Ene reaction transition state

As the argument has been presented above, this rationalization does not appear to be impossible. However, Figure 3 shows a tabulation of all of the model compounds synthesized to date in an attempt to model the behavior of AH. Although the second and third compounds in the list are reported to initiate polymerization, MCH does not. Furthermore, as shown in Figure 3, a compound that would appear to give an even more hindered ene reaction transition state than AH also does not initiate the polymerization of styrene (private communication from D. Aue). This is hard to reconcile with a rationalization of the lack of MAH reaction by methylene-cyclohexadiene based on the hindrance of its ene reaction. 

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