Computational study of singlet and triplet sulfonylnitrenes insertion into 1,3-butadienes: 1,2- or 1,4-cycloaddition?

摘要

The formation of N-trifluoromethylsulfonyl-2-vinylaziridine and N-trifluoromethylsulfonyl-3-pyrroline by the reaction of the singlet and triplet trifluoromethanesulfonylnitrenes with s-cis- and s-trans-1,3-butadienes was studied theoretically at the B3LYP/6-311++G(d,p) and M06-2X/6-311++G(d,p) levels of theory. The singlet trifluoromethanesulfonylnitrene adds to s-cisand s-trans-1,3-butadiene exothermally in one step to give the product of 1,2-cycloaddition, N-trifluoromethylsulfonyl-2- vinylaziridine, the energy decreasing by 88.5 and 86.2 kcal/mol at the B3LYP level and by 105.2 and 103.0 kcal/mol at the M06-2X level, respectively. The formed 2-vinylaziridine can undergo rotation about the C(2)-C_(sp2) bond with the barrier not exceeding 3.5 kcal/mol and to rearrange into N-trifluoromethylsulfonyl-3-pyrroline. The triplet trifluoromethanesulfonylnitrene reacts with s-cis- and s-trans-1,3-butadiene in two steps. The first exothermic step is the formation of the triplet diradical adducts. The second step is the spin inversion with the energy raising by 5.8 and 17.8 kcal/mol at the B3LYP level and by 11.0 and 20.8 kcal/mol at the M06-2X level for the adducts to s-cis- and s-trans-1,3-butadiene, respectively. Recombination of the radical centers occurs selectively to give N-trifluoromethylsulfonyl-2-vinylaziridine that is exothermally rearranged into N-trifluoromethylsulfonyl-3-pyrroline with the energy barrier of 40 kcal/mol at the B3LYP level and of 50 kcal/mol at the M06-2X level.