Ethylene, 1,1-dicyano cycloaddition reactions

A synthetically useful pressure-induced increase of diastereoselectivity was also found for normal Diels-Alder reactions such as the cycloaddition of the phenyl butadienes (93a-c) with the dicyano ethylenes (94-97) to yield the ds-adducts 98a-d, lOOa-d and 102a-d as well as the trous-adducts 99a-d, lOla-d and 103a-d (Scheme 8.24) [54]. 

The title reaction exemplifies intriguing features of transition metal catalysis. In the absence of transition metal catalysts, reaction between bicyclo[2.1.0]pentane (11) and electron-poor olefins requires extremely forcing conditions and produces a very complex mixture. For example, because of the molecular orbital (MO) restrictions, tmns-l,2-dicyano-ethylene enters into the 2 + 2 cycloaddition across the central o- bond. 

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