A computational study on the substituent effect of diallylamine monomers in their cyclopolymerization reactions

The cyclization reactions of N-methyl-N,N-diallylamine (1), N-methyl-N-allyl-2-(methoxycarbonyl)allylamine (2), and N-methyl-N-methallyl-2-(methoxycarbonyl)allylamine (3) have been modeled in their cyclopolymerization mechanism. The experimentally observed regioselectivity has been reproduced and explained in terms of steric and electronic factors. The activation energies for the cyclization of the model compounds representing 1, 2, and 3 are 5.41, 8.68, and 11.59 kcal/mol, respectively. The ester substituent on 2 and 3 is found to increase the activation energy of the exo transition structure by its steric effect without making a significant effect in the barrier height of endo. The destabilization on the exo transition structure is enhanced by methyl substitution on the double bond. The experimentally determined stereoselectivity for 1 and 2 have also been reproduced. The lower activation energy for 1 despite its low polymerizability is justified by considering the dominance of competing reactions, like H-abstraction and homopolymerization.