1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile and Vinyl Ethers: Cyclic Ketene Imines on the Pathway to 1 : 2 Cycloadducts

Abstract

(E)‐ and (Z)‐1,2‐bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile (BTE; (=E)‐ and (Z)‐1,2‐bis(trifluoromethyl)but‐2‐enedinitrile) were reacted with an excess of methyl vinyl ether, used as solvent, and furnished 1 : 2 adducts 6 (54%) and cyclobutanes 3 as 1 : 1 adducts (41%). The four diastereoisomeric bis‐adducts 6 (different ratios from (E)‐ and (Z)‐BTE) are derivatives of 1‐azabicyclo[4.2.0]oct‐5‐ene; X‐ray analyses and 19F‐NMR spectra revealed their structures. Since the cyclobutanes 3 are resistant to vinyl ether, the pathways leading to mono‐ and bis‐adducts must compete on the level of the intermediate l,4‐zwitterions 1 and 2. The latter either cyclize to the cyclobutanes 3 or to six‐membered cyclic ketene imines 8 which accept a second molecule of vinyl ether to yield the bis‐adducts 6. The occurrence of the highly strained ketene imines 8 gains credibility by comparison to stable seven‐membered cyclic ketene imines recently reported.