1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile: Enol Ethers and Ketene Acetals as Cycloaddition Partners

Abstract

(E)‐ and (Z)‐1,2‐bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile ((E)‐ and (Z)‐BTE, resp., =(E)‐ and (Z)‐2,3‐bis(trifluoromethyl)but‐2‐enedinitrile) were used as a stereochemical probe in studying (2+2) cycloadditions of acceptor with donor alkenes. The additions to methyl (E)‐ and (Z)‐propenyl ether gave rise to the eight conceivable cyclobutanes 8, although in different ratios in reactions of (E)‐ and (Z)‐BTE. The 19F‐NMR data served the structural assignment and the quantitative analysis. The mechanistic discussion is based on rotations and ring closures of the assumed 1,4‐zwitterionic intermediates. Dimethylketene dimethyl acetal, methylketene dimethyl acetal, and ketene diethyl acetal show an increasing rate in their reactions with BTE as well as in the equilibration of the cycloadducts.

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

“…Unexpectedly, the electron‐deficient dimethyl dicyanofumarate, known as a reactive Michael acceptor24a and dienophile,24b did not undergo the reaction with 28 even after seven days at room temperature. Extremely reactive fluorinated alkenes such as trans ‐1,2‐bis(trifluoromethyl)‐1,2‐dicyanoethylene24c and 1,1‐bis(trifluoromethyl)‐2,2‐dicyanoethylene24d were also unreactive towards 1,3‐diene 28 . Very likely, steric hindrance caused by the bulky adamantane moiety is the reason for the observed inertness of 28 .…”