The reaction mechanisms as well as substituted effect and solvent effect of the enyne-allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers-Saito and Schmittel reactions. The Myers-Saito reaction of non-substituted enyne-allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C 2 -C 7 cyclization and more exothermic (δ R E = -69.38 kcal/mol). For R1=CH 3 and t-Bu, the increasing barrier of the C 2 -C 7 cyclization is higher than that for the C 2 -C 6 cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron-releasing group. Moreover, the strong steric effect of R 1 = t-Bu would shift the C 2 -C 7 cyclization to the [4 + 2] cycloaddition. On the other hand, for R 1 =Ph, NH 2 , O - , NO 2 , and CN substituents, the barrier of the C 2 -C 6 cyclization would be more diminished than the C 2 -C 7 cyclization due to strong mesomeric effect; the reaction path of C 2 -C 7 cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential-energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water.
- Diels-Alder reaction
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry