Summary: The [3+ 41 cycloaddition of 1, 1, 3, 3-tetramethylindane-2-thione S-methylide (1 1) and 2, 3-bis (trifluoromethy1) fumaronitrile (2c) afforded 86% of the ketene imine 14, the X- ray structure of which revealed a strained ring; the thermolysis to thione 9+ cyclopropane 18 constitutes a novel reaction course.
![trans-2,3-dihydro-1,1,3,3-tetramethyl-3',4'-bis(trifluoromethyl)-spiro[1H-indene-2,2'-thiolane]-3',4'-dicarbonitrile Structure](https://image.chemsrc.com/caspic/496/125610-31-3.png)
