The use of 2 - chloroacrylonitrile as dienophile is a viable synthetic equivalent for ketene 3 - dienes .
Ketene is a structure that typically underdoes a ( 2 + 2 ) cycloaddition to give a cyclobutanone dimer rather than participating in Diels -- Alder reactions with 1 .
The use of 2 - chloroacrylonitrile as dienophile is a viable synthetic equivalent for ketene , a structure that typically underdoes a ( 2 + 2 ) cycloaddition to give a cyclobutanone dimer rather than participating in Diels -- Alder reactions with 1 , 3 - dienes .