Theoretical Studies Of The Reaction Mechanisms Of 6-Benzyl-6-azabicyclo[2.2.1]hept-2-ene And Benzoyl Isocyanate And The Rearrangement Mechanisms Of (2E, 4E)-5-(diallylamino)-2-methypenta-2.4-dienal

In this paper, mechanisms of two organic reactions have been studied by using density functional theory (DFT). The first one is the mechanism on 6-benzyl-6-aza-bicyclo[2.2.1]hept-2-ene with benzoyl isocyanate at the room temperature to give urea and isourea. And the second one is about the rearrangement mechanism of (2E,4E)-5-(diallylamino)-2-methypenta-2.4-dienal at high temperature.Reaction mechanisms of the 6-benzyl-6-aza-bicyclo[2.2.1]hept-2-ene with benzoyl isocyanate have been investigated at the B3LYP/6-31G(d,p) level of theory. The reaction proceeding along six competitive channels includes two categories. That is, two channels are formally [3,3]-sigmatropic rearrangements and four channels are [4+2] cycloadditions. For urea, the formally [3,3]-sigmatropic rearrangement channel and the [4+2] cycloaddition channels are competitive since they have similar barriers. However, the [4+2] cycloaddition channels are energetically favorable pathways to lead to isourea, with the highest barrier of 12.77 kcal/mol. These polar Diels-Alder (P-DA) reactions are controlled by the charge transfer (CT) at the transition states. Moreover, the main products of this reaction include urea and isourea. Furthermore, difference of two new bond lengths at transition states indicate that the [4+2] cycloadditions in this reaction are asynchronous processes, which is good consistent with the experiment.The rearrangement mechanisms of the (2E, 4E)-5-(diallylamino)-2-methypenta-2.4-dienal at high temperature have been investigated at the B3LYP/6-31G (d,p) level of theory as well. The reaction is initiated by migration of the hydrogen atom which probably proceeds along three competitive channels, including the two categories intermolecular migrations and one intramolecular migration. The calculated results demonstrates that path C (intermolecular migration) is the energetically favorable pathways to the important zwitterionic intermediate, with the lowest energy barrier 44.69 kcal/mol. Furthermore, the first hydrogen atom migration is also the rapid decision in the overall reaction. And the configuration changes from E to Z during the hydrogen migration. 1,5-diallyl-3-methyl-5,6-dihydropyridin-2(1H)-one (PI) is obtained by [3, 3]-sigmatropic rearrangement from zwitterionic intermediate. And (3aR,7aS)-2-allyl-7a-methyl-3,3a,4,5-tetrahydro-2H-isoindol-1(7aH)-one (P2) is given through [4+2] cycloaddition. The energy of P2 is 18.01 kcal/mol lower than that of P1, demonstrating that P2 is more energy favorable than P1, which is consistent well with the experiment.