Cycloaddition of cyclopropanone acetals to tetracyanoethylene

Article abstract of DOI:10.1021/jo00321a028

The cyclopropanone acetals 1a-e and tetracyanoethylene give in a thermal [σ2 + π2] cycloaddition 2,2,3,3-tetracyanocyclopentanone acetals 2a-e. In the case of 2-methylcyclopropanone acetal 1c the corresponding 5-methylcyclopentanone acetal 3c is also formed in minor amounts. With respect to the parent compound methyl substituents in the cyclopropane ring (1b-c,e) retard the cycloaddition reaction, whereas a phenyl group (1d) accelerates the reaction. The cycloadducts 2 are converted by water mainly into the ring-opened esters 4. The structures of compound 2 have been determined by ¹H and ¹³C NMR.