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

(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.