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1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile and Vinyl Ethers: Cyclic Ketene Imines on the Pathway to 1 : 2 Cycloadducts
Author(s) -
Urrutia Desmaison Gonzalo,
Huisgen Rolf,
Nöth Heinrich
Publication year - 2012
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.201200047
Subject(s) - ketene , chemistry , cyclobutanes , adduct , trifluoromethyl , cycloaddition , ether , medicinal chemistry , yield (engineering) , stereochemistry , organic chemistry , catalysis , alkyl , materials science , metallurgy
( 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 19 F‐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.