Sulfides - Hojo, Masaru; Masuda, Ryoichi; Okada, Etsuji; Mochizuki, Yasuyuki (Synthesis, 1992)